Climate |
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The climate is the weather averaged over a long period of time. Weather is the combination of events in the atmosphere and climate is the overall accumulated weather in a certain location. Over historic time spans there are a number of static variables that determine climate, including: latitude, altitude, proportion of land to water, and proximity to oceans and mountains.
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Other climate determinants are more dynamic: The thermohaline circulation of the ocean distributes heat energy between the equatorial and polar regions; other ocean currents do the same between land and water on a more regional scale. Degree of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level.
Alterations in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming or global cooling. The variables which determine climate are numerous and the interactions complex, but there is general agreement that the broad outlines are understood, at least in so far as the determinants of historical climate change are concerned..
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Antarctic ice sheet |
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The Antarctic ice sheet is the largest single mass of ice on Earth.It covers an area of almost 14 million square km and contains 30 million cubic km of ice. Around 90 percent of the fresh water on the Earth's surface is held in the ice sheet,an amount equivalent to 70 m of water in the world's oceans. In East Antarctica, the ice sheet rests on a major land mass, |
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an amount equivalent to 70 m of water in the world's oceans. In East Antarctica, the ice sheet rests on a major land mass, but in West Antarctica the bed can extend to more than 2500m below sea level. The land would be seabed if the ice sheet were not there. Ice enters the sheet through snow and frost and leaves by calving of icebergs and melting, usually at the base but also sometimes at the surface at warm sites..
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Arctic warming fast |
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Though there are significant variations across the region, on average the Arctic is warming twice as fast as the rest of the planet, according to a major report released last year. |
Further warming for Arctic
The Arctic Climate Impact Assessment, a four-year study involving hundreds of scientists, projected an additional temperature rise of 4-7C by 2100. If the current trend can be ascribed in part to human-induced climate change, Mark Serreze sees major reasons for concern. "What we're seeing is a process in which we start to lose ice cover during the summer," he said, "so areas which formerly had ice are now open water, which is dark.
"These dark areas absorb a lot of the Sun's energy, much more than the ice; and what happens then is that the oceans start to warm up, and it becomes very difficult for ice to form during the following autumn and winter. "It looks like this is exactly what we're seeing - a positive feedback effect, a 'tipping-point'."
The idea behind tipping-points is that at some stage the rate of global warming would accelerate, as rising temperatures break down natural restraints or trigger environmental changes which release further amounts of greenhouse gases.
Possible tipping-points include the disappearance of sea ice leading to greater absorption of solar radiation a switch from forests being net absorbers of carbon dioxide to net producers melting permafrost, releasing trapped methane This study is the latest to indicate that such positive feedback mechanisms may be in operation, though definitive proof of their influence on the Earth's climatic future remains elusive.
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| Partly Sunny |
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| 31°C |
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| Humidity: 40% |
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