The effect of stabilising atmospheric carbon dioxide concentrations on global and regional climate change

The effect on climate of stabilising atmospheric carbon dioxide concentrations at 550ppm and 750ppm is investigated using a coupled ocean-atmosphere model and compared with the response to a baseline case (1% per year increase in carbon dioxide concentrations beyond 1990). Changes in other well-mixed greenhouse gases are not considered (although these are expected to increase in the future), so in practical terms the simulated changes in climate correspond to lower levels of carbon dioxide stabilisation. The global-mean warming between 1990 and 2100 is reduced by 40% and 55% respectively, in close agreement with estimates using energy balance models. Sea-level rise up to 2100 is also reduced, but in the longer stabilisation runs, unlike temperature, sea-level continues to rise throughout the simulations with little reduction of the rate of rise. The patterns of temperature and precipitation change are largely unchanged except that the southern hemisphere warms relative to the northern hemisphere. Changes over five subcontinental regions are considered in more detail. All of the regions, for all of the simulations, show a statistically significant warming by 2100. The reduction in annual-mean warming resulting from stabilisation is also significant by 2100. The seasonal changes in precipitation are significant by 2100 in the baseline simulation but the significance of differences in precipitation between the baseline and stabilisation simulations depends on location and season.