Halting CO2 emissions is predicted to stabilize global surface temperatures over multi-century timescales. However, a study published online in Nature Climate Change now reports that within the next 500 years, after an initial century of decline, temperatures may then continue to increase.

Thomas Froelicher and colleagues use an Earth system model to simulate how global temperature will change after an 1,800 Gt carbon pulse, which increases atmospheric CO2 concentrations to quadruple that of the pre-industrial world. They find that the carbon injection causes a peak in warming 15 - 20 years after the event, followed by a temperature decrease to 1.5 °C above pre-industrial temperatures in the first 100 years. This initial cooling effect is caused by decreasing atmospheric CO2 concentrations and thus more heat can be radiated back to space from Earth. Surprisingly, the model projects warming of 0.37 °C between 100 and 500 years after the carbon injection, which the authors attribute to the weakening of the ocean heat uptake.

These results highlight the uncertainty associated with both the projection of regional ocean heat uptake and responses of surface temperature to cumulative carbon emissions.