Also posted on my blog.

In the The Wizard and the Prophet, Charles Mann gives a great summary of the issues that come up when thinking about longterm problems.

The passage is about climate change but it applies just as well to other longterm stuff:


In the spring of 2016, my friend Rob DeConto published an article in the scientific journal Nature. By chance, our families had dinner together a day after its release. Rob was both cheerful, because he had just finished a long project, and uneasy, because of the implications of that project. With a colleague, David Pollard, he had spent years examining the Antarctic sheet, by far the world’s largest ice mass. Past researchers had thought that because of its size it would respond slowly to rising global temperatures. To their dismay, DeConto and Pollard had realized that Antarctica might be more vulnerable than previously thought.
Increasing temperatures would attack the ice in two ways: warmer air would melt it from above, forming pools on the surface, and warming ocean currents would eat at the underside of the sheet, creating large cracks. The pools on the surface could drain through the cracks, widening them and splitting the ice sheet into unstable pieces that would fall apart under their own weight. The remaining chunks, surrounded by warm water and air, would melt quickly, like the ice cubes in a cocktail. If the two men were correct, melting Antarctic ice could by itself raise the world’s oceans more than three feet by 2100, enough to swamp Miami, Tokyo, Mumbai, New Orleans, and many other cities. By 2500 the rise could be as much as fifty feet.
Every few years the Intergovernmental Panel on Climate Change (IPCC), a United Nations-sponsored international scientific consortium, issues a set of lengthy, multivolume reports that attempt to portray the state of the science on climate change. In 2013 it put together a consensus projection of how sea level would be affected by a variety of factors, including the melting of glaciers in Greenland, the shrinking of the Arctic ice cap, and the fact that water expands as it gets warmer (the increase is slight, but it adds up when extended across the whole globe). Taken together, the IPCC estimated, these would push up the sea roughly twenty-eight inches by 2100. Antarctica, the biggest ice mass, would remain more or less intact, contributing only one to three inches to the total. This idea seemed borne out by the facts – in the previous few decades, Antarctica had shown little sign of melting. Indeed, parts of the ice sheet were growing.
But the IPCC also thought that scientists needed to look more closely, just to be sure. Now DeConto and Pollard had performed that analysis, and they were saying that there was a chance that Antarctica could fall apart by 2100, and that therefore the seas could rise higher and faster than the IPCC had imagined possible. “For a geophysicist, what’s going on is stunning,” my friend told me. “We used to believe these systems needed thousands of years to make these shifts. Instead it’s happening so fast that it’s terrifying. Conceivably, you could start seeing truly bad effects in a hundred years.”
And this is one of the great difficulties in thinking about climate change: what seems terrifyingly fast on the geological scale is unfathomably long on the human scale.
By “truly bad effects” DeConto meant flooded coasts, vanished islands, awful droughts, and, maybe, storms of unprecedented power. But even if these occur in the time he fears – even if they transpire in the geologically insignificant span of a century – they will not be seen by him or me. Quite possibly every person who reads this book will be dead before they occur, as will most of their children. How many governments make plans for such long-term contingencies? How many families do?
The most likely victims of climate change, in the short run, are people who live on oceanic islands, in very low-lying coastal settlements, in ice-bound Arctic communities, and around forests that burn after unwonted dry spells. Millions of people live in these places, but they are a small fraction of the world’s billions. The greatest potential harms of climate change will be experienced by future generations – centuries in the future, or even millennia. By our actions today (burning fossil fuels), the argument is, we are dumping problems (drought, sea-level rise) on tomorrow.
On the one hand, forcing other people to clean up our mess violates basic notions of fairness. On the other hand, actually preventing climate-change problems would require societies today to make investments, some of them costly, to benefit people in the faraway future. It’s like asking teenagers to save for their grandchildren’s retirement. Or, maybe, for somebody else’s grandchildren. Not many would do it.
Would they be wrong? How much concern should we have for future generations? The harder one looks at the problem, the more confusing it seems. “The problems of climate change,” says the New York University philosopher Dale Jamieson, “swamp the machinery of morality.” (“A perfect moral storm,” says Stephen M. Gardiner, another philosopher.)
The basis for arguing for action on climate change is the belief that we have a moral responsibility to people in the future. But this is asking one group of people to make wrenching changes to help a completely different set of people to whom they have no tangible connection. Indeed, this other set of people doesn’t exist. When one tries to make plans for nonexistent people, the result is an intellectual quagmire, because there is no way to know what those hypothetical future people will want.
Today we live in a world where almost everywhere slavery is illegal, women can vote and own property, and overt obeisance to social class is frowned upon. Most decision-makers who lived three hundred years ago would have regarded these developments with horror. Had they grasped that the future could be like this, they would have sought to prevent it.
Picture Manhattan Island in the seventeenth century. Suppose its original inhabitants, the Lenape, could determine its fate, in perfect awareness of future outcomes. In this fanciful situation, the Lenape know that Manhattan could end up hosting some of the world’s great storehouses of culture – the Metropolitan Museum of Art, the American Museum of Natural History, the Museum of Modern Art, the New York Public Library, the opera and symphony at Lincoln Center.
All will give pleasure and instruction to countless people. But the Lenape also know that creating this cultural mecca will involve destroying a diverse and fecund ecosystem. I suspect the Lenape would have kept their rich, beautiful homeland. If so, would they have wronged the present?
Economists tend to scoff at these conundrums. Forget all of this philosophical foofaraw about the rights of hypothetical people, they say. That’s just a smokescreen for “paternalistic” intellectuals and social engineers “imposing their own value judgments on the rest of the world.” (I am quoting the Harvard economist Martin Weitzman.)
Instead, economists suggest, one should observe what people actually do – and respect that. In their daily lives people care most about the next few years and don’t take the distant future into much consideration – they prefer “present over future utility,” in the economist’s phrase.
In technical terms, this idea is expressed with the discount rate, which is like the antimatter version of an interest rate. Imagine that today I would pay $200,000 for a new house. How much would I pay today if I had to wait five years to receive the house? $100,000? $50,000? Today and tomorrow, the house is the same physical object. But as a rule people won’t pay as much for a house they have to wait for as a house they can occupy immediately, and the longer they have to wait, the less they are willing to pay. Usually economists use 5 percent as a discount rate – for every year of waiting, the price goes down 5 percent, compounded. Doing the arithmetic, a 5 percent discount rate means that goods and services are worth roughly half as much to me in fifteen years as they are today.
The implications for climate change are both striking and, to many people, absurd. At a 5 percent discount rate, the Argentine-American economist Graciela Chichilnisky has calculated, “the present value of the earth’s aggregate output discounted 200 years from now is a few hundred thousand dollars.” In econospeak, “the earth’s aggregate output” means “the human race and all its works.” To prevent our species from being wiped out in two centuries, Chichilnisky points out, standard economics suggests that the world would pay “no more than one is willing to invest in an apartment.”
Intuitively, I am hard-pressed to believe that most people would endorse the notion that the future of humankind is worth no more than a single apartment. Chichilnisky, a major figure in the IPCC, has argued that this kind of thinking about discount rates is not only ridiculous but immoral; it exalts a “dictatorship of the present” over the future. Economists could retort that people say they value the future, but don’t act like it, even when the future is their own. And it is demonstrably true that many – perhaps most – men and women don’t set aside for retirement, buy enough insurance, prepare their wills, or a hundred other precautions, even if they have sufficient resources. If people won’t make long-term provisions for their own lives, why should we expect people to bother about climate change for strangers many decades from now?
Not so fast, says Samuel Scheffler, a New York University philosopher who is the author of Death and the Afterlife (2013). The way people feel and act about their individual futures is not the same as how they feel and act about our species’s collective future. In his book, Scheffler discusses another book: Children of Men, a best-selling 1992 science fiction novel by P. D. James that was adapted into a movie by the filmmaker Alfonso Cuarón. The premise of both book and film is that humanity has suddenly become infertile, and our species is stumbling toward extinction. In this scenario, as Scheffler notes, nobody alive is worse off, at least in the short run. Couples are denied future children, but they lose no children they already have; nobody even loses money. The present doesn’t change materially. All that is lost is a future that we would never have seen.
Both book and movie show this world as one of anomie and despair. Because our species has lost its future, life seems meaningless. Civilization wanes; aimless, violent gangs roam ruined streets. The belief that human life will continue, even if we ourselves die, is one of the underpinnings of society. Logically speaking, the desolation in Children of Men is peculiar. As Scheffler points out, all people have known from childhood that they will die. As individuals, we have no long-term future. Personal extinction is guaranteed. But this tragedy – one that will be directly experienced by every single man, woman, and child – provokes no public alarm. No tabloid has ever blared the headline, “All 7.3 Billion of Us to Vanish Within Decades.” Our conviction that life is worth living is “more threatened by the prospect of humanity’s disappearance than by the prospect of our own deaths,” Scheffler writes in Death and the Afterlife.
The idea is startling: the existence of hypothetical future generations matters more to people than their own continued existence – “evidence of hitherto unsuspected reserves of altruism,” as Scheffler drily comments.
What this suggests is that, contrary to economists, the discount rate accounts for only part of our relationship to the future. People are concerned about future generations. Even if the logic is hard to parse, they think that humanity’s fate is worth more than an apartment. But trying to transform this general wish into specific deeds and plans is confounding.
Imagine a ladder of moral concern that begins with an exclusive concern for oneself and extends through concern for family to concern for culture or religion to concern for all cultures and religions and beyond that to future generations. At the far end is the Margulis position, a concern for a natural order that is so all-encompassing that it is hard to distinguish from unconcern.
It is a philosophical truism that exclusively caring about oneself is not a route to a happy or satisfying life. Another philosophical truism is that a lofty concern for all of existence is the province of saints, and sainthood is not required for ordinary people to live decently and well.
In the middle, where most people spend their days, it is hard to distinguish morally between positions. It is easy to disparage people who think only of their family or neighborhood. But higher up the ladder is not necessarily better – think of the numberless instances where people, genuinely believing that they are acting for the benefit of larger entities, have ended up doing awful things. Would the world have been better off if the soldiers in the Crusades had not tried to spread the light of Christianity and instead had stayed home and improved their own villages? Or, again, consider Manhattan Island. If the level of concern is for preserving all cultures, it might make sense to bulldoze all the buildings and return the land to the Lenape. After all, there are many wonderful centers of Western culture; there is only one Lenape homeland. But removing the millions who live in Manhattan could not be done without creating terrible hardship and dislocation on the level of the community, quarter, family, and individual.
In addition, reaching for higher levels on the ladder of concern is more complex and difficult. If nothing else, the many misadventures of foreign aid have shown how difficult it is for even the best-intentioned people from one culture to know how to help other cultures. Now add in all the conundrums of working to benefit people in the future, so inherently unknowable, and the hurdles grow higher. Thinking of all the necessary actions across the world, decade upon decade – it freezes thought.
All of which indicates that although people are motivated to reach for the upper rungs, they are more likely to succeed in their aspirations if they stay rooted to the lower, more local ones.
Margulis, I suspect, would have put this in biological terms. Evolution has provided the human brain with marvelous tools for detecting and resolving fast-moving, clearly visible, small-scale, near-future risks. By the same token, the brain is easily overwhelmed by slow, abstract, large, long-term problems. Patiently dribbling money, year by year, into a retirement account, calculating the insurance needed to compensate for an unlikely but real hazard, contemplating the arrangement of one’s death – they boggle the mind. (Most people’s minds, anyway.) Climate change is all of these and more: gradual, impalpable, world-altering, multigenerational, a situation that will not become readily tangible until irreversible lines already have been crossed. “It is not the sort of problem that Mother Nature raised us to solve or even notice,” Jamieson, the philosopher, has written.

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At a 5 percent discount rate, the Argentine-American economist Graciela Chichilnisky has calculated, “the present value of the earth’s aggregate output discounted 200 years from now is a few hundred thousand dollars.”

  • 2019 Global GDP = around $88 trillion
  • Annual Real Growth Rate = assume 2.5%
  • Graciela's discount rate = 5%
  • Present Value of 2219 GDP = (88*10**12)*((1.025)**200)/((1.05)**200) = $710,224,969,039 (over $700 billion)
  • Present Value of 2219 and thereafter: ((88*10**12)/(0.05-0.025))*((1.025)**200)/((1.05)**200) = $28,408,998,761,567 (over $28 trillion)

Huh yeah, weird. Here's the source (Chichilnisky 1996), quote is on p. 5

Strangely they don't actually lay out the "simple computation."

I thought maybe they were getting down to a few hundred thousand by not factoring in a growth rate, but that still leaves you at a little over $3 billion.

So I'm not sure what's going on. Maybe Chichilnisky 1996 started with a much lower global GDP estimate? It was done 23 years ago.

For her calculations to be correct, present world GDP, absent growth, would have to be USD . Back in 1996, when the paper was published, world GDP was over USD . Unclear what's going on here.

I think the broader point is still important though.

It is weird that discount rates imply that a civilization hundreds of years in the future that's not growing won't be worth much in present decision-making (even if that civilization is very large).

Just saw Robin Hanson's post (a) on this, also.

Inferential distances and thus discount rates are vastly different depending on which metaphors you use to think about the future.

Could you give a couple example metaphors to help build my intuition here?

Some examples:

thinking in terms of generational shifts

thinking in terms of a given outcome things are evolving towards

thinking in terms of specific scenarios

thinking in terms of cycles

any of these can be thought about on multiple temporal horizons and people will give different answers depending on their mental habits.