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Since 2021, as part of the research for What We Owe the Future, I have been working on a report on climate change from a longtermist perspective. The report aims to provide the most complete treatment of that question yet produced. The executive summary is below and the full report is here, available at the What We Owe the Future supplementary materials webpage.  I am grateful to the expert reviewers of the report for their comments. Views and mistakes are my own. 


Executive Summary

In this report, I will evaluate the scale of climate change from a longtermist point of view. Longtermism is the idea that influencing the long-term future, thousands of years into the future and beyond, is a key moral priority of our time. 

In economics, longtermism is embodied by the idea that we should have a zero rate of ‘pure time preference’: we should not discount the welfare of future people merely because it is in the future. Economists who embrace a zero rate of pure time preference will tend to favour more aggressive climate policy than those who discount future benefits. 

Climate change is a proof of concept of longtermism. Every time we drive, fly, or flick a light switch, each of us causes CO2 to be released into the atmosphere. This changes the amount of CO2 that is in the atmosphere for a very long time: unless we suck the CO2 out of the atmosphere ourselves, concentrations only fall back to natural levels after hundreds of thousands of years. The chart below shows long-term CO2 concentrations after different amounts of cumulative carbon emissions. 

Source: N. S. Lord et al., ‘An Impulse Response Function for the “Long Tail” of Excess Atmospheric CO2 in an Earth System Model’, Global Biogeochemical Cycles 30, no. 1 (2016): 2–17, https://doi.org/10.1002/2014GB005074.

Some of the ecological effects of climate change get worse over time. The clearest example of this is sea level rise. On current policy, the most likely sea level rise this century is 75cm. However, over 10,000 years, sea levels will rise by 10 metres. Over the long-term, the world will look very different.

From a longtermist point of view, it is especially important to avoid outcomes that could have persistent and significant effects. These include events like human extinction, societal collapse, a permanent negative change in human values, or prolonged economic stagnation. If we go extinct, then that would be the end of the human story, and there would be no future generations at all. If civilisation collapses permanently, then future generations will be left much worse off than they could have been, living lives full of suffering rather than ones of flourishing.

The anatomy of climate risk

The overall size of climate risk depends on the following factors:

  1. Greenhouse gas emissions
  2. The climate change we get from different levels of emissions
  3. The impacts of different levels of climate change

There is uncertainty about all three factors. The main findings of this report are as follows.

Emissions are likely to be lower than once thought

Due to recent progress on clean technology and climate policy, we look likely to avoid the worst-case emissions scenario, known in the literature as ‘RCP8.5’. The most likely scenario on current policy is now the medium-low emissions pathway known as ‘RCP4.5’. Moreover, climate policy is likely to strengthen in the future. For instance, as I was writing this report, the US Senate passed the Inflation Reduction Act, the most significant piece of climate legislation in American history.

Source: Hausfather and Peters, ‘Emissions – the ‘business as usual’ story is misleading’, Nature, 2020.   

Climate change is a great illustration of how society can make progress on a problem if enough people are motivated to solve it. This does not mean that climate change is solved, but there is significant momentum, and we are at least now moving in the right direction. 

The amount of carbon we could burn in a worst-case scenario is also much lower than once thought. Some of the literature assumes that there are 5 or even 10 trillion tonnes of carbon remaining in fossil fuels, mostly in the form of coal. However, these estimates fail to recognise that not all fossil fuels resources are recoverable. Estimates of recoverable fossil fuels range from 1 to 3 trillion tonnes of carbon. 

It is difficult to come up with plausible scenarios on which we burn all of the recoverable fossil fuels. Doing so would require (1) significant improvements in advanced coal extraction technology which is not part of the energy conversation today, but (2) a dramatic slowdown in progress in low carbon technologies that are already getting substantial policy support. 

Warming is likely to be lower than once thought 

Warming will likely be lower than once feared, in part because of lower emissions and in part because the scientific community has reduced uncertainty about climate sensitivity. Where once current policy seemed likely to imply 4ºC of warming above pre-industrial levels, now the most likely level of warming is around 2.7ºC, and the chance of 4ºC is around 5%. Moreover, where once there seemed to be a >10% chance of 6ºC on current policy, the risk now seems to be well below 1%. 

On a worst-case scenario in which we burn all of the fossil fuels, the most likely level of warming is 7ºC, and there is a 1 in 6 chance of more than 9.5ºC. 

Climate change will disproportionately harm the worst-off

The climate impacts literature suggests that climate change will impose disproportionate costs on countries at low latitude, which are disproportionately low- and middle-income and have done the least to contribute to climate change. People in Asia will have to deal with increasing flooding due to rising sea levels. Climate change will damage agricultural output, and cause droughts in countries reliant on rainfed agriculture. People in the tropics will face rising levels of heat stress. Fossil fuels also kill millions of people from air pollution in both poor and rich countries. 

Many low- and middle-income countries have essentially never experienced sustained improvements in living standards, and a significant fraction may be left worse-off than today due to climate change. This undermines one common argument for discounting the future costs of climate change - that future generations will be richer and so better able to adapt to the effects of climate change. 

We have a clear moral responsibility not to impose this harm, to reduce emissions, and to encourage economic development in poorer countries.

Average living standards will probably continue to rise

Climate-economy models confirm that the costs of climate change will fall disproportionately on poorer people, but almost all models also suggest that global average living standards in the future will be higher than today, on plausible levels of warming. Income per person looks set to increase by several hundred percent by the end of the century, notwithstanding the effects of climate change. 

‘Bottom-up’ climate-economy models included in the IPCC’s Sixth Assessment Report that add up the effects of climate impacts in different sectors and plug them into modern economic models suggest that warming of 4ºC would do damage equivalent to reducing global GDP by around 5%. One recent model, Takakura et al (2019), includes the following impacts:

  • Fluvial flooding
  • Coastal inundation
  • Agriculture
  • Undernourishment
  • Heat-related excess mortality
  • Cooling/heating demand
  • Occupational-health costs
  • Hydroelectric generation capacity
  • Thermal power generation capacity

For instance, in agriculture, the message from the climate impacts literature is that although climate change will damage food production, average food consumption per person will be higher than today, even for 4ºC of warming, due to progress in agricultural productivity and technology. This is illustrated on the chart below from van Dijk et al (2021), which shows per capita food consumption on different socioeconomic pathways.

Source: Michiel van Dijk et al., ‘A Meta-Analysis of Projected Global Food Demand and Population at Risk of Hunger for the Period 2010–2050’, Nature Food 2, no. 7 (July 2021): 494–501, https://doi.org/10.1038/s43016-021-00322-9

I have previously been critical of climate-economy models, but now believe they are more reliable than they once were. Until recently, a key determinant of aggregate impact assessments was how to model the effects of >4.4ºC because the chance of that level of warming was so high. Estimates that models arrived at were unmotivated and arbitrary in part because the literature on the impacts of >4.4ºC was sparse. However, warming of >4.4ºC now seems increasingly unlikely (<1% given likely trends in policy), and there is a rich and voluminous literature on the impact of warming up to 4.4.ºC. This makes recent bottom-up models more reliable.

However, even the best bottom-up climate-economy models underestimate the costs of climate change because they do not account for some important direct costs:

  • They do not include tipping points
  • They do not explicitly model the potential effects of climate change on economic growth and technological progress

It is unclear how much these factors would increase the overall direct costs of climate change; that is an important area of future research for climate economics. However, for levels of warming that now seem plausible, these effects seem unlikely to be large enough to outweigh countervailing improvements in average living standards. 

Bottom-up climate-economy models also do not account for indirect effects, such as conflict, which I discuss below. 

‘Top-down’ climate-economy models try to directly measure the effects of climate change on aggregate economic output, and some of these find much higher impacts from climate change, on the order of a 25% reduction in GDP for 4ºC warming. However, these results are highly model-dependent, rely on questionable econometric assumptions, and exclude several important climate impacts. In my view, the best bottom-up studies are a more reliable guide, notwithstanding their flaws. 

Although average living standards are likely to continue to rise, we also need to consider the possibility of societal collapse for other reasons, such as a pandemic or nuclear war. If there were to be a major global catastrophe, then future living standards may not actually be higher than today. Future generations trying to rebuild society would have to do so in a less hospitable climate.

Some tipping points could have very bad effects

In my view, the most concerning tipping points highlighted in the literature are rapid cloud feedbacks, collapse of the Atlantic Meridional Overturning Circulation and collapse of the West Antarctic Ice Sheet. 

Some models suggest that if CO2 concentrations pass 1,200ppm (compared to 415ppm today), cloud feedbacks could cause 8ºC of additional warming over the course of years to decades, on top of the 5ºC we would already have experienced. The impacts of this sort of extreme warming have not been studied, but it seems plausible that hundreds of millions of people would die. Moreover, people would be stuck with an extreme greenhouse world for millennia. This would extend the ‘time of perils’: the period in which we have the technology to destroy ourselves, but lack the political institutions necessary to manage that technology. It would also make it much harder to recover from a civilisational collapse caused by something else (such as a pandemic or nuclear war). However, given progress on emissions, it is now difficult to come up with plausible scenarios on which CO2 concentrations rise to 1,200ppm. 

Collapse of the Atlantic Meridional Overturning Circulation would cause cooling and drying around the North Atlantic, and more importantly would probably weaken the Indian monsoons and the West African monsoons, with potentially dire humanitarian implications. For 4ºC, models suggest that the chance of collapse is 1-5%, though they probably understate the risk. 

There is deep uncertainty about potential sea level rise once warming passes 3ºC. For higher levels of warming, there is a risk of non-linear tipping points, such as collapse of the West Antarctic Ice Sheet, which would cause sea levels to rise by around 5 metres over 100 years, which would probably cause flooding of numerous highly populated cities, especially in Asia. 

Due to progress on emissions, these tipping points now look less likely than they did ten years ago, but their expected costs (impact weighted by probability) may still be large. Furthermore, our understanding of the climate system is imperfect, and there may be other damaging tipping points that we do not yet know about. 

All this being said, contra some prominent research, the evidence from models and the paleoclimate (the deep climate history of the Earth) suggests that it is not the case that, once warming passes 2ºC-4ºC, runaway feedback loops will kick in that make the world uninhabitable. 

Direct impacts fall well short of human extinction

Given progress in emissions, the risk of human extinction from the direct effects of climate change now seems extremely small. The most plausible route to human extinction is via runaway feedback loops. However, models and evidence from the paleoclimate suggest that it is impossible to trigger such runaway effects with fossil fuel burning. Models suggest that we could only trigger a runaway greenhouse if CO2 concentrations pass 3,000ppm (at the very least), which is out of reach on revised estimates of recoverable fossil fuels. 

Moreover, global average temperatures have been upwards of 17ºC higher several times in the past without triggering runaway feedback loops that killed all life on Earth. Indeed, since the Cretaceous, 145 million years ago, periods of high temperatures and/or rapid warming have not been associated with ecological disaster. However, prior to the Cretaceous, climate change was linked to ecological disaster. In the report, I discuss the theory that this was because of ecological and geographical factors unique to the pre-Cretaceous period. 

I construct several models of the direct extinction risk from climate change but struggle to get the risk above 1 in 100,000 over all time. 

One argument that climate change could directly cause civilisational collapse is that it could be a contributing factor (along with deforestation, human predation, and pollution) to ecosystem collapse, which could in turn cause the collapse of global agriculture. I argue in the main report that this risk is minimal.

Indirect risks are under-researched but now seem fairly low

Because interstate war has become increasingly rare since the end of World War II, most of the literature on climate change and conflict has focused on the connection between climate and civil conflict: conflicts between a government and its citizens in which more than 25 people are killed. 

Scholars in the field agree that, so far, climate-related factors have been a much weaker driver of civil conflict than other factors such as socioeconomic development and state capacity. However, there is strong disagreement in the field about how important climate change will be in the future. It is widely agreed that the risk of climate-induced conflict is greatest in low- and middle-income countries, and that the most important mechanism is damage to agriculture. 

The potential impact of climate change on the risk of interstate, rather than civil, war is potentially much more important but also much less studied. Among interstate conflicts, conflicts between the major powers pose by far the largest risk to humanity. This is because the major powers have far more destructive weaponry and have the capacity to alter the trajectory of humanity in other ways. 

The most plausible way that climate change could affect the risk of interstate war is by causing agricultural disruption, which causes civil conflict, which in turn causes interstate conflict. Indeed, there is some evidence that countries embroiled in civil conflict are more likely to engage in military disputes with other countries. 

It is difficult to see how climate change could be an important driver of some of the most potentially consequential conflicts this century - between the US and Russia, and the US and China. It is more plausible that climate change could play a larger role in driving conflict between India and Pakistan and also India and China. However, for plausible levels of warming, other drivers of this conflict seem much more important. 

It is extremely difficult to provide reliable quantitative estimates of the risk of Great Power War caused by climate change. Nonetheless, I have built a model that attempts to put some numbers on the key considerations. I think this is valuable for several reasons. Firstly, it clarifies the cruxes of disagreements and allows focused discussion on those cruxes. Secondly, it allows us to prioritise different problems. If we do not quantify, we will still have judgments about how important different considerations are. Models make these considerations precise. 

The downside of quantitative models is that they can cause false precision and anchor readers, even if the model is not good and has not been subject to scrutiny. Many of the considerations I have discussed are very difficult to quantify because there is essentially no literature on them.

With those caveats in my mind, my best guess estimate is that the indirect risk of existential catastrophe due to climate change is on the order of 1 in 100,000, and I struggle to get the risk above 1 in 1,000. Working directly on US-China, US-Russia, India-China, or India-Pakistan relations seems like a better way to reduce the risk of Great Power War than working on climate change. 

My personal thoughts on prioritising climate change relative to other problems 

My primary goal in this report is to help people to answer the following question:

If your goal is to make the greatest possible positive impact on the world, what should you do with your time and money right now, given how the rest of society is spending its resources?

Crucially, this question is about what people should do on the margin. It is about what people should do given how society allocates its resources, not about how society as a whole should allocate its resources. Thus, when I say that working on some other problems, such as nuclear war or biosecurity, will have greater impact, this doesn’t mean that society as a whole should spend nothing on climate change and everything on nuclear war and biosecurity. Rather, it is a claim about what we should do with our resources given how other resources are currently spent. 

Moreover, the question I am trying to answer in this report is specifically about how to make the greatest possible impact on the world. This is the highest possible bar. In my view, climate change is one of the most important problems in the world, but other problems, including engineered viruses, advanced artificial intelligence and nuclear war, are more pressing on the margin because they are so neglected. One can visualise this in the following way. Green projects are beneficial on the margin, and red projects are harmful on the margin. Deeper green projects are more beneficial whereas deeper red projects are more harmful on the margin. 

To emphasise, we should not confuse the claim that other problems are more pressing than climate change with the claim that climate change doesn’t matter at all. I am glad that climate change is a top priority for millions of young people and for many of the world’s smartest scientists, and I would like governments and the private sector to spend more on climate change. I helped to set up the Founders Pledge Climate Change Fund (donate here), which has helped to move millions of dollars to effective climate change charities. The point is that I would like other global catastrophic risks to receive comparable attention, not that I would like climate change to receive less than it does today. 

Imagine that only a few hundred people in the world thought that climate change is an important problem (rather than at least tens of millions), that philanthropists worldwide spent a few million dollars a year on climate (rather than $10 billion), that society as a whole spent a million dollars on the problem (rather than $1 trillion), and that the international institutions trying to tackle the problem either don’t exist or have a similar budget to a McDonald’s restaurant. How bad would climate change be? This is how bad things are for the other global catastrophic risks, and then some. 

The final important piece of context is as follows: although I am taking a longtermist perspective in this report, my conclusions about the priority of climate change relative to other global catastrophic risks are also true if you think only current generations matter. In my view, the risks from AI, biorisk and nuclear war this century are much higher than commonly recognised. 

  • AI: Forecasters on the community forecasting platform Metaculus think that artificial intelligent systems that are better than humans at all relevant tasks will be created in 2042. The most sophisticated attempt to forecast transformative AI is by Ajeya Cotra, a researcher at the Open Philanthropy Project and her model now suggests that it is most likely to be developed in 2040. A 2017 survey of hundreds of leading AI researchers found that the median judgments implied that there is around a 4% chance of human extinction caused by AI before the end of the century.
  • Biorisk: Combined forecasts on Metaculus imply that the chance of synthetic biology killing more than 10% of the world population by 2100 is around 7%. The implied chance of synthetic biology killing more than 95% of the world population before 2100 is around 0.7%.
  • Nuclear war: Forecasters on the community forecasting platform Metaculus think that there is an 8% chance of thermonuclear war by 2070.

These risks are not speculative possibilities, and the case for working on them is not contingent on ignoring the suffering of the current generation for the sake of a tiny probability of techno-catastrophe. I think it highly likely that my daughter will have to live through nuclear war, pandemics created by engineered viruses, and/or the emergence of transformative AI systems that will radically alter society. It is deeply unfortunate that few people acknowledge these problems, and that many people who are aware of them dismiss them as sci-fi fantasies without attempting to engage with the arguments, or grappling with the fact that many people working in these fields agree that the risks are large. 

Although, I contend, my conclusions follow on both neartermist and longtermist perspectives, it is important to reiterate that, in my view, a longtermist ethical point of view is the correct one. I see no compelling arguments for ignoring the welfare of future generations, and an ethical system that does ignore them is obviously difficult to square with concern about climate change. 

While many people accept that the direct risks of climate change are lower than these other risks, some argue that the indirect effects of climate change may be large enough to make the total risk of climate change comparable. I do not think this is plausible. As discussed above, my rough models suggest that the total risk of climate change falls well short of the direct risk posed by the other global catastrophic risks. Moreover, the other risks also have indirect effects. As a rule, we should expect greater direct risks to have greater indirect effects. For instance, the indirect effects of trends in biotechnology seem to me much larger than the indirect effects of climate change. If biotechnology does democratise the creation of weapons of mass destruction, the indirect effects for the global economy and geopolitics are hard to fathom but seem enormous. 

Overall, because other global catastrophic risks are so much more neglected than climate change, I think they are more pressing to work on, on the margin. Nonetheless, climate change remains one of the most important problems from a longtermist perspective. If progress stalls and emissions are much higher than we expect, then there is a non-negligible chance of highly damaging tipping points. Moreover, climate change is a stressor of political upheaval and conflict, which can in turn increase other global catastrophic risks. Finally, extreme climate change would make recovery from civilisational collapse more difficult.

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Here are my high-level thoughts around the comments so far of this report:

  • This is a detailed report, where a lot of work has been put in, by one of EA's foremost scholars on the intersection of climate change and other global priorities.
  • So it'd potentially be quite valuable for people with either substantial domain expertise or solid generalist judgement to weigh in here on object-level issues, critiques, and cruxes, to help collective decision-making.
  • Unfortunately, all of the comments here are overly meta. Out of the ~60 comments so far on this thread, 0.5 of the comments on this thread approach anything like technical criticism, cruxes, or even engagement.
  • After saying that, I will hypocritically continue to follow the streak of being meta while not having read the full report.
  • I think I'm confused about the quality of the review process so far. Both the number and quality of the reviewers John contacted for this book seemed high. However, I couldn't figure out what the methodology for seeking reviews is here.
    • T
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Unfortunately, all of the comments here are overly meta. Out of the ~60 comments so far on this thread, 0.5 of the comments on this thread approach anything like technical criticism, cruxes, or even engagement.

I think this is mainly because of the length of the report which makes it hard to make meaningful critiques without investing a bunch of time

Yes, and I note that as/after I wrote my comment, there are more thoughtful object-level comments. So perhaps I commented too early and should've just waited for people to have time to read the report first and then provide object-level comments!

Not sure why this was downvoted. I really appreciate comments where people publicly acknowledge they may have made an error and update their views. 


I think this is a good place to have discussions about claims in specific sections (rather than the whole report) if people would like

Hi, John.

I don't have time in the next several days to give your write-up the attention it deserves, but I hope to study it as a learning opportunity and to expand my grasp of general arguments around what I call steady-state climate change, that is, climate change without much contribution from tipping points this century and without strong impacts at even higher temperatures (eg., 3-4C). I appreciate the structure of your report, by the way, it lets a reader quickly drill down to sections of interest. It is clearly written. 

At the moment, I am considering your analysis of permafrost and methane contributions to GAST changes. I have a larger number for total carbon in permafrost than you, 1.5Tt carbon, but now have to go through references to reconcile that number with yours. Your mention of an analysis from USGS deserves a read through articles from the reference you gave, and I am attempting that now. 

There are several parameters involved (only some independent), to do with:

  •  source type (anearobic decomposition, free gas deposit, methane hydrate dissolution),
  •  source size, 
  • source depth and layering, 
  • rate of release (obviously dependent on other param
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Hi Noah, 

(Just noting that I'm not ignoring your comments about methane clathrates, but I don't think you were asking for a response there, but were instead just highlighting some issues for you to look into? Correct me if I'm wrong)

Yes I note that there is deep uncertainty about sea level rise once warming passes 3ºC and that sea level rise might be much higher than estimated. I discuss the impacts this might have in the sea level rise section and the economic costs section

I agree that many specific tipping points haven't made their way into IPCC models

Noah Scales
Hi, John. In your research report, you wrote: and you include the footnote: In the Nature paper you cited for a listing of permafrost carbon, you find the following quote on the same page as lists total carbon in the top 3 meters of permafrost. I  list the geographic regions in braces for clarity:  So a total amount of carbon in permafrost between 1730-1980 Pg, or 1.73-1.98 trillion tonnes of carbon, not the 1 trillion tonnes you list. This is typically described as being twice the carbon currently in the atmosphere, but how quickly it causes heating given some rate of thaw depends on whether it is released as methane or carbon dioxide. As you know, methane has 100X the heating potential of carbon dioxide, but that drops off rapidly over a couple decades, so rate of release is very important. If you look elsewhere for amounts, you find the usual figure listed is 1.5Tt for total carbon in permafrost. I think that represents updates to estimates but have not looked into it in detail. A slight rephrase of your sentence "About 1 trillion tonnes of carbon is stored in permafrost." to either mention the top 3 meters of soil explicitly for the trillion tonnes number or to use some figure closer to 1.5Tt (NOAA's mid-range for total northern permafrost). will bring the announced total closer to what people typically mean by total carbon in permafrost, just the permafrost in the North.  Earlier in the same Nature paper, you read: For the reference you cite, it's clear that carbon deeper than 3m is considered "susceptible to future thaw", and so is relevant to discussions of permafrost contribution to global warming. In fact, some existing examples of that thaw are mentioned in that 2015 paper. I think there are numerous taking off points for discussion of the effects of permafrost thaw aside from the box 5.1 sections of the IPCC technical report that you cite.  The parameters deciding the effects of permafrost include: * abrupt vs gradual release of carbon * carbo
Noah Scales
Right, I wasn't looking for a response about methane, more just excitedly listing, I guess. My motivated thinking, going in, is that there's plenty of exposed methane hydrates and free methane on shallow parts of the continental shelves exposed to much warmer waters in the Arctic and Siberia. A Nature paper from Ruppel is a bit old, and includes discussion of deeper deposits in warmer waters much further south. The paper does make exceptions for shallower deposits, as in the Arctic sea. She notes technical difficulties in resolving the origin of the methane even in those cases, but there's been efforts to resolve the questions since then. A later Reviews Of Geophysics paper  confronts predictions about sources and distributions.I have to dig into that.  Carolyn Ruppel is also a proponent of drilling undersea methane for fuel, and has been for the last decade. Treatment of the melting arctic as a tipping point seems politically unpopular, now that various projected benefits of its melt have been identified. We can drill for natural gas or oil, fish, establish shipping lanes, or fight over sovereignty up there, but I'm not seeing much government attention on the ice-free Arctic as an actual climate problem.  Still, Ruppel holds an important position, and I will give her research more attention now. Thank you. Yes, as far as sea level rise, I read the sections you mentioned, thank you. The West Antarctic is less of an immediate concern than Greenland, so I am puzzled why you haven't mentioned Greenland explicitly. Your discussion of sea level rise doesn't include Greenland's contribution, but Greenland will melt before the West Antarctic, and it holds several meters of sea level rise in its ice. I believe that Greenland's melt could shutdown the AMOC as well. I think processes like fires on permafrost land go ignored in models of permafrost thaw, just like lubrication of the bottom of Greenland Ice goes ignored. Some discussions about climate change suggest that pe
Guy Raveh
Strongly upvoted. Usually I would've given a regular upvote, but I think this should be highlighted above the meta comments and flame wars.
Noah Scales
Thanks, I'm actually surprised that members of the community have such energy around its concerns about the quality of climate change scholarship. I didn't expect that that the OP would generate these concerns.  I posted a radical opinion about climate change here some time back that got a few downvotes and almost no readers. Basically, I think global warming is now self-amplifying. Anyway, I don't mind the lack of interest, it wasn't scholarly work.   The meta comments are about research process, how best to represent differing viewpoints, and whether John gave fair weight to considerations outside the point of view that John holds. I don't have a comment here, I think I'll take what was given as where to start my own learning efforts.  What I would like from others who post here is more engagement around specific scenarios of risk. From my review of comments made in discussions of climate change, the obstacle seems to be lack of commitment to the plausibility of specific scenarios.  So for example, a discussion of a multi-breadbasket failure would include a few sentences about how our civilization would respond by choosing to grow its own food, eg., in cities. I would like to see someone work that through. We're talking about locally producing calorie-dense sources of carbohydrates and proteins in a situation in which grain stocks become limited worldwide. Vegies on your windowsill won't do the job. More generally, there's a question about stocks vs flows, we have some grain reserves, but how much, and how should they be managed in case of what percentage of global crop failures? George Monbiot has some conclusions (hint, he wants to use some old NASA tech), I'm looking forward to reading his work. Then there's the reason for failure. Hurricanes inundating low-lying farm areas (like Vietnam) would have a longer impact on soil productivity than would a 6-week heat wave, or would it? Another example would be how we handle internal and global migration, given so
Thanks for mentioning ALLFED. We do tend to focus on nuclear winter, including with NASA tech like hydrogen single cell protein. However, a lot of the foods we research are relevant to climate catastrophes such as multiple breadbasket failure, including seaweed.
Noah Scales
Yes, the protein production technology is certainly relevant. I don't think the seaweed is unless you are confident that it would survive various changes in ocean temperature, acidity, pollutant levels, flora, and fauna that progress with climate change. What do your models say?
We have not modeled seaweed growth in a warming world, but I believe others have. I expect that species would need to move to higher latitudes, as they would need to move to lower latitudes in the case of nuclear winter.
Noah Scales
What geographic range would growth of the seaweed serve depending on what forms of food transport? Is the use of seaweed as a food source likely restricted to the coasts and coastal populations?
Seaweed can be dried and transported long distances. It can also be used for reducing climate change, including sequestering CO2 and reducing methane emissions of cattle.
Noah Scales
Can it be grown in tanks? I think fallout from a nuclear war would contaminate all open areas used for agriculture, including the oceans, for example, from fallout on winds, dust, rain (if there is any?), or water contamination carried on ocean currents. Do your models suggest that agriculture and aquaculture and use of open areas is a strong contamination risk or no? In the case of climate change, the major shifts are in pH, local heat, currents, and ecology. I suspect strong climate change will require tank growth of seaweed, if any. There are global models of ocean pH change. I think pH is lower at the poles while absolute water temps near the coasts will be higher at the equator. There was an algae-based oil called Thrive, totally monounsaturated, if I remember right, that until recently was commercially available. I used it several times and liked it as a salad oil.
Seaweed can be grown in tanks, and so can microalgae. But from what I've seen, the cost is significantly higher in tanks. Radioactive contamination is a concern, especially in target countries. But it is likely not the most important concern, as Hiroshima was continuously inhabited. Radioactive contamination would be diluted in the oceans, so I think seaweed would be better than land crops in this regard.
Noah Scales
Hi, Dr. Denkenberger Thanks! I appreciate your thoughts. I have a few more questions: 1. If you can find the research about seaweed growth in lower-pH conditions with heat waves in nearshore waters, and changes in nutrient availability (probably declines), I want to know more. I think seaweed might be a good near-term choice of replacement agriculture in the next 10-20 years, but during that time, it makes sense that the world scale up the kinds of food sources that you and ALLFED explore. 2. I like dextrose monohydrate, as a food product, it's widely available and dissolves clean in water. With flavoring and in combination with whey (and of course casein, but I really favor whey), it makes a replacement milk. I understand that anhydrous dextrose has different properties in foods. What form of dextrose would paper mills produce? Are you more thinking something with less sweetness, like maltodextrin (also a possibility in a milk substitute)? Could the mills produce different types of carbs? 3. Assuming a 2400 kcal diet, what are your targets for macronutrients? Given a source of concentrated carbohydrates, people need a protein source, a fat source, and additional sources of minerals and vitamins and other compounds. I  lik carbs (510g-450g), proteins (40g-100g), and an EFA source (1g-10g), but that's just me. Adding in fats, you need to choose a carb minimum, as I think the trade-off would be carbs for fats, not proteins for fats.  There's a variety of reasons to choose different kcalorie totals and macronutrient balances, do you have a list of your criteria and final decisions or have you looked into that in detail? 4. Have you looked into the manufacture of: * individual essential amino acids? * essential fatty acids? * vitamin and mineral supplements? 5. Based on UN studies, there's a lower limit on protein consumption that maintains protein balance in a person[1]. Has ALLFED chosen a minimum daily human EAA requirements, per kg bodyweight, and something si

Imagine that only a few hundred people in the world thought that climate change is an important problem (rather than at least tens of millions), that philanthropists worldwide spent a few million dollars a year on climate (rather than $10 billion), that society as a whole spent a million dollars on the problem (rather than $1 trillion), and that the international institutions trying to tackle the problem either don’t exist or have a similar budget to a McDonald’s restaurant. How bad would climate change be? This is how bad things are for the other global catastrophic risks, and then some. 


This seems to overstate how bad the situation is (although qualitatively it remains an absurd underinvestment, with painfully low-hanging fruit to avert pandemics and AI catastrophe at hand). Surveys of the general public and area experts do show substantial percentages in the abstract endorse nuclear (in particular), bioweapon, and AI risks as important problems (as you mention later). Governments wage wars and spend very large amounts of attention and resources on nuclear proliferation and threats. Biodefense has seen billions of dollars of spending, even if it was not well-crafted to reduce catastrophic bioweapon risk. The low budget for the BWC is in significant part a political coordination problem and not simply a $ supply issue. Annual spending from Open Philanthropy and the Future Fund on catastrophic risks, with priorities close to yours, is now in the hundreds of millions of dollars.


These are good points, I will amend

Didn't separate karma for helpfulness and disagreement (frequently used on LessWrong) get implemented on the EA forum recently? This post feels like the ideal use case for it:

  •  There are some controversial comments with weakly positive karma despite lots of votes, where I suspect what's going on is some people are signalling disagreement with downvotes, and others are signalling 'this post constitutes meaningful engagement' with upvotes. 
  • There are also some comments where the tone seems to me to be over the line, with varying amounts of karma (from very positive to very negative), from various people.  

Were a two-karma system available, I think I would use both [strong upvote, strong disagree] and [strong downvote, strong agree] at least once each.

Will Aldred
I notice a two-karma system has been implemented in at least one EA Forum post before, see the comments section to this "Fanatical EAs should support very weird projects" post.
the forum did offer the chance of having agree/disagree on the post, I just forgot to respond. I think it is a beta feature but happy for it to be used on this post
I think we also need renewed discussion of how the karma system contributes to groupthink and hierarchy, things that, to put it gently, EA sometimes struggles with somewhat. As far as I can tell, the system gives far more voting power to highly-rated users, allowing a few highly active (and thus most likely highly orthodox) forum users to unilaterally boost or tank any given post. This is especially bad when you consider that low-karma comments are hidden, allowing prominent figures (often with high karma scores) to soft-censor their own critics. This is especially worrying given the groupthink that emerges on internet fora, where a comment having a score of -5 makes it much more likely for people to downvote it further on reflex, and vice versa. I am not going to go into details here beyond saying that this is the plot of the MeowMeowBeenz episode of Community. MeowMeowBeenz does not contribute to good epistemics.

I disagree that the problem here is groupthink, and I think if you look at highly rated posts, you can't reasonably conclude that people who criticise the orthodox position will be reliably downvoted. I think the problem here is that some people vote based on tone and some on content, which means that when something is downvoted different people draw different conclusions about why.

I think the problem here is that some people vote based on tone and some on content,

I hope to encourage more people to instead upvote based on rigor/epistemics/quality on the margin, rather than based on tone or based on agreement (which is some of "content") or vibe. 

EDIT: I also think a surprisingly high number of people upvote low-quality criticisms that have a good tone, which makes me surprised when others assert than the movement is systematically biased against criticisms ("insufficient discernment" will be a fairer criticism, but that's a mistake, not a bias).

Phil Tanny

I frequently catch myself, and I'm embarrassed to admit that, being more likely to upvote posts of users that I know. I also find myself anchoring my vote to the existing vote count (if a post has a lot of upvotes then I am less likely to downvote it). Pretty sure I'm not the only one.

Furthermore, I observe how vote count influences my reading of each post more than it should. Groupthink at its best.

I suspect if the forum hid the vote count for a month, there would be significant changes in voting patterns. That being said, I'm not sure these changes would actually influence the votesorted order of the postings - but they might. I suspect it would also change the nature of certain discussions.

Phil Tanny
Admirable honesty, well done.  
Guy Raveh
Why was this downvoted?
Phil Tanny
Phil Tanny

The dynamics in this post seem weird. John is very well-respected within EA for his work on climate change, and having this report commissioned by Will makes it even more likely to be disseminated quickly and widely throughout the community.

In my opinion that means it's particularly essential that thoughtful critiques are brought up earlier rather than later. Of course the report has already been reviewed by a lot of people I respect, but in general I'm in favour of people asking questions and raising concerns here, even though I would expect most concerns to have already been thought about and be relatively easily addressed, or in some cases not worth addressing.

So I'd like to encourage people to post these questions, concerns and critiques, but I think the environment in these comments hasn't always been encouraging. People have been significantly downvoted for reasons I don't understand, and John has in one case accused someone of misrepresenting their identity which I don't think was helpful.

Do people agree with me that we should encourage people to post their questions and concerns here, even if you don't agree with the specific questions? Do people agree the current environment isn't ideal for that?

I didn't downvote any of the criticisms but I can understand why people would downvote the following quote as it is quite close to assuming  intention:

"Either you are aware that this characterisation is highly inaccurate and unfair, or you are not. If the former, I am disappointed by your (apparent) dismissiveness and willingness to mischaracterise."

I've seen every question or critique be below zero at some point in the last 24 hours, not just one!

Strong upvote, I thought I was going crazy. Thank you!

Thank you for doing this and congratulations! 

I haven't managed to read the full report yet unfortunately, but I have a few questions/criticisms already- sorry to move onto these so quickly, but nonetheless I do think its important. (I tried to write these in a more friendly way, but I keep on failing to do, so please don't take the tone as too aggressive, I am really not intending it to be, it just keeps coming across that way ! Sorry (: ) :

  • There are no mentions of systemic or cascading risks in the report. Why is this?
  • You don't seem to engage with much of the peer-reviewed literature already written on climate change and GCRs. For example: Beard et al 2021, Kemp  et al 2022, Richards et al 2021. Don't get me wrong, you might disagree or have strong arguments against these papers, but it seems to some degree like you have failed to engage with them
  • You don't seem to engage with much of the more complex systems aspects of civilisation collapse/ existential risk theory. Why is this?
  • There are no mentions of existential vulnerabilities and exposures, and you seem to essentially buy into a broadly hazard based account. The subdivision into direct and indirect effects further s
... (read more)

Hello Gideon

  • I don't think explicit discussion of cascading risks would change the fundamental conclusions, and cascading risks are implicitly discussed at several points in the piece. 
  • I have read the papers you mention. You will find (attempted) refutations of many of the points in those articles scattered across the report. In earlier drafts, I did have a direct response to those papers, but it is now all dealt with in different sections of the main report. 
  • I don't agree with the 'everything is connected' idea of society, such that society is incredibly sensitive to mild climatic changes. If that is what you mean by complex systems theory. And I defend that view at length in the report. 
  • There are many many different ways of conceptually dividing up an analysis of climate risk. The direct/indirect way is conceptually exhaustive and so insofar as I have accurately covered the direct/indirect risks, I have accurately covered overall climate risk
  • True that I did ignore this, explicitly at least. I do not see how it would affect my conclusions. There is no indication from the climate literature that climate change would cause anything close to a boring apocalypse. Also, I
... (read more)
(I have a few thoughts on this but it’s being marked as spam for some reason, possibly length. I’m going to post this as a short response and then edit in the content. Please let me know if you can see it.) Hi John, thanks for the post! I'll leave an in-depth response to Gideon, but I have a few points that I think would be helpful to share. In short, your response worries me. I have tried to keep the prose below inoffensive in tone, but there is a trade-off between offensive directness and condescending obfuscation. I hope I have traced the line accurately.  * You may not think significant discussion of cascading risks would change the fundamental conclusions of your report, but many researchers, often those with considerably more experience and expertise in climate risk (e.g. the IPCC), do: strongly so. Surely in a book-length report there is room for a few pages? * If you have refuted arguments, is it not academic best practice to cite the papers you respond to? In any case, if you know of and have read the papers, are we to understand that you believe many (if not most) peer-reviewed papers on Global Catastrophic and Existential climate risk are not worth mentioning anywhere in 437 pages of discussion? * This response causes me the most concern. That is simply not what complex systems theory is. Either you are aware that this characterisation is highly inaccurate and unfair, or you are not. If the former, I am disappointed by your (apparent) dismissiveness and willingness to mischaracterise. If the latter, I wonder how you could have done anything close to sufficient research into one of the foundational components of many studies of climate risks. * It is true that there are many conceptual frameworks for climate risk, and in a study of any topic you are generally expected to state, explain, and justify your conceptual framework. This is especially true when the framework you use (i.e. that of the Techno-Utopian Approach) has been strongly critiqued, for

The work was reviewed by experts, as I discuss in the other comment. 

  • I do discuss tipping points at some length. I don't see how the idea of cascading risks would change my substantive conclusions at all. If you want to argue that cascading risks would in fact affect my conclusions, I would be happy to have that debate.
  • In fairness to me, the Kemp et al paper was only published a couple of weeks ago, so I couldn't include it in the report. I think much of that paper is incorrect, and the reasons for that are discussed at length in the report. The conclusions of the Beard et al and Richards et al paper are, in my view, refuted mostly in section 5 of my report. If you have a criticism of that section, which largely leans on the latest IPCC report, I would be happy to have that discussion
  • I have read the Richards et al complex systems paper. It contains the following diagram purporting to show how climate change could cause civilisational collapse

I am open to the possibility that my argument that climate change will not destroy the global food system is wrong. I am happy to discuss substantive criticisms of those arguments. I do not see one in the Richards paper, or in what you hav... (read more)

Given the review process was not like normal peer review, would it be possible to have a public copy of all the reviewers comments like we get with the IPCC. This seems like it may br important for epistemic transparency

Indeed, knowing what I know of some of the reviewers Halstead named I am very curious to see what the review process was, what their comments were, and whether they recommended publishing the report as-is. I've always been quite confused about attitudes to scholarly rigour in this community: if the decisions we're making are so important, shouldn't we have really robust ways of making sure they're right?
About planetary boundaries: Leaving aside the discussions on the specific value and/or variable used to measure a specific boundary -which the authors themselves caveat that may be temporal until finding better ones-, isn't most of the controversy due to critiques conflating planetary boundaries and tipping points?

I respect this for being a substantive critique and have upvoted, even though it does read as pretty harsh to me.

I do think the way this comment is written might make it hard to respond to. I wonder if it would be easier to discuss if either (a) you made this comment a separate post that you linked to (it's already long enough, I reckon) or (b) you split it into 3-4 individual comments with one important question or critique in each, so that people can discuss each separately? My preference would be for (a) personally, especially if you have the time to flesh out your concerns for a less expert audience!

I was worried about the harshness aspect but to be frank there are only so many ways to say that someone in a position of power and influence has acted with negligence. Perhaps these could also be useful things to do (thought given the afore-mentioned herd-downvoting I doubt that (a) would receive sufficient good-faith engagement to be worth writing. (b) could be useful for facilitating small-scale discussion, but I haven't seen any indication that there are people who want to or are trying to do that, e.g. with a comment saying 'On point #4...' In any case, I have seen far longer comments than mine and comments with more questions and less elaboration than Gideon's get dozens of upvotes before. These criticisms (and I'm discussing both your response and Karthik's here, as well as a more general pattern) appear to only be brought up when the EA big boys are being criticised: I doubt if Gideon had asked five complimentary questions he would have received anything close to such a negative reaction. This does remind me of a lot of the response to Democratising Risk: Carla and Luke were told that the paper was at once too broad and too narrow, too harsh and yet not direct enough: anything to dismiss critique while being able to rationalise it as a mere technical application of discursive norms.
It seems like my concern was unwarranted anyways as John already responded directly to each of your points!
Yes and no in my opinion haha but I see your point
I'm interested to see your in depth response to me
I meant 'I'll leave the in-depth response to Gideon'. What you say speaks for itself: if Halstead presented this at a climate science org these would be some of the first questions asked and I'm puzzled (+ a bit weirded out, to be frank) as to why they're getting such a hostile response.
(Case in point for my comment about downvoting,  community hierarchy, and groupthink, below) 

I strongly upvoted this because it was at -4 karma when I saw it and that seems way too low. That said, I understand the frustration people feel at a comment like this that would lead them to downvote. It raises far too many questions for the OP to answer all at once, and doesn't elaborate on any of them enough for the OP to respond to the substance of any claim you make. This is the kind of comment that is very hard to answer, regardless of its merit.

Perhaps that's fair, certainly the asking too many questions part. I am less sure that it doesn't expand enough, because I would like to give John credit to suggest he knew what bits of the literature he was excluding. More generally, I think my concern is a post like this may quickly establish itself as "orthodoxy" so I wanted to raise my concerns as early as possible, but perhaps I should have waited a bit of time to do a more comprehensive response. Perhaps I will learn for next time

To be fair a 'comprehensive' response would include even more questions, so I'm not confident there's any way to win here.

Yes I am also very worried about the orthodoxy point; EA is often a closed citation loop, where a small number of people and organisations cross-cite one another and ignore outside ('non-value aligned') work. Most reading lists are absolutely dominated by ~5 names, sometimes a few more.

Halstead, as  a semi-big name at a prominent organisation (and, for better or worse, the movement's de facto authority on climate change) is extremely likely to have his work accepted into the canon without significant challenge from climate experts (with training in climate science and policy, rather than philosophy...).

Thus, a fresh crop of undergraduates on will be told that climate is no big deal compared to sexier and more EA-friendly stuff like AI without ever being aware of all the climate-related GCR work Halstead doesn't engage with (or even mention). I suspect, perhaps uncharitably, that this is because most of it disagrees with him. This in turn is partially because it has to be peer-reviewed by people selected on the basis of their expertise in climate risk, rathe... (read more)


The report was reviewed by various people with expertise in various different aspects of climate change. The reviewers are pasted at the bottom of this comment. 

The criticism raised by GIdeon seems to be that it doesn't cite some studies that take an extreme stance on climate risk relative to mainstream climate scientists and climate economists.  I discuss many of the claims made in these papers at considerable length. If you disagree with some of my substantive claims, then I would be happy to discuss them. 

I don't think my report is outside the mainstream of IPCC science. I can't think of any substantive claims that are inconsistent with the latest IPCC report, with the exception of my criticism of the Burke et al (2015) paper and the ecosystem collapse stuff.

The reviewers for the report are below, though they may not agree with everything I have written. 

  • Matthew Huber, Professor, Dept. of Earth, Atmospheric and Planetary Sciences, Purdue University
  • Dan Lunt, Professor of Climate Science, Bristol University
  • Jochen Hinkel, Head of Department of Adaptation and Social Learning at the Global Climate Forum 
  • R. Daniel Bressler, PhD Candidate in Economics at Columb
... (read more)
This is good, though offering comments on various sections of a google doc is of course a very different exercise to full and blind peer-review. Did any of the reviewers notice that you had not mentioned (almost?) any climate-related GCR papers? If so, what was your response to them? As per your comments about complex systems above, please do not dismissively mischaracterise the views of your critics. This is the kind of thing an average forum user would get hammered for, please do not try to get away with it just because you know you can. If you discuss their arguments, why didn't you cite them? If the X-risk climate corpus takes an 'extreme' stance by and large, is that not the kind of thing you would expect to see discussed in a >400 page report on climate change X-risk? Even to the extent that this report is within the IPCC mainstream, notwithstanding, for instance: * The complete absence of systems perspectives (even just to justify your rejection, something I, to be frank, would expect in an undergraduate dissertation) * Lack of consideration of vulnerability, exposure, or cascading disasters * Silent disregard for Reisinger et al.'s discussion of the concept of risk ...it is well-known that the IPCC must moderate its conclusions and focus on better-case scenarios for political reasons, i.e. so as to not be written off as alarmist. You know this, because it is mentioned in Climate Endgame and discussed at length by Jehn et al. This is another rather important issue in climate risk scholarship you would expect to see mentioned in a work this long.

"it is well-known that the IPCC must moderate its conclusions and focus on better-case scenarios for political reasons, i.e. so as to not be written off as alarmist"

As a climate scientist reading this, I just thought I'd pick up on that and say I have not got that impression from reading the reports or conversations with my colleagues who are IPCC authors. I've not seen any strong evidence presented that the IPCC systematically understates risks - there are a couple of examples where risks were perhaps not discussed (not clearly underestimated as far as I've seen), but I can also think of at least one example where it looked to me like IPCC authors put too much weight on predictions of large changes (sea ice in AR5). (This is distinct from the thought that the IPCC doesn't do enough to discuss low-likelihood, high-impact possibilities, which I agree with.)

It might be good to zoom out here and get a sense of what the criticism is here. I am being criticised for not citing four papers. One of them is by you and Kemp, is not peer-reviewed and is not primarily about climate change. The other one is Kemp et al 2022 which was published two weeks before I published my report so I didn't have time to include discussion of it. The other papers I am being criticised for not mentioning are Beard et al and Richards et al. If you want to explain to me why the points they raise are not addressed in my report, I would be happy to have that discussion.  The Jehn et al papers make claims which are  wrong. It is blatantly not true to anyone who knows anything about climate change that the climate science literature ignores warming of more than 3ºC. 

I can see where you're coming from here but I don't think the specifics really apply in this case.

There are many questions to raise about this google doc, and it seems fair to the reader to ask them all in one place rather than drip-feeding throughout a tree of replies and reply-replies. If responding to them all would take up too much of Halstead's time, he can say so, no?

There's not usually very much to elaborate when it comes to questions of omission: x is an important aspect of climate risk, Halstead has not mentioned x.

I suppose you could add the implicit points (studies of topics should include or at least mention the important aspects of those topics, space wasn't a constraint, Halstead  knows what the terms mean, etc.) but that's unnecessary in 99% of conversations and not a standard we expect anywhere else.

(Edit: it seems my fears were right, lol)

Thanks for posting this Gideon, I shared similar issues to you but didn't make a reply because I feared the it would would be dismissed or ignored. It is gratifying to see that John has replied, but epistemically concerning that your entirely reasonable criticisms are being so heavily downvoted: at present you average 1 point from 13 votes.

These are critiques you would expect anyone with a background in climate risk to make and I don't see any good reason for them to have been dismissed by so many fellow EAs. Could any of the downvoters explain their decision?

Phil Tanny

Great to see such a detailed, focused, and well-researched analysis of this topic, thank you. I haven't yet read beyond the executive summary yet other than a skim of the longer report, but I'm looking forward to doing so.

Hi John

Given the degree to which you have highlighted how experts have commented and reviewed the piece, will you, for the sake of intellectual transparency, commit to publishing all this expert feedback like the IPCC does. I think this may really help. 

I said this in a subcomment, and it (worryingly) got significantly downvoted. It is a worrying sign for a community if a call for intellectual transparency (which is a key norm in EA) is downvoted just because the writer (ie me) has been critical of the piece.

I have great respect for you as an academic and an EA, and I trust that you will agree that such intellectual transparency is a useful norm, and if possible commit to publishing the commentsand reviews that those who reviewed the publication sent! The worry in the above paragraph is certainly not directed at you, and I have all the confidence that you are and will remain committed to maintaining EA as an as transparent space as possible

All the best



I will ask the experts if I can share their feedback. I did ask a couple of them to do this but after a long review process they didn't respond so I decided not to ask the other experts if I could share theirs as I thought it would be weird to have comments on some parts but not others. Maintaining interest in the process from experts can be difficult because they sank a lot of time into reviewing the report and have other things to do so there is a risk of over-asking and them not wanting to engage any more. 


The reviewers for each section were as follows. Josh Horton reviewed a section on solar geoengineering which I am still in the process of revising for a later version. 

Peter Watson, Goodwin and James Ozden provided comments on various  sections in the report. 

Without wanting to pre-empt the reviewer comments if I am allowed to provide them, there was agreement with what I had written and I accepted the vast majority of proposed revisions. I think the main disagreement was that Keith Wiebe disagreed with some of my claims about extreme warming and agriculture. I think maybe Danny Bressler moderately disagreed with my assessment of Burke et al (2015), but not completely sure.  

Hi John Thanks so much for this. Did any of the reviewers (Peter Watson, Goodwin Gibbins, James Ozden perhaps?) make comments on the overall report ie your methodology, your choices of areas of inquiry etc. As this is my major criticism of your work I would really love to see the reviewers comments on your overall methodology, structure of the report etc Best Gideon

No I didn't get any of that. I don't want to put words in their mouths, but Peter overall seemed very positive. I'm less sure what Goodwin and James thought, but they didn't say anything massively negative, though perhaps they thought it

"I don't want to put words in their mouths, but Peter overall seemed very positive"

As Peter, just in case this should come back to bite me if misinterpreted, I just thought I'd say I could give an informed review of certain physical climate science aspects and the report seems to capture those well. I am positive about the rest as being an interesting and in depth piece of scholarship into interesting questions, but I can't vouch for it as an expert :-)

Would you suggest the depth of your feedback was the depth of peer review? And I'm correct in saying therefore that you didn't really review the overall methodology used etc?

I'd say the depth of review was similar to peer review yes, though it is true to say that publication was not conditional on the peer reviewers okaying what I had written. As mentioned, the methodology was reviewed, yes. So, this is my view, having taken on significant expert input. 

A natural question is whether my report should be given less weight eg than a peer reviewed paper in a prominent journal. I think as a rule, a good approach is to try start by getting a sense of what the weight of the literature says, and then exploring the substantive arguments made. For the usual reasons, we should expect any randomly selected paper to be false. Papers that make claims far outside the consensus position that get published in prominent journals are especially likely to be false. There is also scope for certain groups of scientists to review one another's papers such that bad literatures can snowball. 

This isn't to say that any random person writing about climate change will be better than a random peer reviewed paper. But I think there are reasons to put more weight on the views of someone who has good epistemics (not saying this is true of me, but one might think it is true ... (read more)

Peer review is very variable so it's hard to say what "the depth of peer review" is. I checked the bits I was asked to check in a similar way as I would a journal article. No I didn't myself really review the methodology. The process was also quite different from normal review in involving quite a few back-and-forth discussions - I felt more like I was helping make the work better rather than simply commenting on its quality. It also differed in that the decision about "publishing" was taken by John rather than a separate editor (as far as I know). 

I would say that for all of the 'non-EA' reviewers, the review was very extensive, and this was also true of some of the EA reviewers (because they were more pushed for time). The non-EA expert reviewers were also compensated for their review in order to incentivise them to review in depth. 

It is true that I ultimately decided whether or not to publish, so this makes it different to peer review. Someone mentioned to me that some people mean by 'peer review' that the reviewers have to agree for publication to be ok, but this wasn't the case for this report. Though it was reviewed  experts, ultimately I decided whether or not to publish in its final state. 

Hi John, Thanks for this openness, its really appreciated. Any update as to whether the reviewers are happy for their comments to be share? Best Gideon
So you didn't get anyone reviewing your overall approach or methodology? Don't you perhaps think this is a bit of an oversight given how influential this report is likely to be?

Oh sorry, I thought you meant 'did they leave negative comments about these things'. Lots of people looked at the overall report and were free to point out things I missed.

I still don't really understand why you have such an issue with the methodology. I took my methodology to be - pick out all of the things in the climate literature that are relevant to the longtermist import of climate change, review the scientific literature on those things, and then arrive at my own view, send it to reviewers, make some revisions, iterate. 


I have an issue with Takakura and other models. All models I've seen measure climate impacts in a) a social cost of carbon, whose value is based on a pure time preference discount factor, or b) impacts by the end of the 21st century, which ignores impacts into future centuries. Both of these methods are incompatible with a longtermist ethical view.

If we wanted to get a longtermist-compatible estimate of climate damages, we would have to either calculate a social cost of carbon with a zero discount factor (except for growth-adjustments), or calculate total climate damages over hundreds of years. None of the studies I've seen do this. Even worse, we know that climate models are highly sensitive to the choice of discount factor, which is only possible if a large proportion of damages occur in the future, so we could be underestimating this future damage by a lot. How do you deal with this issue when studying climate change from a longtermist perspective?


Hi Karthik thanks for this comment. 

On your first comment, the Takakura et al (2019) study I mention and other models estimate a climate damage function, which is independent of a discounting module. The social cost of carbon is a function of a socioeconomic module, a climate module, a damages module and a discounting module as shown in the schematic below

Source: Resources for the Future, The Social Cost of Carbon: Advances in Long-TermProbabilistic Projections of Population, GDP, Emissions, and Discount Rates, October 2021

It is true that some models discount future costs in part with pure time preference. But I am here talking about the damage module which is the undiscounted aggregate damages, not the social cost of carbon. 

Also, it is not true that all studies have a positive rate of pure time preference. The Stern review is one prominent counterexample, for instance. 

I agree that some (though not all) models typically only consider impacts up to 2100. However, impacts up to 2100 are long-term relevant. If climate-economy models suggested that climate change would cause extinction or civilisational collapse or stagnation before 2100 (as some people seem to t... (read more)

If you think we are in the hingiest or most important century, then the impacts of climate change this century are in fact the main thing that determine its long-term effects

This is untrue if the things that make this century hingey are orthogonal to climate change. If this century is particularly hingey only because of AI development and the risk of engineered pandemics, and climate change will not affect either of those things, then the impacts of climate change this century are not especially important relative to future centuries, even if this century is important relative to future centuries.

All the indirect effects of climate that you consider are great-power conflict, resource conflict, etc. I have not seen arguments that claim this century is especially hingey for any of those factors. Indeed, resource conflict and great power conflict are the norm throughout history. So it seems that the indirect effects of climate on these risk factors is not only relevant for the 21st century but all centuries afterwards.

Takakura does not have a discounting module but considering impacts only up to 2100 is functionally the same as discounting all impacts after 2100. Obviously impacts ... (read more)


This is untrue if the things that make this century hingey are orthogonal to climate change. 

I do not think this is true. If we are at a hingey time due to AI and bio, and climate does not affect the hingeyness of this century, then it does not have much impact on the long-term. 

Takakura does not have a discounting module but considering impacts only up to 2100 is functionally the same as discounting all impacts after 2100.

You initially said that Takakura et al has a discounting module because it endorses pure time preference. I pointed out that this is not true. So, this seems like changing the subject

Karthik Tadepalli
I did not say Takakura has a discounting module and this is not changing the subject. What I said was: Takakura has the latter problem, which is my issue with it as you use it. This doesn't seem right as a criterion and is also counter to some examples of longtermist success. For example, the campaign to reduce slavery improved the long term by eliminating a factor that would have caused recurring damage over the long term. Climate mitigation reduces a recurring damage over the long term: if that recurring damage each year is large enough, it can be an important longtermist area. My point is that the impacts of climate in the 21st century are probably a substantial underestimate of their total long-term impact. It's totally possible that when you account for the total impact it is still not important, but that doesn't follow automatically from climates effect on hingeyness.
Fair enough on your Takakura point, I misread.  I'm not sure I understand your second comment. 'hingey' means that we are living at the most influential time ever. This includes things like value change around slavery. 
My thought here would be that if climate effects (or other factors) don't substantially reduce the rate of technological and economic progress over the 21st century, then effects after the 21st century might be likely to be pretty small  because our capacity to mitigate them would be enormous. If world real GDP keeps growing at a 3% annual rate, then GDP would be at about a quadrillion dollars/year in 2100 if I'm doing my math right (of course, one might argue it's likely to be much higher due to AGI, much lower due to slowing technological progress etc.). But that kind of enormous world output would make solutions like scaling up direct air capture to get massively negative carbon emissions feasible. In light of that, it makes a lot more sense to worry about how climate change impacts humanity's trajectory over the next 80 years than it does to worry about what the impacts will be after 2100. 
Karthik Tadepalli
Climate-economy models factor in technological and economic progress, and yet their SCC estimates are hugely sensitive to the discount rate. The only way I can see this happening is if climate damages in the future are very large.
That assumes a relatively happy path. If there's some other major one-off catastrophe (eg a major pandemic), the long-term effects of climate change will end up being far harder to deal with.

Can you make your model of indirect risks accessable to the public? Its asking for access. Thanks a lot. 

Also, why do you assume that "most of the risk of existential catastrophe stems from AI, biorisk and currently unforeseen technological risks."? My impression from earlier in the chapter is that you are essentially drawing the idea you can essentially ignore other potential causes from the Precipice. Is this correct? 

Moreover, this assumption only seems true if you assume an X-Risk will come as a single hazard. If it is, say, a cascading risk, cascading to civilisational collapse then extinction, then the idea these are the biggest risks should be questioned. Simultanously, if you view it as a multi-pulsed thing, say civilisational collapse from one hazard or a series of hazards or cascades, and then followed by whatever may (slowly) make us extinct- once civilisation is collapsed its easier for smaller hazards to kill us all, then once again the primacy of these hazards reduces. Only if you take a reductive view that sees extinction as primarily due to direct, single or near single, hazards that kill everyone or basically everyone, can this model be valid. 

Of cou... (read more)


The model should be shared now. 

Yes that is correct re my assessment of the other existential risks. I'm taking a view similar to Toby Ord and I suppose the rest of the EA community about where the main risks are. Of course, my main goal in the report is not to make this substantive case; I largely take it as given. 

I don't really see how viewing climate change as a cascading risk would change the overall risk assessment. If you argue that climate change is a large cascading risk then you would have to think that climate would play an important role in starting the cascade from collapse to extinction. I don't see how it could do that and explain why at length in the report. Can you lay out a concrete scenario that sketches this cascading risk worry that isn't already discussed in the report?

The report does suggest that climate change would make civilisational recovery harder but for plausible levels of warming, it would not be a large barrier to recovery and this should be clear from the substantive discussion in the report

Moreover, you suggest that "there is some chance of civilisational collapse due to nuclear war or engineered pandemics," essentially suggesting other c

... (read more)
Hi John, "I don't really see how viewing climate change as a cascading risk would change the overall risk assessment. If you argue that climate change is a large cascading risk then you would have to think that climate would play an important role in starting the cascade from collapse to extinction. I don't see how it could do that and explain why at length in the report. Can you lay out a concrete scenario that sketches this cascading risk worry that isn't already discussed in the report?" Having read the report, I am still unclear where in the report you lay out this substantive case. Could you please point this out to me, and I will be happy to reread it as I must have missed it. Also note I don't just refer to cascading risks, but to systemic risks, existential vulnerabilities and exposures etc. Please show me where in your report you make a substantive case against these ideas as well. Thanks! Moreover, cascading risks may only be to civilisational collapse, and may not even get you to extinction. If, as you suggest, climate change makes recovery harder, this may be a major problem from an X-Risk perspective. I agree, its unlikely a cascade would directly lead to extinction, but if it leads to major societal collapse (which your piece also doesn't seem to define), and recovery is harder, this may be enough to pose an X-Risk.  "The report does suggest that climate change would make civilisational recovery harder but for plausible levels of warming, it would not be a large barrier to recovery and this should be clear from the substantive discussion in the report" The report suggests this but doesn't, as far as I can tell from having read the report, make this case particularly substantively. Also, in the section where this seems to be discussed most at length "subsequent collapse", there doesn't seem to be any citations  If you could point me to what sources you have used to show that it shouldn't pose a large barrier to recovery, this would be nice. You sug

I think it might help to make this discussion more concrete if you gave an example of what you mean by a cascading risk. It's hard to defend the arguments in the report when I'm not sure what you are saying I have missed in my analysis. I talk about risks to the food system, and the spillover effects that might come from that (eg conflict), I talk about purported effects on crime, I talk about drought, I talk about tipping points etc. What is the casual story you have in mind?

The substantive discussion is the outline all of the various impacts that I have discussed and summarising the literature on economic costs, which tends to find costs of 4ºC are on the order of 5% of GDP. Unless something is radically missing from these analyses, I'm not sure how climate change could make a large difference to the chance of recovery from collapse. 

How about a scenario where a multitude of factors eg climate related damages, civil conflict, interstate conflict, bioweaponary, natural disasters and economic collapse all work in concert with each other? 

I discuss the potential impacts of climate damages, civil conflict, interstate conflict and the economic impact of climate change at con... (read more)

Hi John,

So sorry for the lateness of this reply, I have been super busy, and this reply will also only be short as I ma very busy. It would be good to organise a meeting to chat about this at some point if your interested.

On cascading risks, I tink a good recent discussion of cascading risk is found in https://www.nature.com/articles/s41467-021-25021-8 .  A plausible causal story for how climate change leads to a cascade may be as follows. This is obviously flawed and incomplete and clearly needs more study:

  • To respond to growing threats from climate change, adaptation measures (often technological) will be put in place. However, these adaptation measures, such as physical defences, are often very fragile. Whilst it is possible agricultural production increases, this would also likely be due to adaptation measures, with new things introduced likely to be less resilient due to lack of experience. Moreover, as certain regions get agriculture more badly hit, it is possible you see a few increasing agricultural hubs as those places less effected by climate change/could adapt quicker. This further increases vulnerability
  • One or a number of critical nodes in this system are hit by a h
... (read more)
Corentin Biteau
Thanks for the comment, it was interesting to have examples. By chance, do you have some documentation on cascading risks caused by shortfalls on energy production? Or more data on what would cause the economy to collapse? I'm looking for this since I have made some posts on energy depletion and trying to keep updating.   By the way, I find the lack of answer by John rather worrying, especially as this seems to be a crucial point you're making, especially in our interconnected world. Did you manage to chat with him?

Imagine that only a few hundred people in the world thought that climate change is an important problem (rather than at least tens of millions), that philanthropists worldwide spent a few million dollars a year on climate (rather than $10 billion), that society as a whole spent a million dollars on the problem (rather than $1 trillion), and that the international institutions trying to tackle the problem either don’t exist or have a similar budget to a McDonald’s restaurant. How bad would climate change be? This is how bad things are for the other global catastrophic risks, and then some.

Great analogy!

Thank you for writing this - looking forward to diving into the full report this weekend. Congratulations on finishing what must have been a major undertaking! 

Hi John,

The executive summary is below and the full report is here

It looks like the link is broken:

"AI: Forecasters on the community forecasting platform Metaculus think that artificial intelligent systems that are better than humans at all relevant tasks will be created in 2042."

How do you get this from the questions' operationalization? 

I thought that was what was meant by AGI? I agree that the operationalisation doesn't state that explicitly, but I thought it was implied. Do you think I should change in the report?

I think this strongly depends on how much weight you expect forcasters on metaculus to put onto the actual operationalization rather than the question's "vibe". I personally expect quite a bit of weight on the exact operationalization, so I am generally not very happy with how people have been talking about this specific forecast (the term "AGI" often seems to invoke associations that are not backed by the forecast's operationalization), and would prefer a more nuanced statement in the report.

 (Note, that you might believe that the gap between the resolution criteria of the question and more colloqiual interpretations of "AGI" is very small, but this would seem to require an additional argument on top of the metaculus forecast). 


Hi John,

I would appreciate your thoughts on the shape of the relationship between existential risk due to climate change and global warming. For example, would it be reasonable to assume it is linear, i.e. that the x-risk linked to an increase of 2 ºC relative to today's temperature is 2 times as large as the x-risk linked to an increase of 1 ºC?


I have different understanding of moisture greenhouse based on what I've read. You said (oversimplifing) that the threshold for moisture greenhouse is 67C  and the main risk  from it is ocean evaporation.

But in my understanding 67 C is the level of moisture greenhouse climate. The climate according to some models will be stable on this level.  67 C mean temperature seems to almost lethal to humans but some people could survive on high mountains. 

However, the threshold to moisture greenhouse, that is the tipping point after which the ... (read more)

Thanks for this. Someone else raised some issues with the moist greenhouse bit, and I need to revise. I still think the Ord estimate is too high, but I think the discussion in the report could be crisper. I'll revert back once I've made changes
I am going to have a post about the risks of runaway global warming soon.
1[comment deleted]
here https://forum.effectivealtruism.org/posts/bdSpaB9xj67FPiewN/a-pin-and-a-balloon-anthropic-fragility-increases-chances-of

Is there much/any concern here that global warming could increase the risk of a far more deadly pandemic stemming from natural sources? 

Where I am located, as the coolest months warm known viruses in animals are occurring in these cooler months for the first time. Anecdotally, on top of becoming more frequent they also appear to be increasing in severity. 

Further, could this increased pandemic risk due to global warming (if true)  help bring attention and resources to biosecurity in general which could also help prevent engineered viruses?


... (read more)

Action on climate change is in its infancy and forecasts cannot be relied as they cannot include unforeseen events.  Given human nature ie people do what is the least inconvenient to them (ie act in their own self interest) rather than what is morally right, I'm expecting a backlash to CO2 reducing policies which I doubt the IPCC forecasts include. Will the majority of people pay for new green infrastructure and a more expensive hydrogen economy?  People are already up in arms about the current energy cost rises. Will Governments stand up to the ... (read more)

From a longtermist point of view, it is especially important to avoid outcomes that could have persistent and significant effects. These include events like human extinction, societal collapse, a permanent negative change in human values, or prolonged economic stagnation.


Over the long term, it seems reasonable to think in terms of cycles.   You know, the pattern over the long term is that civilizations live, and then they fall, and then something else rises to take their place.  

The Roman Empire must have seemed permanent to those living at... (read more)

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