Published in Carbon Brief
The concept of a “carbon budget” has proved to be both elegantly simple and stubbornly complicated.
The theory dictates that the total amount of CO2 emitted until emissions are taken down to zero determines the maximum warming that the world will subsequently experience. This was the promise from a series of seminal studies published nearly a decade ago.
Our latest understanding of climate science teaches us that this promise is still largely kept, but it turns out things are not quite so straightforward when estimating how much carbon budget remains if we want to cap warming to a precise level. The estimated size of the remaining carbon budget can depend on a whole range of factors, which makes it much trickier to compare different estimates directly.
As authors on the Intergovernmental Panel on Climate Change’s special report on 1.5C of global warming (SR15), part of our task was to bring the different carbon budget estimates together.