Warming Expands World's Tropics By 2+ Degrees Latitude In Just 25 Years - SMH

[hatrack]

GLOBAL warming has caused the world's tropical regions to expand much more rapidly than predicted, raising the prospect of an even drier farm belt in southern Australia, and the spread south of diseases such as dengue fever.

As talks on climate change begin at a United Nations meeting in Bali today, research reveals the tropical zone has widened by more than two degrees of latitude over the past 25 years. This is greater than the expansion expected by the end of this century, a study led by Dian Seidel, of the US National Oceanic and Atmospheric Administration, has revealed.

Dr Seidel said the surprisingly rapid expansion of the tropics could lead to "profound changes in the global climate system". Of greatest concern were shifts in rain and wind patterns that would affect natural ecosystems, agriculture and water resources in the world's subtropical dry belts, including southern Australia.

The director of the Research Institute for Climate Change and Sustainability at the University of Adelaide, Barry Brook, said it would push the westerly systems that bring rain to Australia's southern coast closer to the South Pole. "As they shift southwards, progressively more rain is dumped over the Southern Ocean, instead of over continental Australia, where we need it," he said. The expanding tropics would also extend the range of tropical diseases, Professor Brook said.

EDIT

http://www.smh.com.au/news/environment/greenhouse-robs-rainfall-in-farm-belt/2007/12/02/1196530481803.html

[mikelgb]

1. that's like 138 miles, damn...

[chaplainM]

2. You lost me

How does global warming change the tilt of the Earth's axis?

[GliderGuider]

3. Try thinking of it like this

The region of the Earth defined as tropical spreads out north and south of the Equator. The northern and southern boundaries of that region have been determined to have shifted away from the equator by 2 degrees of latitude. Because the earth is warming, the isothermal lines that define the boundary of the tropics have moved as a result. The zone defined as tropical has therefore expanded a bit.

I would guess that by the same token the Earth's polar zones have probably expanded a bit as well - possibly even more than the tropics because warming is more pronounced at the poles than at the equator.

No change to the tilt of the Earth's axis is needed.

[chaplainM]

4. Two definitions of "tropic?"

I get the part about the isothermals expanding, but IIRC, the tropics are the Northern and Southern latitudes at which the Sun's rays strike the Earth at 90 degrees at the summer and winter solstices, respectively.

[phantom power]

5. Yes, they are referring to a climate definition,

as opposed to an astronomical definition. So the climate zone defined as tropical is now larger, extending farther north, due to warming.

[chaplainM]

6. Thanks!

I can always count on DUers!