The researchers state that the tropical zone has increased between 2.0 and 4.8 degrees latitude (both northward and southward) since 1979, which is equivalent to an expansion of between 140 and 330 miles (225 and 530 kilometers) in both directions. This expansion has also been faster than what earlier research had predicted.  Such expansion of the tropics means, in one respect, that the dry subtropical regions of the world would expect to be even more arid in the future.

Besides, Seidel, the co-authors of the study include Qiang Fu (University of Washington, Department of Atmospheric Sciences), William J. Randel (National Consortium for Atmospheric Research, Atmospheric Chemistry Division), and Thomas J. Reichler (University of Utah, Department of Meteorology).

The researchers conclude in their paper’s abstract, “This expansion has potentially important implications for subtropical societies and may lead to profound changes in the global climate system. Most importantly, poleward movement of large-scale atmospheric circulation systems, such as jet streams and storm tracks, could result in shifts in precipitation patterns affecting natural ecosystems, agriculture, and water resources. The implications of the expansion for stratospheric circulation and the distribution of ozone in the atmosphere are as yet poorly understood. The observed recent rate of expansion is greater than climate model projections of expansion over the twenty-first century, which suggests that there is still much to be learned about this aspect of global climate change.”

As mentioned earlier, the authors do not know whether the expansion of the tropics is a temporary (cyclic) occurrence that may go away sometime in the future or a more permanent change to the planet. They plan further meteorological studies, hoping to eventually learn the exact mechanisms—whether they are natural, artificial, or a combination of the two—that cause such expansion.

Possibly explanation of the expansion include rising surface temperatures of the oceans, ozone depletion in the stratosphere, periodic El Niño Southern Oscillation (ENSO) system, and climate changes within the stratosphere.


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