Every happy family is alike; every unhappy family is unhappy in its own way.
Leo Tolstoy, Anna Karenina
Apropos of the Anna Karenina Principle, how many things would have to go right for climate change to be merely an expensive annoyance (or one human problem among many), rather than a planetary disaster?
First, we need continued rapid economic growth. Even in the best case, dealing with the impacts of global warming -- drought, sea level rise, heat waves, extreme weather events -- between now and 2100 or 2200 will require resources we don't have today. Without continual economic growth, even most optimistic global scenarios offer certain disaster.
The assumption of continued economic growth is a reasonable one, as the world's economy has been on an upward trend for many years:
It is necessary but not sufficient that climate sensitivity prove to be on the low end of estimates. With a climate sensitivity of 3C, and a BAU pathway of 1000ppm CO2 equivalent (1), we can expect +4-6C of warming, which would wipe out most forms of life on earth.
|Extract from p. 42 of Technical Summary of IPCC WGIII Fourth assessment Report (2007)|
Reasonable people trying to strike a middle course between "alarmism" and "skepticism" will often say that climate change may not be a big deal, but we should protect ourselves from the possibility that climate sensitivity is high. This is well-intended, but a wrongheaded oversimplification. The reality is that while five degrees and onward is a planetary catastrophe under almost any set of assumptions you chose does not mean that 2-3 degrees is an expensive but manageable problem. A high total temperature rise is game over; a low total temperature rise still requires many other things to go right (2).
Sea level rise is presently estimated at between 0.5m to 2.0m between now and 2100. It needs to be closer to 0.5m to avoid the loss of huge numbers of human settlements to the sea. We must hope that the Greenland ice sheet and the WAIS respond very slowly to warming and are largely incapable of responding on a decadal scale. Of course other ice sheets, such as the less-popular sibling of the West Antarctic ice sheet, the East Antarctic ice sheet, must not have any nasty surprises in store.
Agriculture will have to prove highly resistant to climate shocks. Varying the type of crops and making efficient irrigation broadly available while avoiding massive losses to pests, diseases, and extreme precipitation.
We cannot afford to lose the Amazon (as is expected) or the boreal forests: the Anna Karenina scenario requires they resist warming and there is no massive die-off that would turn the terrestrial biosphere into a net source of carbon. That would insure catastrophic long-term warming.
No Arctic warming tipping points.
Healthcare technology and delivery systems will have to advance faster than the spread of tropical diseases north and south. Efficient building designs and/or air conditioning will need to be available to rich and poor alike to avoid millions of deaths from the direct thermal effects alone.
Permafrost melting will need to release its stored carbon slowly, and overwhelmingly as carbon dioxide and only a small amount as methane. Methyl hydrates need to stay put, or leak out only very slowly.
Political systems will have to prove highly resilient and adaptive. They will have to respond to the escalating climate harms with aggressive long-term adaptation, and not make things worse with panic responses like hoarding, protectionism, or conflicts over migration, borders, or resources. As the Economist cogently put it:
I feel fairly comfortable arguing that a modern economy can handle the stresses of climate change reasonably well; economies are built to handle big change. I feel very nervous about the ability of various political systems to survive temperatures unprecedented in human history. Many political systems rely explicitly on stability to survive, and even those capable of handling climate impacts may struggle to handle the knock-on effects of climate impacts on their more vulnerable neighbours. And as political systems are disrupted, it will become more difficult to sustain growth.This is a partial list. There are impacts I haven't covered; there are certain to be impacts no one has yet guessed at.
The nasty aftertaste of a clear-eyed look at the possibilities is this: even if everything goes right -- if humanity holds the winning climate lottery ticket and none of the terrible things come to pass, or happen only in a blunted and delayed form, and only (in large part) after we are all healthier and wealthier and wiser than we are today: even so, in the best of all possible worlds, global warming will be an expensive destructive mess than will drag on for thousands of years, making the impoverishment of the natural world and disruption of the benign Holocene climate our civilization's permanent legacy.
Most economic analyses assume all these good things happen and neglect, not out of malice but due to the limitations of their science, most of the horrible disasters climate scientists think are possible -- in some cases likely. Even so, the benefits of slowing climate change outstrip the costs in virtually every economic analysis out there.
One of my least favorite lukewarmer fallacies is the concept of "no regrets" policies -- that we should push ahead with policies that can be sold to the right wing as energy independence or job creation or whatever appeals to those in denial of the science. This is an asinine idea. Climate change is real. You don't get to smart policy by agreeing to disagree on critical scientific facts pertaining to the future of human civilization. Here's the truth; aggressive emissions cuts are the true no-regrets strategy. Uncertainty in climate change lies between bad and worse. The benefits range from saving trillions of dollars and millions of lives, on the low side, to averting planetary catastrophe.
1) Meaning a forcing caused by human activities similar to change the level of CO2 to 1000ppm, comprised mostly of CO2 but also with contributions from methane, NO, CFCs, and land use changes.
2) The best analysis of the economic implications of a "fat tail" probability of climate catastrophe is "On modeling and interpreting the economics of catastrophic climate change" (2009) by Martin L. Weitzman, the undisputed expert in this area (400+ citations for that paper alone in less than three years). He wisely make the limitations of climate sensitivity highly explicit:
There are so many sources of uncertainty in climate change that a person almost does not know where or how to begin cataloging them. For specificity, I focus on the uncertainty of so-called "equilibrium climate sensitivity." This is a relatively well-defined and relatively well-studied example of known unknowns, even if the uncertainties themselves are uncertain. However, it should be clearly understood that under the rubric of "equilibrium climate sensitivity" am trying to aggregate together an entire suite of uncertainties, including some non-negligible unknown unknowns. So climate sensitivity is to be understood here as a prototype example or a metaphor, which is being used to illustrate much more generic issues in the economics of highly uncertain climate change.