Here I present a simple, transparent, three compartment model with two observationally determined parameters, describing uptake of atmospheric CO₂ by the global ocean. Extension of this model permits examination of « what if » questions, importantly, response of atmospheric CO₂ to abrupt cessation of emissions, to determine the lifetime of excess atmospheric CO₂.

In Praise of Simple Models

Carbon dioxide is the most important greenhouse gas forcing climate change over the Anthropocene. Consequently, the amount and budget of atmospheric CO₂ are very important to understanding its climate effects. Current models of how atmospheric CO₂ would decrease in response to changes in emissions are highly uncertain. Where does the emitted CO₂ go? There are only two sinks: the global ocean and the terrestrial biosphere. Here I present a simple, transparent, three compartment model with two observationally determined parameters, describing uptake of atmospheric CO₂ by the global ocean. When forced by observed atmospheric CO₂ this simple model compares to available observations of ocean uptake of carbon and radiocarbon as well as, or better than, much more complex models. Extension of this model to the terrestrial biosphere requires two additional parameters, both constrained by observations. This extended model permits examination of « what if » questions, importantly, response of atmospheric CO₂ to abrupt cessation of emissions, to determine the lifetime of excess atmospheric CO₂. The resulting 1/e lifetime, range 90-150 years, is much shorter than other recent estimates. If this estimate is correct, atmospheric CO₂ and climate, would, encouragingly, respond to changes in CO₂ emissions on the time scale of a human lifetime.

Séminaire en anglais.

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