TROPICAL RAINFORESTS: Disappearing Opportunities
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Rainforest canopy in the late afternoon. (Photo by R. Butler)

GLOBAL CONSEQUENCES

Tropical rainforests play a vital role in the functioning of the planet's natural systems. The forests regulate local and global weather through their absorption and creation of rainfall and their exchange of atmospheric gases. For example, the Amazon alone creates 50-80 percent of its own rainfall through transpiration. Cutting the rainforests changes the reflectivity of the earth's surface, which affects global weather by altering wind and ocean current patterns, and changes rainfall distribution. If the forests continue to be destroyed, global weather patterns may become more unstable and extreme.



CLIMATIC ROLE OF FORESTS

As previously discussed, tropical rainforests play a vital role in local climate regulation by their interaction with water cycles. However, rainforests also have a significant effect on global weather. Rainforests, like all forms of vegetation, affect the "surface albedo" or reflectivity of a surface by absorbing more heat than bare soil. Norman Myers (1997) explains,
    Much of the energy that converts surface moisture into water vapor comes from the sun's radiational heating of the land surface. The energy thus depends on surface albedo, or relevant degree of reflectant "shininess" of the land surface (Gash and Shuttleworth 1992). In turn, the albedo depends on the vegetation, which absorbs more heat than does bare soil. Over thick vegetation, vigorous thermal currents take moisture (provided by the same plant cover) up into the atmosphere, where it condenses as rain. Because of its influence on convection patterns and wind currents, and hence on rainfall regimes, the albedo effect constitutes a basic factor in controlling climate.
The loss of forest vegetative cover means less heat absorption translating to less moisture being taken up into the atmosphere.

Rainfall is also affected when forest-clearing fires create air pollution and release tiny particles, known as aerosols, into the atmosphere. While aerosols can both heat and cool the air, depending on their size, shape, and color, high concentrations of biomass-burning aerosols directly impact local climate by increasing cloud formation but decreasing rainfall, according to research by NASA. In areas with lots of smoke, "cloud droplets form around the aerosol particles, but may never grow large enough to fall as rain," say researchers with NASA's Goddard Space Flight Center who studied the effect. Thus large forest fires have the effect of further reducing rainfall, leaving burned areas more prone to dryness and future fires.

In the long run, these changes explain why deforested regions may experience a decline in rainfall.

Tropical deforestation can also affect weather in other parts of the world. A 2005 study by NASA found that deforestation in the Amazon region of South America influences rainfall from Mexico to Texas and in the Gulf of Mexico, while forest loss in Central Africa affects precipitation patterns in the upper and lower U.S Midwest. Similarly, deforestation in Southeast Asia was found to impact rainfall in China and the Balkan Peninsula.

Soybeans may worsen drought in the Amazon rainforest
Expansion of agriculture in the Amazon may impact climate
Amazon drought extends into second year
Will Amazon drought worsen in 2007?
Changes in forest cover could significantly affect climate
Temperate forests may worsen global warming


Review questions:
  • Why does local rainfall decline with deforestation?

[print version | spanish | french | chinese | japanese]


Continued: Atmospheric Role of Forests





Unless otherwise specified, this article was written by Rhett A. Butler [Bibliographic citation for this page]


Other pages in this section:
Consequences of Deforestation
Erosion
Loss of Renewable Resources
Atmospheric Role
- - - - -
References
References
References
References
References
Local Climate Regulation
Loss of Species, Disease
Climactic Role
Extinction
- - - - -
Kids version of this section
- Why are rainforests important?
- Climate
- Home to wildlife
- Water cycle
- Erosion control
- Extinction




Recent news

Prince Charles calls for rainforest protection to fight climate change
(5/15/2008) Ending the destruction of tropical rainforests is the simplest step to helping address climate change, said Prince Charles in an interview with the BBC.

Nitrogen pollution harming ecosystems and contributing to global warming
(5/15/2008) Nitrogen pollution of the world's oceans is harming marine ecosystems and contributing to global warming, report two reviews published in the journal Science.

U.S. climate policy could help save rainforests
(5/14/2008) U.S. policy measures to fight global warming could help protect disappearing rainforests, says the founding partner of an "avoided deforestation" policy group. In an interview with mongabay.com, Jeff Horowitz of the Berkeley-based Avoided Deforestation Partners argues that U.S. policy initiatives could serve as a catalyst for the emergence and growth of a carbon credits market for forest conservation. REDD or Reducing Emissions from Deforestation and Degradation is a proposed policy mechanism that would compensate tropical countries for safeguarding their forests. Because deforestation accounts for around a fifth of global greenhouse gas emissions, efforts to reduce deforestation can help fight climate change. Forest protection also offers ancillary benefits like the preservation of ecosystem services, biodiversity, and a homeland for indigenous people.

NASA study links changes in Earth's systems to global warming
(5/14/2008) Human-induced climate change has impacted a wide range of Earth's natural systems, including permafrost, lakes, and oceans, reports a new study led by scientists from NASA's Goddard Institute for Space Science (GISS).

Al Gore's investment firm bets that rainforest conservation will be profitable
(5/14/2008) Al Gore's investment firm has signaled an interest in the emerging market for ecosystem services by taking an equity position in an innovative Australian financial company.


More news on climate change


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Copyright Rhett Butler 1994-2007

"Rainforest" is used interchangeably with "rain forest" on this site.
Same for "rainforests" and "rain forests". "Jungle" is generally not used.