Worst Case for Climate Change Doesn’t Look Realistic

In recent years, much of the commentary about climate change has gone from sternly serious to wildly despairing. A new report from the United Nation’s Intergovernmental Panel on Climate Change warns that the effects of climate change are accelerating and that the world has barely more than a decade to make deep cuts to greenhouse gas emissions and limit warming to 1.5 degrees Celsius by century’s end. Such reductions are extremely unlikely, given that global emissions rose this year and last. China, the world’s biggest emitter by far, is still building coal-fired power plants, while the U.S. under President Donald Trump has abdicated leadership on the climate issue. Warming of more than 1.5 degrees seems certain at this point and the world will have to deal with the consequences.

But how much, exactly, will Earth warm before the fossil-fuel era runs its course? That’s harder to forecast because it depends not just on climate science but also on assumptions about emissions. And that, in turn, depends on technology and economics, both of which are notoriously hard things to predict. The IPCC lays out several business-as-usual scenarios for how much greenhouse gas would be emitted without major policy action, but it doesn’t say which scenario it thinks is more likely. The direst of these, called RCP8.5, implies that the planet would warm by an average of 5 degrees Celsius (about 9 degrees Fahrenheit) by 2100 -- an absolutely catastrophic, civilization-ending level of warming. It’s typically this doomsday scenario that motivates some observers to despair and others to call for reckless, flailing policies like the dismantling of capitalism.