Changing frontiers

The planet Earth is divided into three climate zones: Tropical, temperate and frigid. The tropical zone extends around the equator from 23.5 degrees north to 23.5 degrees south. Now researchers say that this warm temperature zone is expanding further and this may be the reason behind severe droughts and bushfires in Australia and parts of the U.S. What is causing this expansion? Studies have suggested that increasing greenhouse gases, aerosols, and decreasing ozone may be the factors behind this expansion. A new study recently published in the Journal of Geophysical Research: Atmospheres notes that warming oceans are the main reason. “Our model calculations show that large-scale ocean currents in both the northern and southern hemispheres are the key drivers,” says Hu Yang, lead author of the study in a release from Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research.

“Because the currents in this region bring the water masses together particularly strongly, the subtropical ocean surface accumulates heat more easily here than in other marine regions - just like with plastic," explains Gerrit Lohmann, one of the authors in the release. “So far, people have assumed complex changes in the atmosphere to be the cause. In truth, it is a relatively simple mechanism for ocean currents.”