Pollution and warming

(September 2000)

A study carried out at the Massachusetts Institute of Technology (MIT) and published in the September 27 issue of the Journal of Geophysical Research - Atmospheres, indicates that, although urban air pollution is expected to increase significantly in the coming century, it will not have a big effect on global temperature change. In other words, while there may be temperature increases in certain regions, global mean surface temperature will not go up significantly because of urban air pollution.

The researchers reached this conclusion using a method that allows global coupled-chemistry climate models to take urban air pollution into account in a new way. They found a complex interaction in the troposphere between methane and ozone that should largely make the concentrations of these gases cancel each other out, so that the current levels (or trends) will not be greatly influenced by pollution.

Previously, most scientists had considered that this would probably be the end result, but now it has been confirmed rather more rigorously. Global climate models like this are used by researchers to predict future conditions and to aid global policy matters such as the Kyoto Protocol. The researchers used the MIT Integrated Global System Model, which includes an economic development model, a two-dimensional land and ocean resolving interactive chemistry-climate model that divides the planet into 24 latitudinal bands, a terrestrial ecosystems model, and a natural emissions model.

This new model leaves the chemistry of urban air pollution out of global climate models, but the researchers do not believe that this makes any significant changes. Among the questions a future more powerful model may help answer: How do air pollution and climate policies interact? What are the long-term effects of regional regulations regarding air pollution? What are the long-term effects or cost savings of targeting only greenhouse gases or more stringent Environmental Protection Agency air pollution regulations?

Population projections show that the concentration of people in urban areas will increase dramatically in the next 100 years. While 30 to 40 percent of air pollution currently comes from urban areas, as much as 70 percent may originate from cities in the future. The researchers carried out three simulations of 100-year projections, each taking about a day on a powerful work station, that factored in the effects of increased urban air pollution tied to population increases and economic development in these areas. They found that, even with significant increases in air pollution, global mean temperature should not change much, although there may be more pronounced regional effects.