If a tree falls in the forest, and no one is around to hear it, does climate change?

If a tree falls in the forest, and no one is around to hear it, does climate change?

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

In a review paper appearing in this week's Forest Ecology special issue of Science, atmospheric scientist Gordon Bonan of the Natinoal Science Foundation's National Center for Atmospheric Research in Boulder, Colo., presents the current state of understanding for how forests impact global climate.

 Forests cover nearly a third of the Earth's landmass. Falling into three categories -- tropical, temperate and boreal -- the forest types each have differing influences on local, regional and global climate.
Forests cover nearly a third of the Earth's landmass. Falling into three categories -- tropical, temperate and boreal -- the forest types each have differing influences on local, regional and global climate. (Photo Credit: Nicolle Rager Fuller, National Science Foundation)

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

 There are roughly 42 million square kilometers of forest on Earth, a swath that covers almost a third of the land surface, and those wooded environments play a key role in both mitigating and enhancing global warming.
There are roughly 42 million square kilometers of forest on Earth, a swath that covers almost a third of the land surface, and those wooded environments play a key role in both mitigating and enhancing global warming. (Photo Credit: Nicolle Rager Fuller, National Science Foundation)

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 and subtract from the equations that dictate the warming of the planet.

"In the Amazon, tropical rainforests remove carbon dioxide from the atmosphere," said 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.

 Forests play an integral role in the Earth's climate, and 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 the greenhouse gas carbon dioxide through photosynthesis and 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 currently an area that scientists are intensely studying.
Forests play an integral role in the Earth's climate, and 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 the greenhouse gas carbon dioxide through photosynthesis and 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 currently an area that scientists are intensely studying. (Photo Credit: Nicolle Rager Fuller, National Science Foundation)

As studies have explored the mechanisms behind these effects, and the effects themselves, researchers have come to recognize that calculating the specific harm from a specific local impact is a highly complicated problem.

"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," said Bonan. "Then we can begin to identify and understand the potential of forests to mitigate global warming."

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