Research update

Knowledge Gain: On updated carbon budget estimates with the latest insights on forcing, variability and feedbacks

CONSTRAIN’s new report on the remaining carbon budget provides an update to the budget itself alongside insights on radiative forcing, variability and feedbacks.

The remaining carbon budget is our best estimate of the amount of carbon dioxide that can be released before we expect to reach a certain temperature at a given probability – for instance, a 50% probability budget for keeping warming to 1.5°C.

Integrating the latest scientific evidence into estimates of the remaining carbon budget has reduced its size: the most up-to-date estimate of the remaining carbon budget that would provide a 50% probability of limiting global warming to 1.5°C, starting from 2023, is now 250 GtCO2 – around 6 years of current emissions.

This number has fallen by half since the IPCC AR6 Working Group I report was published in 2021.

Incorporating additional uncertainties, such as the warming we can expect after CO2 emissions reach net zero, also limits confidence that the current carbon budget for staying within 1.5°C is still a positive number.

Significant non-CO2 emission reductions (of methane in particular) are also needed if the world is to stay within the remaining carbon budget for 1.5°C.  Overall, global emissions must decline sharply and immediately to keep the Paris Agreement temperature goals in sight.