Category Archives: glaciers

On the Arctic sea ice

Sea ice extent in the Northern Hemisphere has exhibited large and anomalous declining trends over the last several decades. In particular, there has been over a 20% decline since 1979. Linear trends in arctic sea-ice extent since 1979 are negative in every month.Recently, there has been particular interest recently over a record-breaking year in 2007 which flew by the second-lowest year in 2005. There also has been a foot-race this year, which has kept me particularly interested over the last few weeks. For a while, it seemed that 2008 would clearly not surpass 2007, but due to the drop over the last few weeks, that may not be the case (although it probably will be). Sea ice extent as of September 7, 2008 is 4,739,844 km2, while 2007 minima reached 4,267,656 km2 on September 16th last year.

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More on glaciers Pt 1- Intro to glaciology

Roughly 10% of the land area on Earth is covered by glaciers– most of this number comes from the Antarctic and Greenland ice sheets. Other areas of permanent ice are scattered around in places like the Rockies, Alps, Andes, Himalayas, etc. Ice also covers roughly 7% of the oceans in the annual mean, though both hemispheres experience sea ice loss in their respective summers, and regrowth in their winters. Around 75% of the freshwater on Earth is stored in glaciers, and they provide water for millions of people worldwide. Glaciers form when more snow falls each year than can melt or evaporate. The snow piles up, is squeezed into ice under the weight of more snow (with an intermediate form called ‘firn’), and begins to flow under gravity. Such conditions are generally a function of both temperature and precipitation and are dominant at low latitudes and high altitudes, or high latitudes.

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A glacier perspective

The following images were presented by Dr. Lonnie Thompson at the latest AGU conference in California, in a powerpoint presentation. Just gives a bit of a persective on what is going on around the world. Ice is one of the first reactors to a climate change, and the pictures show that we are in a new climate. The images are from different parts of the world: the Himalays in Tibet, to the Andes in South America, Alaska, Glacier National Park, Italy, Africa, etc

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