Beetle-Killed Rocky Mountain Forest Could Affect Local Weather, Air Quality As Well As Climate - AFP

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For example, some tiny airborne particles from plants rise into clouds and seed them, providing a surface for water droplets to adhere to and develop into raindrops. Greenhouse gases such as carbon dioxide (CO2), which is emitted in large quantities from beetle-devastated forests, combine with extra CO2 produced by human activities to influence the amount of heat from the Sun that reaches Earth or gets reflected back into space. Plants also emit chemicals known as volatile organic compounds that can interact with human-caused pollution to influence the formation of particles and ground-level ozone, or smog, affecting both air quality and local temperatures.

When large areas of trees are killed by pine beetles or other causes, these interactions are disrupted. This may change cloud and precipitation patterns for a decade or more, which can, in turn, further alter the land cover.

Preliminary computer modeling suggests that beetle kill can lead to temporary temperature increases of about 2-4 degrees Fahrenheit. This is partly because of a lack of foliage to reflect the Sun's heat back into space. Scientists also believe that beetle kill stimulates trees to release more particles and chemicals into the atmosphere as they try to fight off the insects. This worsens air quality, at least initially, by increasing levels of ground-level ozone and particulate matter.

Wildfires, clear-cutting, and new development also affect the atmosphere by removing vegetation. But the impacts in each case can vary significantly, depending on the remaining vegetation and changes to soil conditions. The exchange of gases and particles between the surface and the atmosphere is critical in arid areas such as the western United States. Even slight changes in precipitation can have significant impacts on the region. "Here in the western United States, it is particularly important to understand these subtle impacts on precipitation," Guenther says. "Rain and snow may become even more scarce in the future as the climate changes, and the growing population wants ever more water."

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http://www.terradaily.com/reports/On_Rocky_Mountain_Beetle_Kill_Could_Impact_Regional_Air_Quality_999.html