Carbon Cycle Response to Temperature Overshoot Beyond 2°C: An Analysis of CMIP6 Models
Résumé
There is a substantial gap between the current emissions of greenhouse gases and levels
required for achieving the 2°C and 1.5°C temperature targets of the Paris Agreement. Understanding
the implications of a temperature overshoot is thus an increasingly relevant research topic. Here we
explore the carbon cycle feedbacks over land and ocean in the SSP5-3.4-OS overshoot scenario by using
an ensemble of Coupled Model Intercomparison Project 6 Earth system models. Models show that after
the CO2 concentration and air temperature peaks, land and ocean are decreasing carbon sinks from the
2,040s and become sources for a limited time in the 22nd century. The decrease in the carbon uptake
precedes the CO2 concentration peak. The early peak of ocean uptake stems from its dependency on
the atmospheric CO2 growth rate. The early peak of the land uptake occurs due to a larger increase in
ecosystem respiration than the increase in gross primary production, as well as due to a concomitant
increase in land-use change emissions primarily attributed to the wide implementation of biofuel
croplands. The carbon cycle feedback parameters amplify after the CO2 concentration and temperature
peaks due to inertia of the Earth system so that land and ocean absorb more carbon per unit change in the
atmospheric CO2 change (stronger negative feedback) and lose more carbon per unit temperature change
(stronger positive feedback) compared to if the feedbacks stayed unchanged. The increased negative CO2
feedback outperforms the increased positive climate feedback. This feature should be investigated under
other scenarios
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