Abstract
The remaining carbon budget quantifies the future CO2 emissions to limit global warming below a desired level. Carbon budgets are subject to uncertainty in the Transient Climate Response to Cumulative CO2 Emissions (TCRE), as well as to non-CO2 climate influences. Here we estimate the TCRE using observational constraints, and integrate the geophysical and socioeconomic uncertainties affecting the distribution of the remaining carbon budget. We estimate a median TCRE of 0.44 °C and 5–95% range of 0.32–0.62 °C per 1000 GtCO2 emitted. Considering only geophysical uncertainties, our median estimate of the 1.5 °C remaining carbon budget is 440 GtCO2 from 2020 onwards, with a range of 230–670 GtCO2, (for a 67–33% chance of not exceeding the target). Additional socioeconomic uncertainty related to human decisions regarding future non-CO2 emissions scenarios can further shift the median 1.5 °C remaining carbon budget by ±170 GtCO2.
Highlights
The remaining carbon budget quantifies the future CO2 emissions to limit global warming below a desired level
Remaining carbon budgets (RCBs) represent the future cumulative CO2 emissions that would be consistent with keeping global warming to a specified level, such as those mentioned in the Paris Agreement[1,2,3,4], and play an important role in framing the objectives of national and international climate policy
Given the relevance of carbon budgets to inform climate policy discussions and decisions[14], it is essential that the key uncertainties associated with the RCB are understood and quantified and integrated into its main estimate
Summary
The remaining carbon budget quantifies the future CO2 emissions to limit global warming below a desired level.
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