Globally, the temperature trend from January 1979 through December 1998 was warming at the rate of about 0.06 Celsius per decade. That split saw the Northern Hemisphere warm by about 0.2 C in 20 years, while the Southern Hemisphere got neither warmer nor cooler. Almost all of North America, the North Atlantic and Europe saw temperatures warm slowly from 1979 through 1998. At the same time, 20-year cooling trends were found over Labrador, Antarctica, most of the Southern oceans, and a region stretching eastward from Central Africa across the Middle East, the Indian subcontinent and Southeast Asia. Burning coal, petroleum products, natural gas and wood returns carbon dioxide to the atmosphere.
Carbon dioxide is a greenhouse gas which traps heat rising from Earth's surface.
In recent years, climate scientists have theorized that the additional carbon dioxide might create an enhanced greenhouse effect, which would cause global warming. While carbon dioxide levels in the atmosphere have risen in recent years due to burning fossil fuels, the extra CO2 gas has generally spread almost evenly around the globe instead of concentrating in the Northern Hemisphere. What does stay in the atmosphere over the Northern Hemisphere is sulfate pollution caused by burning fossil fuels, Christy said. Sulfate particles, which generally stay in the atmosphere less than two weeks, reflect sunlight back into space. This should cause a cooling effect that would be strongest near and down wind from the site of the pollution.