Sulphur Cycle Experiment

This experiment adds a fully interactive sulphur cycle to the model used in the climateprediction.net experiment. This will help us to identify the effects of sulphate aerosol on the global climate system and the sensitivity of the model to perturbing sulphur cycle parameters. For this new experiment, an extra 2 phases will be added to the 3 phase experiment 1. In one extra phase, the sulphate emissions will be changed to those expected in 2005, and in the other both sulphate and carbon dioxide will be changed. In addition, the sulphate emissions typical of 1985 will be included in the first 3 phases. This experiment will be available for download for a limited period of time, just like the thermohaline experiment we ran in 2004.

Sulphates act to scatter solar radiation and reduce the amount of solar energy reaching the surface. The reduction in solar radiation cools the surface and reduces the warming effect caused by greenhouse gases. So, a prediction of the climate in the 21st century needs to contain the effects of sulphate aerosol otherwise the warming trend may be overestimated - the so-called 'global dimming' effect.

From this experiment it is hoped that we will be able to better understand the range of uncertainty in climate models due to the parameters in the sulphur cycle. This information will then be used in climateprediction.net experiments 2 & 3.

Figure 1 shows one model's surface temperature response to increasing sulphur emissions from pre-industrial levels (natural) to present day levels (natural plus anthropogenic). The cooling effect of sulphate aerosol can be seen throughout the whole northern hemisphere and corresponds to the high sulphate burden of the northern hemisphere shown in Figure 2.

Figure 2 shows the 1985 distribution of sulphate in the atmosphere over the North Atlantic, North America and Europe. The regions of high anthropogenic source emissions of sulphur dioxide leads to high concentrations of sulphate aerosol over the northern hemisphere continents. Unlike greenhouse gases, the distribution and concentration of sulphates varies a lot with location, as can be seen by comparing the sulphate concentration over the North Pole with that over North America.