New scientific research shows that the tropical region has moved towards the poles at a faster rate than had been predicted, writes Kristen Hallam.
Earth's tropical region, as defined by rain and wind patterns, expanded north and south over the past few decades, another sign of global climate change, researchers reported today. The tropics have moved towards the poles at a faster rate than existing models of climate change have predicted, the scientists wrote in the journal Nature Geoscience. That may broaden the area affected by hurricanes and change precipitation patterns in subtropical regions, the researchers said.
Early signs of global warming include melting ice and thawed land in the Arctic region, and the study also suggests the tropics are changing in response to rising temperatures. An ongoing expansion would shift the sub-tropical zones, encompassing the Mediterranean region, the southwestern US, Mexico, southern Australia, South Africa and parts of South America, they said.
"A poleward expansion of the tropics is likely to bring even drier conditions to those heavily populated regions, but may bring increased moisture to other areas," scientists led by Dian Seidel of the National Oceanic and Atmospheric Administration Air Resources Library in Silver Spring, Maryland, wrote in the journal.
The UN Intergovernmental Panel on Climate Change said in a report in February that the probability that humans are causing global warming is 90 per cent, and world temperatures and sea levels will increase by the end of the century. Delegates from about 190 nations will meet tomorrow on the Indonesian island of Bali to begin two weeks of talks over a successor to the Kyoto Protocol, an international treaty to slow global warming through limits on greenhouse gas emissions, which expires in 2012.
To astronomers and mapmakers, the tropics are bordered by the Tropics of Cancer and Capricorn, which fall at about 23.5 degrees north and south of the equator. Climatologists tend to measure the area differently, using changes in atmospheric temperatures, winds and ozone observations. Ms Seidel's team of climatologists reviewed recent research on the width of the tropical belt.
They found that the tropics had expanded north and south by about 2.5 degrees in latitude over the past 25 years. Under the most extreme climate change model, the tropics were forecast to move 2 degrees by the end of this century, the researchers said. The findings suggest better models may be needed, and further research into the regional and seasonal characteristics of the widening tropics should be explored in detail, the scientists wrote. - (Bloomberg)