evidence: Short-lived climate forcers have long-term climate impacts via the carbon–climate feedback [...] where \(\alpha \equiv \Delta T_A/\Delta C_A\) is the sensitivity of climate to atmospheric CO2 (in a unit of K GtC−1), which represents the change in temperature in response to a change in CO2 concentration7,19. The α is a useful measure to quantify the feedbacks between climate and carbon cycle over both preindustrial and industrial periods. The \({\mathrm{TCRE}} \equiv \Delta T_A/\Delta C_E\) is transient climate response to cumulative CO2 emission (in a unit of K GtC−1)20, which quantifies the ratio of change in temperature to cumulative carbon emissions, providing another useful measure to estimate the total allowable emissions for a given temperature change, as there is a near-linear relationship between cumulative CO2 emissions and global temperature change20.