U. professor notes tropics expansion

A study by scientists at the Universities of Utah and Washington says tropical-zone weather patterns have expanded by two degrees latitude since 1979, which may mean the tropics have widened by 140 miles.

Whether that is a result of global warming or some other factor, the authors can't say. But the startling fact is published in today's edition of Science Magazine, in a report titled, "Enhanced Mid-Latitude Tropospheric Warming in Satellite Measurements."

The magazine is published by the American Association for the Advancement of Science and is one of the world's most respected science journals.

"The Earth is warming faster in the mid-latitudes than it is . . . in the tropics," said Thomas Reichler, assistant professor of meteorology at the University of Utah and one of the report's authors.

The satellite readings used in the study extended from 1979 until 2005.

"We take satellite measurements of atmospheric temperatures," Reichler said. "And we'll take longtime series of those measurements."

The readings show significant temperature changes have occurred in the region between 15 degrees and 45 degrees latitude, in both northern and southern hemispheres.

There, the stratosphere — the region of the atmosphere between six and 15 miles above Earth's surface — has been cooling. At the same time, the troposphere — the atmosphere between the surface and the stratosphere — has been warming. The changes were "relative to other latitudes," the study says.

These changes are "a robust feature of the period of record from 1979 onward," the report says, and are not caused by a short-term fluctuation, such as the record temperatures that happened in the summer of 1998 because of the El Nino weather system.

"You get pronounced warming in the mid-

latitudes," said Reichler, referring to the region between 30 degrees and 45 degrees, both in the northern and southern hemisphere.

That means much of the Earth is warming at the surface, as scientists have observed for years. What is new is that Reichler and the other researchers infer that changes have reshaped the tropical jet streams, moving them 1 degree closer to the pole, on each side of the equator. This could mean the tropics have expanded by 140 miles.

Is the cause of this warming prompted by the so-called greenhouse effect?

"We don't really know yet what the reason is," Reichler told the Deseret Morning News.