[Texgreen] Humans have lowered the surface of the earth by 6 cm!

[Roger Baker]

<http://environment.newscientist.com/channel/earth/mg19225824.600- 
people-the-most-powerful-earthmovers-of-all.html>


People, the most powerful earth-movers of all

16 December 2006

IT WOULD be equivalent to lowering the surface of the Earth by 6
centimetres. That's how much soil humankind has so far eroded. At the
height of the Roman empire, people started moving more earth than all
natural forces combined, while today, erosion from agriculture alone
moves more sediment - about 21 gigatons per year -than continental
glaciers managed at their peak during the Pleistocene Ice Age.

Geologists at Syracuse University in New York and the University of
Texas at Austin calculated the natural rate of sediment erosion and
deposition over the past 500 million years from previously published
studies. They then compared this background rate of erosion to the
current global rate, extrapolated from the amount of erosion taking
place in agricultural areas in the US. The modern rate of cropland
erosion is 10 to 15 times as high as the background geologic rate, the
researchers found (Geological Society of America Bulletin, DOI:
10.1130/B25899.1).

Despite the scale of human-induced erosion, team member Brandon
McElroy at the University of Texas notes that the overall impact is
relatively small in terms of Earth history. He also believes the main
threat to feeding the world's population in the future will not be the
continued loss of soil by erosion, but further population increases.

 From issue 2582 of New Scientist magazine, 16 December 2006, page 17