Planet Earth

The outermost layer of the atmosphere will lose 3 percent of its density over the coming decade. (Credit: NCAR)
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Recent observations by scientists tracking satellite orbits have shown that the thermosphere, which begins about 60 miles above Earth and extends up to 400 miles, is beginning to become less dense, said Robert Kerr, program director in the National Science Foundation's (NSF) Division of Atmospheric Sciences.

At heights of more than 60 miles, one of the main elements of the atmosphere is atomic oxygen, a single atom of oxygen. As carbon dioxide increases near Earth's surface, it gradually diffuses upward and absorbs heat through collisions with atomic oxygen. It then radiates the heat away to space through infrared radiation, and the result is a net cooling of the upper atmosphere. As the molecules cool and settle, the thermosphere loses density.

Also affecting the thermosphere is the 11-year cycle of solar activity. During the active phase of the cycle, ultraviolet light and energetic particles from the sun increase, producing a warming and expansion of the upper atmosphere. When solar activity wanes, the thermosphere settles and cools.

Read more Science Daily releases 12 December 2006
Original Source: National Science Foundation Press Release


By about 2040, the Arctic may be nearly devoid of sea ice during the late summer unless greenhouse gas emissions are significantly curtailed. (Illustration copyright UCAR)
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Arctic sea ice has retreated in recent years, especially in the late summer, when ice thickness and area are at a minimum. To analyze how global warming will affect the ice in coming decades, the team studied a series of seven simulations run on the NCAR-based Community Climate System Model, one of the world's leading tools for studying climate change. The scientists first tested the model by simulating fluctuations in ice cover since 1870, including a significant shrinkage of late-summer ice from 1979 to 2005. The simulations closely matched observations, a sign that the model was accurately capturing the present-day climate variability in the Arctic.

The research team points to several reasons for the abrupt loss of ice in a gradually warming world. Open water absorbs more sunlight than does ice, meaning that the growing regions of ice-free water will accelerate the warming trend. In addition, global climate change is expected to influence ocean circulations and drive warmer ocean currents into the Arctic.

"As the ice retreats, the ocean transports more heat to the Arctic and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice," Holland explains. "This is a positive feedback loop with dramatic implications for the entire Arctic region."

Read more Science Daily releases 12 December 2006
Original Source: The National centre for Atmospheric Research


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Climate experts search for answers in the oceans
By absorbing half of the carbon dioxide emitted into the atmosphere, the oceans have a profound influence on climate. However, their ability to take up this carbon dioxide might be impaired as a result of climate change. To determine their response to global warming, ESA has backed two projects that provide systematic data on key oceanic variables – colour and temperature.

Read more ESA News 11th December 2006
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