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Forests and Climate Change: What's Their Role in Global Warming?

There are roughly 16 million square miles of forest on Earth (or 42 million square kilometers), a swath that covers almost a third of the land surface. Those wooded environments play a key role in both mitigating and enhancing the strength of global warming.

NCAR researcher Gordon Bonan reviewed the current state of understanding of how forests affect global climate for a special issue of Science on Forest Ecology that hit newstands on June 12, 2008.

"As politicians and the general public become more aware of climate change, there will be greater interest in legislative policies to mitigate global warming," says Bonan. "Forests have been proposed as a possible solution, so it is imperative that we understand fully how forests influence climate."

The teeming life of forests, and the physical structures containing them, are in continuous flux with incoming solar energy, the atmosphere, the water cycle and the carbon cycle—in addition to the influences of human activities. The complex relationships both add to and subtract from the equations that dictate the warming of the planet.

"In the Amazon, tropical rainforests remove carbon dioxide from the atmosphere," says Bonan. "This helps mitigate global warming by lowering greenhouse gas concentrations in the atmosphere. These forests also pump moisture into the atmosphere through evapotranspiration. This cools climate and also helps to mitigate global warming."

While even the earliest European settlers in North America recognized that the downing of forests affected local climates, the global impact of such activities has been uncovered over more recent decades as new methods, analytical tools, satellites, and computer models have revealed the global harm that forest devastation can cause.

Calculating the specific harm from a specific local impact is a highly complicated problem involving the mechanisms behind these effects, and the effects themselves.

"We need better understanding of the many influences of forests on climate, both positive and negative feedbacks, and how these will change as climate changes," says Bonan. "Then we can begin to identify and understand the potential of forests to mitigate global warming."


Learn More


still frame from video interview with NCAR scientist Gordon Bonan

video icon Webcast: Forests and Climate Change. NSF's Josh Chamot talks with NCAR scientist Gordon Bonan about how forests affect climate. Bonan discusses how forests can both cool and, in some cases, warm our planet and describes efforts to better understand the complicated feedbacks between forests and climate. Click here or on the image to open an NSF page where the webcast can be launched. (Video courtesy National Science Foundation/National Center for Atmospheric Research.)

illustration of variations in the effects on climate of three different types of forest

Forests play an integral role in Earth's climate. Each forest type—tropical, temperate and boreal—has varying impacts on the climate, serving to both cool and warm the Earth. Forests help reduce global warming by absorbing an important greenhouse gas, carbon dioxide, through photosynthesis and by cooling the atmosphere through evaporation and transpiration. However, some forests, such as boreal forests in the northern latitudes, can be darker than their surrounding terrain and absorb the Sun's energy more readily, which can lead to increasing warming. The play between these competing influences is an area that scientists are intensely studying. [ENLARGE] (Illustration by Nicolle Rager Fuller, National Science Foundation.)

global map with distribution of 3 types of forest

Nearly a third of Earth's landmass is forested. Different species of vegetation have adapted to conditions near the equator (tropical), mid-way between the equator and the poles (temperate), and closest to the poles (boreal, also called taiga). Each forest type has differing influences on local, regional and global climate. [ENLARGE] (Illustration by Nicolle Rager Fuller, National Science Foundation.)
• by Joshua A. Chamot
National Science Foundation

Spring-Summer 2008
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation.


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