Scientists have observed for years that the Earth's tropics are widening in connection with complex changes in climate and weather patterns. But in recent years, it appeared the widening was outpacing what models predicted, suggesting other factors were at work. A new paper co-authored by Indiana University Bloomington researcher Paul Staten, however, finds that the most up-to-date models and the best data match up reasonably well.
The paper, "Re-examining Tropical Expansion," was published in the journal Nature Climate Change. Additional authors include Jian Lu of the Pacific Northwest National Laboratory, Kevin Grise of the University of Virginia, Sean Davis of the National Oceanic and Atmospheric Administration in Colorado and Thomas Birner of Ludwig Maximilians University Munich in Germany.
Staten said the research should add confidence to predictions based on current climate models.
"Climate change should continue to expand the tropics over the next several decades," he said. "But the expansion may not continue at the rapid rate we've seen; at times it may even temporarily contract."
The authors conclude that the tropics have been widening at an average rate of about 0.2 degrees latitude, or about 17 miles, per decade in both the Northern and Southern hemispheres. The rate varies widely from year to year and from location to location.
Widening of the tropics is important because it could be associated with severe changes in climate, Staten said. The world's hot, dry deserts tend to be located in bands along the northern and southern edges of the tropics, so widening of the tropics could lead to expansion of the subtropical deserts. At sea, the edges of the tropics are zones of high salinity and low marine productivity.