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要旨:
Climate and atmospheric CO2 concentration
are intimately coupled in the Earth system: CO2 influences climate through the greenhouse effect, but climate also
affects CO2 through its impact on the amount of carbon
stored on land and in the ocean. The change in atmospheric
CO2 as a response to a change in temperature (DCO2=DT)
is a useful measure to quantify the feedback between the
carbon cycle and climate. Using an ensemble of experiments
with an Earth system model of intermediate complexity
we show a pronounced time-scale dependence of
DCO2=DT. A maximum is found on centennial scales with
DCO2=DT values for the model ensemble in the range 5–12
ppm C-1, while lower values are found on shorter and
longer time scales. These results are consistent with estimates
derived from past observations. Up to centennial
scales, the land carbon response to climate dominates the
CO2 signal in the atmosphere, while on longer time scales
the ocean becomes important and eventually dominates on
multi-millennial scales. In addition to the time-scale
dependence, modeled DCO2=DT show a distinct dependence
on the initial state of the system. In particular, on
centennial time-scales, high DCO2=DT values are correlated
with high initial land carbon content. A similar
relation holds also for the CMIP5 models, although for
DCO2=DT computed from a very different experimental setup. The emergence of common patterns like this could prove to usefully constrain the climate–carbon cycle feedback.
