I claim that global warming should be viewed as an existential risk to humanity. The trajectory of global temperature is headed to a region where the consequences to humanity are uncertain, but have a large probability tail that includes true catastrophe. But there is an obvious and deflationary objection to this. ‘Existential Risk’ is hyperbolic if global warming is, as I also claim, an outcome that we can both predict and take action to avoid. I could also claim that driving my family down a highway is an existential risk to us, because I could collide with the abutment of a bridge. Well, yes, but isn’t it more likely that when I see the bridge, I will steer around it?
The true risk, then, is that humanity will be so collectively irrational as to fail to take corrective action. Is this plausible?
I think there is a significant chance that we will not take corrective action in time to prevent catastrophic environmental damage. Leaving aside vital questions of global justice, there are four key problems.
The first problem is that we are facing one or more critical limit values in the atmospheric concentrations of greenhouse gases. There are values for, say, atmospheric CO2 which are
…(1) the tipping level, the global climate forcing that, if long maintained, gives rise to a specific consequence, and (2) the point of no return, a climate state beyond which the consequence [catastrophic climatic change] is inevitable, even if climate forcings are reduced. A point of no return can be avoided, even if the tipping level is temporarily exceeded. Ocean and ice sheet inertia permit overshoot, provided the climate forcing is returned below the tipping level before initiating irreversible dynamic change.
Alternatively, if we overshoot these values for a sustained period the temperature will increase explosively.
The second problem is that we are not certain what these values are. It is possible that we have some time before we reach the tipping point or the point of no return. It is also possible that we have already passed the tipping value for the concentration of CO2.
Regardless, the third problem is that the economic processes that generate additional CO2 are massive, move at high velocity, and thus have enormous momentum. It takes a large and prolonged force to slow and stop a system with high momentum. Suppose that to limit temperature growth to X degrees centigrade requires that we halt the concentration of CO2 at Y parts per million. But the momentum of global energy production means that if you wish to stop CO2 concentration at Y ppm, you must begin applying massive braking force long before CO2 concentration reaches Y. Charles Mann points out that this is like steering a supertanker:
…the ship is too large to turn quickly… [For example,] carbon-sequestration techniques and nuclear power plants cannot be deployed instantly. Changes must be planned and executed decades in advance of the usual signals of crisis, but that’s like asking healthy, happy sixteen-year-olds to write living wills.
Finally, this application of the brakes involves unprecedented self-denial on the part of the species. Burning the accessible fossil fuel will with certainty put us above the tipping point and the point of no return. We have to leave burnable coal and oil in the ground. Charles Mann again:
Not only is the task daunting, it’s strange. In the name of nature, we are asking human beings to do something deeply unnatural, something no other species has ever done or could ever do: constrain its own growth (at least in some ways). Zebra mussels in the Great Lakes, brown tree snakes in Guam, water hyacinth in African rivers, gypsy moths in the northeastern U.S., rabbits in Australia, Burmese pythons in Florida—all these successful species have overrun their environments, heedlessly wiping out other creatures. Like Gause’s protozoans, they are racing to find the edges of their petri dish. Not one has voluntarily turned back. Now we are asking Homo sapiens to fence itself in.
The upshot is that there is a real probability that we are heading toward the bridge abutment, with high momentum, right now. Do we even see this abutment? As has been frequently observed, climate change was not discussed in the 2012 US election. Coincidentally, but nearly unnoticed, the Doha meeting of the United Nations Framework Convention on Climate Change also occurred in November of 2012.
The Doha meeting seems to have accomplished two things. There was, first, an agreement that the Kyoto Protocol will remain in force until 2020. This is not the massive braking force that we need to halt the momentum of greenhouse gas emissions, in that the Kyoto Protocol covers only 15% of global carbon emissions. Second, the Doha meeting agreed that an agreement to replace Kyoto will be specified in 2015, and be implemented by 2020. So in the best case, we will start to apply the braking force in three to seven years. But it is hard for me to imagine that we will have global agreement on a comprehensive solution to greenhouse gas emissions in two years. ‘Existential Risk’ is not hysterical rhetoric.