Chapter 2, "The Climate Challenge"

This chapter explores the implications of the climate science for climate mitigation and explains why the potential for severe, irreversible effects argues for assigning urgency and priority to the pursuit of emissions reductions.

Some aspects of the climate science are deeply uncertain, but sufficient evidence exists to conclude that anthropogenic climate change will cause substantial harms, and atmospheric carbon dioxide levels will remain elevated for thousands of years. Climate change is thus largely irreversible, and if we wait to resolve all uncertainties we will be stuck with the consequences for generations. In fact, the world may have missed its chance to keep warming below the 2°C goal adopted in the Paris agreement, but ensuring that the world’s temperature exceeds 2°C by as a little as possible can reduce the risk of crossing tipping points. Even if all nations fulfill the commitments made in the Paris agreement, this will leave the Paris Gap—a shortfall of roughly 30 to 90 billion tons over the next decade between the Paris agreement pathway and the pathway necessary to keep warming below 2°C. Complementary mitigation measures such as private governance are thus an important part of the response to climate change.