Global warming pushing edges of tropics towards poles: study

Greenhouse effect is causing Earth’s zone of tropical climate to creep towards the poles, according to a study whose release on Sunday...

Greenhouse effect is causing Earth’s zone of tropical climate to creep towards the poles, according to a study whose release on Sunday coincided with the eve of a major UN conference on climate change.

The poleward expansion of the tropics will have far-reaching impacts, notably in intensifying water scarcity in the Mediterranean and the US “Sun belt” as well as southern Africa and southern Australia, it warns.

The paper, appearing in a new journal Nature Geoscience, is an overview of the latest published research into atmospheric systems at the tropics. For cartographers, the tropical belt is defined by the tropics of Cancer and Capricorn, at latitudes 23.5 degrees north and south of the equator.

For climatologists, though, where the tropics end is fuzzier because of the complexity of a powerful high-altitude wind pattern, known as the Hadley circulation.

Some years ago, the first credible computer simulations predicted that, as the Earth warmed, the Hadley jet streams and their associated wind and rainfall patterns would move poleward.

Under the most extreme scenario, the tropics were on average predicted to expand by about two degrees latitude, equivalent to around 200 km over the 21st century.