Recent estimates of the amount of carbon dioxide that can be emitted whilst still achieving the Paris Agreement temperature goals are larger than previously thought.
However, the Paris Agreement did not specify which temperature metric or baseline should be used, making the concept of the remaining carbon budget open to different interpretations. So which temperature metrics should be used?
This Nature perspective from CONSTRAIN authors Kasia Tokarska, Carl-Friedrich Schleussner, Joeri Rogelj and colleagues provides some answers, alongside guidelines on the use of different temperature metrics for estimating remaining carbon budgets.
The article discusses both methodological choices around how global mean temperature is calculated, as well as the choice of reference period, and how these choices influence estimates of the remaining carbon budget.
Overall, the choice of the temperature metric depends on the application: scientific estimates of the total or remaining carbon budgets should use globally averaged surface air temperature (GSAT), but progress towards the Paris Agreement goal should use a hybrid temperature metric consistent with the science that the Agreement was based upon.
Different choices and recommendations for the use of global mean temperature metrics (simplified)