Gian-Kasper Plattner and colleagues (J. Clim. 21, 2721–2751; 2008) provide at least a broad sense of direction by simulating our commitment to future climate change with eight climate–carbon cycle models of intermediate complexity, assuming a number of different scenarios for future carbon dioxide emissions. In all the scenarios, atmospheric carbon dioxide concentrations are either constant or in decline after the end of the 21st century, providing us with an idea of how long the effects of carbon dioxide emissions will linger after atmospheric concentrations have stabilized.
Perhaps the most striking result is that the year AD 3000 — the time limit of the simulations — is apparently too close in time for a full assessment. Even in the highly unlikely event that anthropogenic emissions stop in the year 2100, 15–28% of the carbon dioxide emitted through human activity since the industrial revolution will still be airborne 900 years later. For a stabilization of atmospheric carbon dioxide concentrations at 750 p.p.m.v. — a goal that looks achievable if not desirable from today's point of view — temperatures start declining fairly soon after stabilization, but they do so very slowly. Even worse, the sea level rise resulting from thermal expansion alone (that is, not taking into account meltwater from the Greenland ice sheet or elsewhere) does not come to a halt by the year 3000 in some of the models.
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