In a new study, scientists have shown how the tropics have widened due to human environmental effects.

Previous studies have shown that the width of the tropical belt has been increasing since at least the late 1970s, based on a variety of indicators.

Jian Lu, and his team at the National Center for Atmospheric Research, Boulder, Colorado, US, use one such indicator to show that the observed widening of the tropics can be accurately replicated by an atmospheric general circulation model forced by the observed evolution since 1958 of global sea surface temperatures and sea ice distributions along with the direct radiative effects from natural and human-generated sources.

The indicator is the frequent occurrence at high altitudes of the boundary between the troposphere and the stratosphere (tropopause).

The researchers then contrasted this simulation with one forced only by sea surface temperatures and sea ice distributions and found that the widening trend of the tropics can be attributed entirely to direct radiative forcing, in particular those related to greenhouse gases and stratospheric ozone depletion.

In fact, modifying sea surface temperatures actually causes no significant change in the width of the tropics and in some simulated seasons leads to a tropical belt contraction. (ANI)