New framework for estimating global carbon budgets

In a recent paper published in Nature, a team of climate scientists have developed a new framework to reconcile disparities in different global carbon budgets to better understand them and more accurately inform climate policy.

The study, Estimating and Tracking the Remaining Carbon Budget for Stringent Climate Targets, was authored by an international team of researchers from the International Institute for Applied Systems Analysis (IIASA), including scientists from the University of Leeds and Imperial College London.

Although the idea of the carbon budget is relatively straightforward – it is the upper limit of how much carbon dioxide (CO2) we can emit in order to stay under a certain temperature threshold, such as the 2°C warming goal of the Paris Agreement – how we get to this figure is very complex. Furthermore, researchers have produced differing estimates using conflicting techniques and criteria, leading to confusion over the variation of results.

The authors of the paper saw these differing estimates and produced a framework to more clearly pinpoint the differences between them. It limits uncertainty by defining the remaining carbon budget by five main factors:
  • the amount of warming expected per tonne of CO2 emission;
  • the current amount of warming observed;
  • the amount of future warming expected from gases and pollutants other than CO2;
  • whether warming stops instantly once CO2 emissions reach zero; and
  • an additional correction for whether there are any feedbacks, such as permafrost thawing, that are not routinely considered.
‘The remaining carbon budget is a key quantity for defining the challenge of limiting climate change to safe levels,’ said lead author Joeri Rogelj. ‘With this paper, we can understand and track this quantity much better. If you carefully look at carbon budgets, they become easy to understand. The fog is lifted, so to speak, and shows even more clearly that the remaining carbon budget to limit global warming to safe levels is tiny – action in the next decade is essential to stay within it.’

A simplified version of the framework has already been used for the Intergovernmental Panel on Climate Change’s (IPCC) 2018 special report, Global Warming of 1.5°C.

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