Tropical Regions Expanding, Climatologists Say

AEN News

Washington - Climatologists say that the tropical regions of the world have been expanding since 1979, but they are unsure of the cause, whether its a natural occurrence or due to global warming caused by man-made pollutants.

American climatologists have been analyzing temperature data collected from satellites over a 26-year span and estimate that the tropical region of the world has expanded by two degrees of latitude, or 225km, during that period. In a paper published in Science magazine's May 26 issue, the climatologists said the expanding tropical regions of the world could explain the drought conditions being observed in the in the subtropical regions in the southwestern United States and Europe's Mediterranean basin over the last several years.

Thomas Reichler, a University of Utah meteorology professor and co-author of the study said, "Its a big deal", when commenting on the expanding tropical regions. While global averages show warming of the lower atmosphere, or troposphere, the new study shows specifically that Earth's mid-latitudes grew about 0.83 degrees Celsius warmer over the past 26 years, researchers said.

Earth has two polar jet streams at polar latitudes, one in each hemisphere, and two subtropical jet streams closer to the Equator, also one in each hemisphere. The data show that the jet streams in both hemispheres have moved toward the poles. The jet streams mark the edge of the tropics, so if they are moving poleward that means the tropics are getting wider, one researcher noted.

We analyzed 26-year-long satellite measurements of atmospheric temperatures and found a distinct and very robust pattern of warming, which suggests that each subtropical jet stream has moved poleward by about one degree latitude," or 110km, Reichler said. Weather balloons confirmed the satellite observation, he added.

"The possible expansion of the tropics may be a totally new aspect of climate change," Reichler said. "We don't know for sure what triggered it." Researchers said that besides global warming, another possible cause for tropical expansion is the depletion of the stratospheric ozone layer due to pollutants such as refrigerant gases.