Earth’s tropical zone “is expanding”

Climate change is rapidly expanding the size of the earth's tropical zone, threatening to bring disease and drought to heavily populated areas, Agence France-Presse reported, citing an Australian study. Researchers concluded that the tropics had widened by up to 500 kilometres in the past 25 years. The zone now extends well beyond the band circling the planet between the Tropic of Cancer and the Tropic of Capricorn.

Examining 70 peer-reviewed scientific articles, scientists at James Cook University looked at findings from long-term satellite measurements, weather-balloon data, climate models and sea-temperature studies to determine how global warming was impacting on the tropical zone.

Cook professor Steve Turton said the expansion of the tropical zone beyond its traditional definition meant the subtropical arid zone that borders the tropics was being pushed into temperate areas, with potentially devastating consequences. Severe drying is predicted.

“Such areas include heavily populated regions of southern Australia, southern Africa, the southern Europe-Mediterranean-Middle East region, the south-western United States, northern Mexico and southern South America,” Turton said. “If the dry subtropics expand into these regions,” he added, “the consequences could be devastating for water resources, natural ecosystems and agriculture, with potentially cascading environmental, social and health implications.”

Tropical diseases such as dengue fever were likely to become more prevalent, Turton noted, with some scientific models predicting that “the greatest increase in the annual epidemic potential of dengue will be into the subtropical regions”. They include the southern United States, China, northern Africa, South America, southern Africa, and most of Australia.

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