New perspective article provides recommendations on how to calculate remaining carbon budgets in a transparent way, and discusses their uncertainties and implications for both international and national climate policies.
Global warming is proportional to the total amount of CO2 emitted. The more we emit, the higher the global mean temperature will be. This simple yet powerful relationship has important implications for international policies to stabilize climate and underlines the need to set national and regional net-zero emission targets, where remaining emissions are offset by artificial carbon dioxide removal from the atmosphere.
A new perspective published in Nature Geoscience, which has been supported by the 4C project, offers an overview of the current knowledge surrounding remaining carbon budgets, which represent the total amount of CO2 that can still be emitted in the future while limiting global warming to a given temperature goal, such as meeting the Paris Agreement target.
There is more than one way to calculate the remaining carbon budgets. Actually, recent studies have estimated that the allowable amount of additional emissions was larger than previously thought. This uncertainty can be used to either trivialize the most ambitious mitigation targets by characterizing them as impossible, or to argue that there is ample time to allow for a gradual transition to a low-carbon economy.
Neither of these extremes is consistent with our best understanding of the remaining carbon budget, according to the new perspective led by Damon Matthews. Understanding the scientific and socio-economic uncertainties affecting the size of the remaining carbon budgets, as well as the methodological choices and assumptions that underlie their calculation, is essential before applying them as a policy tool.
Need for international cooperation between scientists and policy makers
Paris Agreement sets national emission targets but resulting reductions in global emissions are insufficient to meet the overall target. In order to use the remaining carbon budgets to a more fair and ambitious distribution of mitigation effort among countries, international cooperation and oversight is key. Thus, scientists must work together with policy makers to align the future target setting with the remaining carbon budgets as a way to improve and strengthen national climate policies.
Fairness principles that could guide a distribution of the global remaining carbon budget to national allocations.
To stabilize global temperatures at any level, we need to eliminate net CO2 emissions. To better inform this overall policy goal, the scientific community needs to continue working to improve understanding of uncertain processes, as well as to calculate remaining carbon budgets in a consistent, clear and transparent way.
From a societal point of view, it is important to see the remaining carbon budget as a global limit on emissions, representing a collective effort that we all need to contribute to achieving. All countries have a role to play in this collective goal, and only with a concerted near-term effort by all of us will we retain any reasonable chance of meeting the temperature goals of the Paris Agreement.
Study: Matthews H.D., Tokarska K.B., Nicholls Z.R.J. et al. (2020). Opportunities and challenges in using remaining carbon budgets to guide climate policy. Nat. Geosci. 13, 769–779. DOI: 10.1038/s41561-020-00663-3