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A revised estimate of the processes contributing to global warming due to climate‐carbon feedback
Author(s) -
Cadule P.,
Bopp L.,
Friedlingstein P.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl038681
Subject(s) - greenhouse gas , climate change , environmental science , radiative forcing , climate commitment , climatology , carbon cycle , global warming , runaway climate change , atmospheric sciences , climate model , carbon fibers , coupled model intercomparison project , atmosphere (unit) , effects of global warming , meteorology , geography , ecology , ecosystem , mathematics , physics , algorithm , composite number , biology , geology
Coupled climate‐carbon cycle models have shown that anthropogenic climate change has a negative effect on natural carbon sinks i.e., climate change induces a reduction in both land and ocean carbon uptake leading to an additional amount of CO 2 in the atmosphere. Friedlingstein et al. (2006) concluded that such supplementary CO 2 in the atmosphere would lead to an additional climate warming in 2100. However, as given by Friedlingstein et al. (2006), the role of non‐CO 2 greenhouse gases (GHGs) and aerosols was neglected both for their direct impact on climate and their indirect impact on the carbon cycle. Besides, the climate models used for IPCC AR4 accounted for the radiative forcing of all GHGs and anthropogenic aerosols but neglected the climate‐carbon cycle feedback. In IPCC AR4, Meehl et al. (2007) attempted to reconcile these two methods in order to derive the global warming that would arise from both all anthropogenic forcings and climate‐carbon cycle feedback. Here we show that the approach they used is wrong for several reasons. First, as previously done by Friedlingstein et al. (2006), they considered that the warming is proportional to the change in atmospheric CO 2 concentration. This assumption leads to consider that the gain in temperature is equal to the gain in CO 2 . However, because of the non‐linearity of the climate response to increased CO 2 concentrations, the gain in temperature is lower than the gain in CO 2 . Second, they assumed that the temperature gains of the climate‐carbon cycle feedback generated by CO 2 , non‐CO 2 GHGs and aerosols are all equal. We show here that, because of the specific spatial and temporal distribution of the radiative forcing exerted by those external perturbations, the temperature gains are all different. Based on our revised method, we found that, for the SRES A2 scenario, the projected global warming in 2100, due to increases in atmospheric CO 2 , non‐CO 2 GHGs and anthropogenic sulphate aerosols, is 2.3–5.6°C. This is accidentally nearly equal to the original one of Meehl et al. (2007) (2.4–5.6°C).