From: David A Gabel, ENN
Published May 3, 2011 09:24 AM

Global Climate Change Affects Tropical as well as Polar Regions

The most often heard victims of climate change are the polar bears in the far north losing their hunting grounds to the melting polar ice. Maps show the greatest area of warming temperatures are at the north and south poles. However, equally important are the effects of climate change in the tropical regions of the world. As temperatures rise here, poorly adaptable species may be lost forever. It may also encourage the spread of diseases and unprecedented heat waves which may lead to forest fires.

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Studies of climate changes effects in the tropics have been conducted by William Laurance, Distinguished Research Professor at James Cook University in Queensland, Australia. His research has covered the entire world, from the Amazon to Africa, to tropical Australia. He notes prior research conducted by biologist, Justin Welbergen, who made observations on an Australian day where temperatures reached 42.9 degrees C (109 F). The extreme heat caused the deaths of 1,453 flying foxes along the northeastern Australian coastline. Since then, tens of thousands more have died. Prior to 1994, few mass die-offs were ever recorded.

Tropical species are perfectly suited for their climate. There are no seasons like in the northern latitudes, so these species have never experienced any serious deviations in temperature. In the tropics the only way to experience different temperatures is to change elevation. Generally, the temperature drops 6 degrees C (11 F) for every thousand meters up. Therefore, tropical species are also perfectly suited for their elevation.

This means trouble for mountaintop species because they are effectively on an island and have nowhere else to go. As temperatures rise, these high elevation species will be the first in danger. Laurance's colleague, Steve Williams, has created a model which suggests that extinctions will increase if temperatures rise more than three degrees. If they rise by 5-6 degrees, most endemic life in north Queensland will be exterminated.

Another concern for the tropics is global warming's effects on cloud cover in tropical mountain regions. The rainforests in these areas depend on persistent cloud cover to keep them cool and protect them from solar radiation. Rising temperatures can change the condensation point for cloud formation, drying out these areas. It will also affect the evapotranspiration of plants. Rainforest plants release massive amounts of water vapor when they absorb CO2. But in a CO2-rich world, plants do not have to release water vapor to absorb CO2. The reduction in water vapor released will result in fewer or smaller clouds.

There are still many uncertainties when predicting climate change in the tropics. Will there be more floods or droughts in a warming world? The El-Nino weather phenomenon may cause droughts in the Amazon, but will this be the dominant climate dynamic for the region? Will undisturbed rainforests grow or shrink due to rising temperatures? We simply do not know the answers to many of these questions. The hope is that tropical ecosystems will find the resilience to withstand the rapid warming that is unleashed on them.

For more information: http://e360.yale.edu/feature/the_worlds_tropical_forests_are_already_feeling_the_heat/2397/

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