Climate change is likely to kill a lot of people.[1] It is unlikely to kill all people. Longtermists worry about human extinction, typically more than they do about anything else. Accordingly, some longtermists present risks of human extinction in contradistinction to the risks of climate change, sometimes arguing that even a small risk of extinction is worse than the near certainty of major climate change. The (longtermist) Future Fund’s areas of interest do not include climate change, and other EA funders have spent much less on climate change than on other causes. According to a new, book-length longtermist report, “the risk of human extinction from the direct effects of climate change now seems extremely small… other problems are more pressing than climate change.” 

Skeptics about longtermism have seized repeatedly on this relative dismissal of one of the signature challenges of our time. This blogpost argues that longtermists can and should take climate change very seriously, by putting more money and creative efforts into investigating and fighting it and some of its worst repercussions. The reason is multiple lock-in bad effects that climate change could have on (1) human survival under so-called runaway scenarios, (2) human survival under the likeliest climate change scenarios, and (3) human life-quality and longevity under the likeliest scenarios, a matter which, I shall argue, longtermists have more reason to heed than they currently recognize. Finally, the blogpost distinguishes between strong and weak forms of longtermist dismissal of climate change and explains what is wrong with both.

(1) Climate change and human survival under runaway scenarios

In runaway scenarios, a factor augmented by global warming increases that warming, which further augments that factor, which further increases warming, and so forth. For example, the atmosphere comes to contain enough greenhouse gas to block thermal radiation from leaving earth, preventing the planet from cooling; plants that might have taken carbon dioxide out of the atmosphere die of heat, then rot, in a vicious cycle that causes greater net emissions and more heat and plant death. The result: much faster and more extreme global warming than under other scenarios, a largely uninhabitable planet, and, very possibly (though not certainty), human extinction. 

Runaway scenarios are far less likely than the most expected scenarios. But their likelihood is not zero, or infinitesimal. Multiple respectable climate scientists have argued that their likelihood is high or, recently, that canonical documents’ silence about them reflects mainly these documents’ optimistic biases. The chance for runaway scenarios is probably smallish. But longtermists, in particular, take smallish chances of complete disasters very seriously, in virtue of the large number that results from multiplying a smallish fraction by an astronomical number. 

(2) Climate change and human survival under the likeliest scenarios

Even under the likeliest scenarios of climate change, there are grave “indirect” risks—risks that emanate from possible human reactions to climate change. Temperatures in New Delhi reached 49°C this summer. In parts of Rajasthan, they reached 51°C a few years ago. If lethal heat and wet-bulb temperatures recur and spread, as they are likely to do, populations will not stay around to die. Most everyone who can will probably migrate. Millions may also migrate in Pakistan when a third of the country is again flooded. Globally, climate change “could force 216 million people... to move within their countries by 2050.” The political instability from such migration could develop in many ways. In these nuclear-armed nations, it could be a pathway to existential risk. Attempted mass migration to nuclear-armed neighbors Pakistan or China is another possible scenario. And climate change also means that “the Indian subcontinent is expected to face a severe water shortage – spiking the risk of Indo-Pakistan downstream river politics escalating into a water war.” A nuclear exchange between any two among India, Pakistan, and China could beget a larger nuclear war, nuclear winter, and civilizational collapse or even extinction. 

It is true that related increases in net-movement across international borders are, globally, far less likely than related movement inside countries. But even internal migration could create political instability that leads to war; and related cross-border migration is likelier in nuclear-armed South Asia than elsewhere, partly because in tropical regions, escaping increased temperatures will tend to require long travel. More broadly, several nations that are already “fragile” and likely to experience extreme temperatures in coming decades are also nuclear-armed (or have the capacity to produce the worst bioweapons). And there are additional pathways for climate change to increase the risk of a nuclear war. Geopolitical developments could go in many different directions following climate change’s upheavals. So confidence that the radical and sometimes abrupt changes wrought by climate change are unlikely to result in catastrophic military developments seems misplaced. 

There is another reason why climate change risks human survival even under the likeliest scenarios. Climate change would interfere with our ability to address extinction risks. States burdened by climate change could not expend efforts on preventing other catastrophic risks, yet “state capacity is important… for coordinating policy for social benefit,” including the prevention of catastrophes. Nations incensed about climate injustices are even less likely to promote global efforts to prevent catastrophes. For example, “Helping to draft the Bioweapons Convention becomes far less tractable if nations are unwilling to cooperate” because of climate change. Pressing needs for development, another factor with which climate change will interfere, were probably the main obstacle to successful completion of negotiations on nuclear disarmament. Finally, thus far, “the absence of nuclear war was less due to a lack of potential causes, than [sic] the global political system’s ability to defuse them.” And climate change could easily undermine that stability. 

In rich countries as well, climate-related reduction in economic growth over the coming decades and centuries will not only suppress quality of life. It would also delay the development of technologies to counter extinction risks. So climate change worsens differential technological progress, an extinction risk.

All in all, indirect effects make major climate change an existential risk even outside runaway scenarios. 

(3) Climate change, life-quality, and longevity under the likeliest scenarios

Even short of extinguishing our species, climate change is highly likely to spread punishing temperatures, rising sea levels, familiar and new diseases, chronic killer storms, fires, and floods, and much else. Importantly, some torturous and lethal developments would “last a very long time.” For example, temperatures are expected to rise and remain high. Hurricanes, floods, and wildfires are expected to remain chronic. In fact, “Some of the ecological effects of climate change get worse over time”. The same could not be said about the direct harms from many of the worst viruses, for example; their morbidity and mortality would disappear in the generation after they cease to circulate.

When longtermists worry about lock-in of bad effects that fall short of extinguishing the species, usually their focus is bad political developments, like long-term dictatorships of by all-powerful humans or AI. There is also interest in long-term good effects, such as humans becoming more compassionate. A far likelier locked in bad effect is the possibility that life becomes worse because climate change impairs our natural habitat—as it already does. 

Something that affects the life-quality and longevity of many or of all future people clearly matters, for the usual longtermist reason. If many or all of the vast numbers of future people live worse lives than future people would have lived, that is very bad indeed, other things being equal. 

At some level, I wish to add, longtermists should treat that vast loss of utility as worse than the same vast total loss of utility from failure to make happy people—people who are never created because the species disappeared earlier. Put differently, when total utility remains constant, lives that are far worse than the lives that would exist otherwise are in some ways even more concerning, to everyone including longtermists, than lives that are far fewer than the lives that would exist otherwise. 

This may seem like a peculiar statement given that many longtermists are totalists who deny precisely that. For totalists, what matters is total utility, and it does not matter whether that number is driven by the average number of utils per person or by the number of persons. But, I wish to insist, even longtermist totalists should treat utility loss driven by the average number of utils per person as worse. They should do so for one of the reasons that leading longtermists give for longtermism. The reason is that when we are unsure of what fundamental course of action morally we should take, part of what ought to guide us are the moral theories that we reject yet have some credence in. 

In our context, even totalists should not have 100% credence in totalism. There is, after all, a respectable debate in population ethics. And much reasoning suggests that we have stronger reasons and stronger obligations to make people happy than we do to make happy people, even when total utility remains constant. Totalists’ rejecting that viewpoint does not mean that they place 0% credence in it. Nor should they.

From a certain respectable non-totalist viewpoint (sometimes inaccurately referred to as “person-affecting” although it need not assume that all reasons and obligations are toward particular persons or require impact on particular persons’ interests), making people happy matters more than making happy people. The chance that this respectable non-totalist viewpoint is accurate should, according to the typical longtermist approach to moral uncertainty, weigh in favor of making people happy. So when other things are equal, it can serve as a thumb on the scale in favor of policies that protect future life-quality and longevity, as compared to ones that create a greater number of happy people.

A pragmatic reason for longtermists to pay special attention to working on solutions that promise to make people happy in the long run is that such solutions are likely to have wider appeal to nonlongtermists. Most of the latter would on reflection dismiss the urgency of creating as many happy people as possible. A chance at broad coalitions is a pragmatic advantage of projects that increase present and future populations’ life-quality and longevity over ones that bring larger future populations into existence—when the numbers are otherwise equal.

A reservation. Some longtermists are optimistic that “Within 100,000 years, the Earth’s natural systems will have scrubbed our atmosphere clean of over 90 percent of the carbon we have released, leaving the climate mostly restored and rebalanced.” While many harms from old and new emissions may last, it is also true that at some point, we may colonize more habitable stars, or develop microchips that are happy even in our sizzling planet. But longtermists take very seriously dictatorships that would last only for very long periods and not forever; and none of these escape routes of the harms of environmental devastation is guaranteed.

In sum, lock-in effects that would make vast numbers of future persons’ lives more brutish and short ought to command a high longtermist priority. Indeed, compared to lock-in effects on future people’s prospects of coming into existence, when effects on total utility are similar, the former should command a higher priority. Many of the most likely effects of climate change may well be of the kind that commands special priority for these reasons. That gives longtermists further reason to take climate change very seriously. 

Strong vs. weak longtermist dismissal of climate change, and why either is wrong

The three types of potential lock-in effects that I described suffice to question what we may call strong longtermist dismissal of climate change, namely, the view that climate change is of no concern from a distinctively longtermist viewpoint (although climate change may remain a concern otherwise). What about the weaker view, that climate change is a major longtermist concern, just not one that should currently attract longtermist resources? 

The weak view could be motivated by the claim that other causes pose even greater longtermist concern, for their even greater chance of leading to extinction or civilizational collapse; or the claim that, unlike some other causes of longtermist concern, climate change is not a neglected problem, because many nonlongtermist funders and researchers are dedicated to fighting climate change. 

The weak view founders as well.  The admittedly greater extinction potential and scantier funding of some other existential risks as broad categories does not mean that the same applies to every subcategory of those risks and to every proposed response. Specific research and tools on climate change will complete well with specific research and tools from generally more-urgent cause areas. 

There is for example vast scope for cost-effective research on climate-change related pathways to x-risk scenarios and on “ranking various climate interventions from a climate x-risk perspective.” More thinking and action are also needed on nonstandard but potentially transformative solutions for climate change, of the type that longtermism’s and effective altruism’s creative heads are uniquely positioned to develop. Consider solutions that most progressives reject because of their serious downsides and risks: geoengineering, reliance on nuclear power for energy, and, more generally, harm-reduction responses to climate change and to its dangerous consequences. 

A general lesson is that in setting global priorities, some interventions from a lower-ranked cause area will beat some from a higher-ranked one. The former might have sufficient promise to be transformative or cheap as to beat interventions from higher bands. 

Conclusion

Longtermists should take climate change very seriously, and more seriously than they currently do, because of multiple potential lock-in bad effects of climate change. Climate change might extinguish the species either under runaway scenarios or under the likeliest scenarios. And under the likeliest scenarios, climate change is very likely to adversely affect human life-quality and longevity, forever or for very long periods, something that should loom larger in longtermist concerns than it currently does. While some cause areas raise even greater existential risks, or are less neglected, some proposed interventions against climate change could compete well with some in higher-ranked cause areas.

[1] For helpful comments, thanks to Barbara Buckinx, Mark Budolfson, Dan Hausman, Adam Lerner, Lucas Stanczyk, and Bridget Williams.