Based on satellite temperature data collected from 1979 to 2005, American researchers estimate that the Earth’s tropics have expanded by two degrees of latitude, equivalent to 225 kilometers.
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The Sahara Desert is expected to move several hundred kilometers toward the poles. (Photo: NASA) |
Dr. Thomas Reichler, a professor of meteorology at the University of Utah in Salt Lake City and the lead author of the research team, admits they are uncertain whether global warming is the cause of this phenomenon.
“This is indeed a significant change“, Reichler stated: This phenomenon may explain the increase in drought and the decrease in rainfall in recent years in subtropical regions, such as the southwestern United States and the Mediterranean basin of Europe.
“The expansion of the tropical belt could represent a completely new aspect of climate change. We are not sure what triggered it“, Reichler acknowledged.
In addition to global warming, another possible cause is the depletion of the stratospheric ozone layer due to pollutants.
Meteorologists have long defined the tropics as lying between 30 degrees North and 30 degrees South latitude. However, according to observations by Reichler and his colleagues, in both hemispheres at these mid-latitudes, the lower atmosphere near the ground (or troposphere) has become warmer compared to other latitudes over the past 26 years, while the stratosphere has cooled.
The research team believes this change has pushed the rotating tropical jet streams toward the poles.
“These jet streams mark the edge of the tropical region, so if they are moving toward the poles, it means the tropics are expanding“, co-author John Wallace noted. He suggested that the shift of these jet streams will have long-lasting effects on rainfall patterns.
Wallace predicts that the tropical belt will “move an additional 2-3 degrees toward the poles this century, while extremely arid regions like the Sahara Desert may advance even further toward the Earth’s ends, possibly hundreds of miles“.
T. An
