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Humans 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.



Map of the human appropriation of net primary production (HANPP), excluding human-induced fires. Total HANPP as a percentage of NPP0. Blue (negative values) indicates increases of NPPact (a) or NPPt (b) over NPP0, green and yellow indicate low HANPP, and red to dark colors indicate medium to high HANPP. Image copyright PNAS / Haber et. al (2007).


"The rise of modern agriculture and forestry has been one of the most transformative events in human history," write the authors of the discussion paper. "Whether by clearing natural ecosystems or by intensifying practices on existing croplands, pastures, and forests, human land-use activities are consuming an ever-larger share of the planet's biological productivity and dramatically altering the Earth's ecosystems in the process."

Led by University of Wisconsin professor Jonathan A. Foley, the authors of the discussion paper conclude by questioning how long the trend can continue.

"Given the magnitude of these effects, it is natural to ask how our use of terrestrial ecosystems can be sustained, let alone be expanded, as we consider the potential for future population growth, continued economic development (and associated changes in diet), and increasing interest in biologically based energy sources. Will the future growth of human land use come at the expense of continued ecological degradation (7) or rely on the unsustainable crutches of fossil fuels and fossil water?" the authors ask. "Ultimately, we need to question how much of the biosphere's productivity we can appropriate before planetary systems begin to break down. 30%? 40%? 50%? More? Or have we already crossed that threshold?"

CITATION: Helmut Haber, K. Heinz Erb, Fridolin Krausmann, Veronika Gaube, Alberte Bondeau, Christoph Plutzar, Simone Gingrich, Wolfgang Lucht, and Marina Fischer-Kowalski (2007). Quantifying and mapping the human appropriation of net primary production in earth's terrestrial ecosystems PNAS published July 6, 2007, 10.1073/pnas.0704243104

Jonathan A. Foley, Chad Monfreda, Navin Ramankutty, and David Zaks (2007). Our share of the planetary pie. PNAS published July 31, 2007, 10.1073/pnas.0705190104 12585—12586

Related

Amazon deforestation damaging critical ecosystem services. Human disturbance of the Amazon rainforest is more extensive than previously thought say a team of scientists writing in the current edition of the journal Frontiers in Ecology. Reviewing recent research on the Amazon ecosystem, they note that human activities are affecting the health of the forest and impacting the ecological goods and services the Amazon provides mankind.

New maps reveal the human footprint on Earth. As global populations swell, farmers are cultivating more and more land in a desperate bid to keep pace with the ever-intensifying needs of humans. As a result, agricultural activity now dominates more than a third of the Earth's landscape and has emerged as one of the central forces of global environmental change, say scientists at the Center for Sustainability and the Global Environment (SAGE) at UW-Madison.



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