SO2 emissions reduction may increase global warming

“In the atmosphere, sulphur dioxide gas emitted by burning coal and oil is converted into sulphate aerosols that enhance the reflection of solar radiation, thereby tending to cool Earth’s surface,” said Michael Schlesinger, an atmospheric scientist at the University of Illinois. “In recent studies, we found that decreasing the sulphur dioxide emissions led to significant regional warming in North America, Europe and Asia.”

The studies were based on provisional greenhouse-gas and sulphur dioxide emissions developed by the Intergovernmental Panel on Climate Change. The IPCC is producing a Special Report on Emissions Scenarios, in part as background for the IPCC Third Assessment Report scheduled to be completed in 2001. In the special report there are four scenario families for the future emissions of greenhouse gases and sulphur dioxide.

To explore the potential effects, Schlesinger and colleagues first used a simple climate/ocean model to calculate the change in global-mean surface temperature for the sulphur dioxide emissions of the four Special Report scenarios, as well as for the non-interventionist IS92a scenario of the IPCC Second Assessment Report.

“These global-mean temperatures were then used to scale the geographical distributions of temperature change simulated by our atmospheric general circulation/mixed-layer-ocean model for a tenfold increase in present-day sulphur dioxide emissions, both individually and jointly from six geographical regions,” Schlesinger said.

The increasing sulphur dioxide emissions of the IS92a scenario result in a cooling contribution that helps to offset some of the greenhouse gas-induced warming, Schlesinger said, but the decreasing sulphur dioxide emissions of the four SRES scenarios result in the opposite: a significant warming of portions of North America, Europe and the North Atlantic, and Siberia.

“Thus it appears that mitigation of the acid-rain problem by future reductions in sulphur dioxide emissions exacerbates the greenhouse-warming problem by enhancing the warming in and near the regions where the sulphur dioxide emissions are reduced,” Schlesinger said.