快猫短视频

MOST of the world鈥檚 glaciers are shrinking, according to a new satellite
survey of over 2000 of them.

Anecdotal evidence already suggests that glaciers on Mount Kilimanjaro in
Tanzania and in Glacier National Park in Montana are shrinking
(快猫短视频, 13 May 2000, p 28).
Now infrared and visible photographs taken
by the Japanese instrument ASTER on board NASA鈥檚 Terra spacecraft show that
glaciers all over the globe are melting.

ASTER takes about two days to map the surface of the Earth with a resolution
of about 90 metres. Better still, it can zoom in on interesting sites to
resolutions as fine as 15 metres.

Rick Wessels of the US Geological Survey in Flagstaff, Arizona, compared
thousands of ASTER images with aerial photographs taken up to 20 years ago. He
found that almost every mountain glacier in Patagonia, the Himalayas, the Alps
and the Pyrenees had shrunk by hundreds of metres, and some by several
kilometres. 鈥淪ome glaciers are more like snowbanks,鈥� he told the AGU.

Wessels also looked at images of mountain lakes at the base of melting
glaciers. Many have grown over the past 10 years and show up as dark blue
instead of light blue, indicating higher levels of sediments. This suggests that
they are melting more quickly and that the meltwater is eroding the hills.

ASTER鈥檚 three telescopes take pictures at three wavelengths, two infrared and
one visible, to differentiate snow, ice and debris-covered ice. 鈥淭he images have
better than half a degree accuracy in temperature,鈥� says Kurt Thome of the
University of Arizona.