Over the past 27 years, the tropics have expanded their reach, according to scientists who have analyzed temperatures recorded by satellites.

Qiang Fu, a professor of atmospheric sciences at the University of Washington, and his colleagues report in tomorrow’s issue of the journal Science that the temperature of the lowermost atmosphere has warmed more at 30 degrees latitude north and south than at the equator. That warming has pushed the westerly jet streams in each hemisphere further from the equator by one degree of latitude since 1979.

The researchers cannot say whether such changes are related to the effects of greenhouse-gas pollution and whether they will continue, but Mr. Fu says it is likely that the tropical changes are linked to global warming.

The expansion of the tropics may have profound significance because many deserts are located at the edges of the tropics. The recent changes might cause those dry regions to spread north and south of their current positions, suggest the researchers.

“This would enhance the probability for drought events in the higher latitudes,” around 30 degrees north and south of the equator, says Mr. Fu. Such droughts could hit the southwestern United States, southern Europe, South China, Australia, and South Africa, he says.