Geoengineering—the deliberate modification of the environment on a large scale—is an important strategy to consider, but many of its forms are last resort alternatives. Some forms of geoengineering, like carbon sequestration, are probably going to be important parts of the solution. Carbon sequestration involves injecting carbon dioxide into rock layers deep underneath the Earth’s surface, in some cases into the very same fossil fuel reservoirs we got the carbon from in the first place. On the more farfetched side are schemes such as blocking sunlight by deploying millions of small mirrors into space or releasing sulfate particles to replicate the cooling effects of a volcanic eruption. Some of these seem wildly impractical, and don’t get at the root causes of climate change. And they could have unintended consequences that produce disastrous effects. On top of all of this is the ethical question of who decides for all humanity to deliberately change the climate.

In the short term, a recession can reduce emissions by curtailing economic activity. U.S. carbon dioxide emissions went down in both 1991 and 2001 due to economic slowdowns. However, emissions returned to previous levels once the economy picked up, and atmospheric CO₂ concentrations continued rising. Improvements in energy efficiency that require a one-time startup cost (such as installing solar panels) may be delayed or cancelled during an economic slowdown, which would only postpone addressing the problem.