I think it is a very hard area to provide an accurate outline of, and I think to do that you need to go beyond reading the abstracts of papers and to look at the assumptions in those paper which typically combine very pessimistic warming, very pessimistic economic growth, limited or no adaptation. I think a lot of your analysis errs in a pessimistic direction. 

1. [edit: misread the first point]: "The IPCC’s 6th Assessment Report predicts that, even if we fail to undertake significant further action, it’s very unlikely that we’ll reach 3°C or more of warming." I'm not sure where you are getting this from given that you direct the reader to a >3000 page report, but this is now widely accepted to not be true. As I discussed in my report on climate change, warming of 2.5C is widely accepted to be the most likely outcome on current policy by a range of modelling studies. Since this does not account for changes in policy, this is pessimistic. 
2. It is notable that you ignore climate economics in your overview. This is the field tasked with estimating the aggregate costs of climate change, and most models find that the costs of warming for 2-3C are a 0-5% reduction of GDP relative to a world without warming. Since GDP per capita will increase several fold up to 2100, average living standards will still be higher. These models do not find that the costs of 1.5C would be 'huge', rather that they are close to a 0% reduction in GDP. Given that we are already pretty close to 1.5C, it is pretty obvious that the effects will not be 'huge' (but I'm not sure what you mean by that). 
   1. Do you disagree with these models? If so, why? The best ones include the impacts you talk about here, including food, flooding drought, heat stress etc, and find the same results. I don't think you should be selective in accepting the expert consensus on things without evidence or argument. 
   2. You say that climate change will increase food insecurity. True, but studies that incorporate the effects of climate change, economic growth and agricultural progress find reductions in food insecurity on nearly all socioeconomic scenarios. I think it would be worth providing this context. 
3. Drought 
   1. You cite the carbonbrief article on people subject to drought which, for those who can be bothered to check, cites this article, which does not consider adaptation in its estimates and so is not realistic. 
   2. You cite the study saying that 132 million extra people will be exposed to drought in a 1.5C world. We are already nearly in that world and this decade a total of 662 people have died from drought per year, according to Our World in Data. This would be useful context. 
   3. Water scarcity is mainly driven by mispricing of water and especially subsidies of water for farmers. 
4. Temperature-related deaths
   1. You say that at 1.5C "nearly 14% of the world’s population could experience severe heatwaves at least every five years". Yes, but we are nearly in that world today, and today cold-related deaths are 9x heat-related deaths (Zhao et al 2019). In the near-term at least we should expect temperature-related deaths to decline due to climate change. I think you should at least note this in your overview. 
   2. You cite Bressler et al (2023). Bressler et al claim that assuming limited adaptation, very pessimistic economic growth (SSP3) and very pessimistic warming (RCP8.5), deaths increase by 5 million per year by 2100. Per the IPCC, it is not actually permitted to combine SSP3 and RCP8.5, but studies often do this. Bressler et al also doesn't consider many important forms of adaptation, which have led to declining heat-related deaths in rich countries. Consequently, I think the estimates in Bressler et al are not accurate, at least biased high by several orders of magnitude and probably have the wrong sign. 
5. Tipping points 
   1. You note the release of vast amounts of methane from the Arctic. There is one study asserting without evidence that this would happen, but it is extremely controversial and expert elicitation suggests that methane clathrates would increase 2100 temperatures by at most 0.1C on an insanely pessimistic emissions scenario (RCP8.5). 
   2. You cite the Kemp et al study claiming "sudden, severe, and potentially irreversible changes to the climate" but they don't provide any evidence for this and the IPCC denies this, if you mean "an shift in global climate that happens due to warming before 4C that adds more than 2C to global temperatures". The main argument provided in the Kemp paper is a causal loop diagram with a lot of arrows running between climate change and other problems. It is notable that one could apply the same analysis to other things such as 'bad economic policy' without arriving at the conclusion that this is a serious catastrophic risk. 
   3. In general, if you are defining 'catastrophic risk' in the usual way, could you explain how you get to >800 million deaths from climate change via a non-conflict pathway? The biggest death estimate for a particular impact I have seen is the Bressler et al claim that assuming limited adaptation, very pessimistic economic growth (SSP3) and very pessimistic warming (RCP8.5), deaths increase by 5 million per year by 2100. (Per the IPCC, it is not actually permitted to combine SSP3 and RCP8.5, but studies often do this.) On more plausible assumptions, I would expect temperature-related deaths to decline. Even if you take the Bressler estimate at face value, where do you get the remaining >795 million deaths? For all other impact pathways I have seen, deaths from weather-related events are set to decline relative to today due to economic growth and adaptation. 
6. Conflict 
   1. In support of the claim that climate change is an important contributor to conflict risk you cite an 80,000 Hours article. The IPCC is highly equivocal on the effects of climate change on civil conflict. It basically says nothing about the effects on interstate conflict and no scholars of great power war think it is an important driver of 21st century potential great power conflicts. 

Thanks a lot for the response! I was the main researcher for these articles - here are a few thoughts from me and the team:

It’s a little tricky for us to evaluate the consensus on these issues ourselves as we don’t have the capacity or expertise to review all the relevant papers and assess their relative influence. (We’d welcome anyone sharing their views on this, especially if they have expertise in the field!)

Because of this, we typically defer to respected authorities – especially the IPCC – which is likely a decent proxy for expert consensus. While any one institution will inevitably have its shortcomings, the IPCC's comprehensiveness in reviewing the literature is impressive, and they do a fairly good job of representing their uncertainty based on the literature in their reports.

That being said, there seems to be a lot of uncertainty about expected adaptation efforts, perhaps more so than there is uncertainty about the direct effects of climate change, and the extent to which the IPCC provides estimates accounting for adaptation depends on the problem. In short – we don’t really know, (though we’re open to being corrected on this). 

Because of this, when trying to estimate the value of working on adaptation, given high uncertainty about how much of it will take place without our intervention, as well as a reportedly widening adaptation finance gap, it’s still worth thinking about the expected impacts assuming minimal or current-trajectory adaptation. Though, naturally, the more we learn about the impact of expected adaptation efforts, the better.

Here’s a few more specific points on deaths from non-optimal temperatures and natural disasters:

On temperature and mortality:

When discussing the promisingness of an adaptation response to heat stress, we think what matters is the absolute numbers of heat-stress-related deaths, which we can be quite confident will significantly increase, and not whether on net climate will cause or prevent more deaths (taking into account other types of deaths prevented). We included the estimate that increases in fatalities will outweigh reduction in deaths because it provides interesting and relevant context, not because it directly bears on how promising this area of adaptation is.

It’s also worth noting that even Zhao (2021) claims that ‘in the long run, climate change is expected to increase the [temperature-related] mortality burden’, even if it reduces mortality in the short term. They don’t give any concrete projections, so it’s unclear the extent to which the numbers we’ve given align with this claim – but the direction is the same. Nonetheless, this does complicate the discussion around temperature-related mortality, so thanks for bringing it to our attention!

On natural disasters:

First, although fatalities from natural disasters have decreased, most of this reduction has been in high-income countries (if you look at the OWID page and filter by low-income countries, the downward trend is much less clear). 

Additionally, looking at the decadal average of all natural disasters can hide how sparse the data points driving this impression are. If we look at the year-by-year view of natural disaster deaths, just a handful of terrible events are responsible for the vast majority of deaths throughout the 20th century, which means we’re wary about inferring long-term trends from the decadal view – especially for events that fit a power-law distribution.

On top of this, looking at the specific kinds of natural disasters we’re discussing, it’s not clear they’re subject to the same downward trend, even on the decadal view. For instance, the OWID chart on natural disasters shows deaths from extreme temperatures have sharply increased in recent decades, and annual flood deaths have been fairly flat since the 1970s.

And just as a general point on the importance of climate-related extreme weather events, only counting fatalities may also give us a misleading picture, since it excludes other significant effects like damage to infrastructure, worsened mental health, and cumulatively huge economic losses. Again referring to the OWID page, the economic damage inflicted by natural disasters is much higher now than it was in the 1960s (as a share of GDP), despite them causing fewer deaths.

Our current view is that looking at the century-long average as an estimate of expected future fatalities may be an overestimate (primarily due to reductions in high-income countries), but it’s unclear that existing adaptation efforts will similarly continue to reduce harms going forward (or prevent potential rises in disasters where such are expected due to climate change).

The bottom line is we think there’s a lot of complexities in the analysis of the quantitative estimates, especially when adaptation and human response is a critical factor. But we believe that the areas we’ve identified are nonetheless promising areas to have a positive impact given what we know.