Search

Negative CO2 emissions are a key mitigation measure in emission scenarios consistent with temperature limits adopted by the Paris Agreement. It is commonly assumed that the climate–carbon cycle response to a negative CO2 emission is equal in magnitude and opposite in sign to the response to an equivalent positive CO2 emission. Here we test the hypothesis that this response is symmetric by forcing an Earth system model with positive and negative CO2 emission pulses of varying magnitude and applied from different climate states. Results indicate that a CO2 emission into the atmosphere is more effective at raising atmospheric CO2 than an equivalent CO2 removal is at lowering it, with the asymmetry increasing with the magnitude of the emission/removal. The findings of this study imply that offsetting positive CO2 emissions with negative emissions of the same magnitude could result in a different climate outcome than avoiding the CO2 emissions. It is commonly assumed that the climate response to CO2 removals is equal in magnitude and opposite in sign to the response to CO2 emissions. The response, however, is asymmetric, meaning that offsetting CO2 emissions with equal removals could lead to a different climate than avoiding the emissions.

An analysis of the regional climate response to cumulative CO2 emissions establishes a clear quantitative link between the total amount of CO2 emitted and the magnitude of local climate warming.

Contributions to historical climate change vary substantially among nations. A new method of quantifying historical inequalities using carbon and climate debts can inform discussions about responsibility for cutting emissions in the future.

A modelling study shows how global temperatures would change if all greenhouse-gas and aerosol emissions were eliminated. The researchers estimate the committed future climate warming associated with past anthropogenic emissions, and provide a critical baseline against which to measure the effect of future emissions.