It goes on to say that no one knows what the tipping point is in terms of how much is too much. Posted in today's World Energy Watch at Buzzflash.com
http://news.mongabay.com/2007/0725-pnas.htmlHumans appropriate 24% of Earth's productivity
Human landscapes occupy 35% of the planet's ice-free land surface
mongabay.com
July 25, 2007
Researchers have developed the first geographically detailed analysis of humankind's impact on the biosphere, as represented by a metric known as HANPP or human appropriation of net primary production. The results are presented and discussed in two papers published in the July 6 online edition of the journal Proceedings of the National Academy of Sciences.
Using vegetation modeling, agricultural and forestry statistics, and geographical information systems data on land use, land cover, and soil degradation that localizes human impact on ecosystems, a team lead by Helmut Haber of Austria's Klagenfurt University show that humans are presently appropriating 23.8% of potential net primary productivity -- 15.6 pentagram of carbon per year. Of this amount, 53 percent of appropriation results from harvest, 40% from land-use-induced productivity changes, and 7% from human-induced fires. The work shows that humans are having a massive impact on Earth's resources.
"Our research has documented that Humans are indeed becoming a force in changing the global environment," David Zaks, a research assistant at the University of Wisconsin - Madison's Center for Sustainability & the Global Environment (SAGE), told mongabay.com. "The importance of these studies lies in reframing previously benign numbers into a story that more effectively portrays our collective actions on the planet."
The researchers present a series of maps that show how humans are appropriating the planet's resources. Zaks says that in most areas background productivity has decreased due to human activities, though in some areas it has been artificially increased through intensive fertilization, irrigation and mechanization of agriculture. The researchers add that intensification is a matter of necessity, resulting from shrinking opportunities for expansion -- croplands and pastures now rival forests as the largest ecosystems on the planet, occupying 35 percent of the ice-free land surface. The rise of such human dominated landscapes has come at the expense of natural ecosystems.
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