'Tropics expand' as world warms

Submitted by Charles Frost on Sun, 12/09/2007 - 08:18.

'Tropics expand' as world warms


Climate change is causing the tropics to widen, with possible impacts on the global food supply, research suggests.


Scientists examined five different measures of the width of the tropical belt, and found it expanded by between 2 and 4.8 degrees latitude since 1979.


Other researchers meanwhile said climatic change could increase the number of thunderstorms in the


The findings emerged as delegates met in
Bali for UN climate talks focusing on reducing greenhouse gas emissions.


The capacity of poorer countries - many of them in the tropics - to respond and adapt to impacts of climate change will be another major theme of the talks.


Widening belts


The new analysis of tropical expansion comes from a team of US scientists who reviewed five separate strands of evidence, all gathered from satellite data.


While geographers define "The Tropics" rigidly as the region between 23.5 degrees North and 23.5 degrees South, to atmospheric scientists it is a more variable zone marked by features such as the jet stream and the circulation known as Hadley cells.



On these measures, the tropics have expanded since the era of reliable satellite observation began in 1979.


"The edges of the tropical belt are the outer boundaries of the subtropical dry zones, and their poleward shift could lead to fundamental shifts in ecosystems and in human settlements," the researchers write in the journal Nature Geoscience.


"Shifts in precipitation patterns would have obvious implications for agriculture and water resources, and could present serious hardships in marginal areas."


The Intergovernmental Panel on Climate Change (IPCC) warned in its series of reports this year that serious impacts on food and water supplies lie ahead, including:


  • 75-250 million people across
    Africa could face water shortages by 2020


  • Crop yields could increase by 20% in East and South East Asia, but decrease by up to 30% in Central and
    South Asia


  • Agriculture fed by rainfall could drop by 50% in some African countries by 2020


The scientists behind the new study note that the tropical zone appears to be expanding much faster than predicted by computer models.


Thunder rolls


While impacts on agriculture could prove important for developing countries, a bigger concern for richer nations such as the
US may be the damage wrought by extreme weather.


The IPCC forecasts stronger hurricanes in the future, but possibly fewer of them. Now another
US team is suggesting an increase in thunderstorms over the country as well.


In the journal Proceedings of the National Academy of Sciences (PNAS), researchers report a computer modelling study that projects a doubling of the frequency of weather conditions right for the formation of severe thunderstorms.


Already, they write, extreme weather events are costing the
US economy more than $2bn (£970m) each year.


From: http://news.bbc.co.uk/2/hi/science/nature/7126069.stm

Tropics Migrating Northward, Hastening Spread of Diseases

Tropics Migrating Northward, Hastening Spread of Tropical Diseases


by Jeremy Elton Jacquot, Los Angeles on 12. 7.07

A trend that has already helped accelerate the spread of certain infectious diseases - the northward movement of tropical regions - could become much worse as global warming continues to intensify. In a recently published article in the journal Nature Geoscience, Dian Seidel of NOAA and her colleagues write about signs they observed in the stratosphere that indicate that tropical climate patterns may have expanded by up to 4.5° of latitude in the Northern hemisphere over the past 25 years.

This movement is much more dramatic than the one predicted by prior climate models, which had suggested an expansion of 2° of latitude north and south - within the next century. To discover this worrying trend, Seidel and her fellow researchers studied five sets of data from 1979 to 2000 containing information about tropical climate pattern indicators, such as ozone concentrations and temperatures. Both were seen to increase, suggesting an expanding tropical belt.

Seidel attributes the large discrepancy between her study's predictions and those made by other climate models to the impact of the stratosphere, which doesn't tend to be well represented in models. Aside from subjecting subtropical and temperate ecosystems to tremendous pressure, Seidel is worried about the unpredictable effects the migrating tropical belt will have on the spread of vectors, such as mosquitoes, and infectious diseases.

Via ::Science: Tropics on the Move (news website), ::National Geographic News: Climate Change Pushing Tropics Farther, Faster (news website)

See also: ::Planting Trees Helps Fight Global Warming, but Only in the Tropics, ::New Worries about Climate Change-Induced Spread of Infectious Diseases

From: http://www.treehugger.com/files/2007/12/tropics_migrating.php