Ensemble Simulation of Twenty-First Century Climate Changes: Business-as-Usual versus CO2 Stabilization

Abstract Natural variability of the climate system imposes a large uncertainty on future climate change signals simulated by a single integration of any coupled ocean–atmosphere model. This is especially true for regional precipitation changes. Here, these uncertainties are reduced by using results from two ensembles of five integrations of a coupled ocean–atmosphere model forced by projected future greenhouse gas and sulfate aerosol changes. Under a business–as–usual scenario, the simulations show a global warming of ~1.9°C over the twenty–first century (continuing the trend observed since the late 1970s), accompanied by a ~3% increase in global precipitation. Stabilizing the CO2 level at 550 ppm reduces the warming only moderately (by ~0.4°C in 2100). The patterns of seasonal–mean temperature and precipitation change in the two cases are highly correlated (r » 0.99 for temperature and r » 0.93 for precipitation). Over the midlatitude North Atlantic Ocean, the model produces a moderate surface cooling (1...

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