© NASAA satellite view of the ITCZ. Note the clusters of broken clouds aligned just north of the equator (central/eastern Pacific region) in this image.

New research from the University of Washington indicates that the intertropical convergence zone (ITCZ), which is a persistent band of showers and heavy thunderstorms that produces heavy rainfall near the equator, has been creeping northward for more than 300 years now. The zone, on average, has been moving northward at just less than 1 mile a year.

The ITCZ normally fluctuates between 3 and 10 degrees north of the equator, depending on the time of the year.

Researchers believe that global warming is probably the reason for this northward trend.

© University of WashingtonThe ITCZ is indicated by the band of heavy precipitation (blue/purple colors) over the Pacific.

The new article presents surprising evidence that the intertropical convergence zone hugged the equator some 3 1/2 centuries ago during Earth's little ice age, which lasted from 1400 to 1850, according to the EurekAlert press release.

Sediment cores from Palau, which lies about 7 degrees north of the equator and in the heart of the modern convergence zone, also revealed arid conditions during the little ice age.

In contrast, the researchers present evidence that the Galapagos Islands, today an arid place on the equator in the Eastern Pacific, had a wet climate during the little ice age.

"If the intertropical convergence zone was 550 kilometers, or 5 degrees, south of its present position as recently as 1630, it must have migrated north at an average rate of 1.4 kilometers - just less than a mile - a year," according to Julian Sachs, associate professor of oceanography at the University of Washington and lead author of the paper. "Were that rate to continue, the intertropical convergence zone will be 126 kilometers - or more than 75 miles - north of its current position by the latter part of this century."

If the band continues to migrate at just less than a mile (1.4 kilometers) a year, which is the average for all the years it has been moving north, then some Pacific islands near the equator - even those that currently enjoy abundant rainfall - may be drier within decades and starved of freshwater by mid-century or sooner, according to the EurekAlert report.