photosynthetically active radiation: UNH Global Land Remote SensingPoor farmers in Asia, Africa and South America face a double threat: climate change and loss of soil fertility, Alexander Muller of the Food and Agricultural Organization warned 3 years ago.
Food security hangs by a thread: with drought in Africa and China; millions displaced by earthquakes and the 2004 Asian tsunami; the 2008 food shortage, triggered by biofuel speculation, which caused riots in 38 countries. Under-financed like other UN agencies, the FAO has been unable to find permanent solutions for either problem: disaster refugees or the hungry poor.
New satellite-sensing data show that worldwide land fertility has fallen steadily for 20 years, affecting 24% of the earth's cropland and forests -- shockingly higher and in different regions than the 15% estimate by soil experts in the previous GLASOD (Global Assessment of Soil Degradation – see map). The new 20 Mar 2009 report by Bai et al. from Wageningen University warns that unless halted, the loss in NPP (net primary productivity) in these regions – previously productive tropical countries with a quarter of world population – will become an additional driver of global warming.
This loss in ecosystem services is alarming. The Wageningen authors say vegetation loss meant a thousand million tonnes of CO2 was not captured. At a shadow price of $50 per tonne, that is $50 billion. That might be doubled by the unestimated loss of organic carbon already fixed in the soil.
Challenging the usual interpretation of causes, the new study finds only “weak correlations” with traditional culprits: rural population density and drought. Among likely causes are
- industrial: the hamburger connection in Central America, Brazil, now spreading to Africa; other man-made destruction of tropical forests; monoculture, topsoil erosion, forcing crops with irrigation and artificial fertilizers, chemical pollution, and urban sprawl.
- traditional agriculture: overgrazing, deep ploughing, absence of fallow, cutting of fuelwood.
The study shows that the fastest degradation is not in regions already identified by GLASOD as undergoing desertification or erosion, the African Sahel and around the Mediterranean. The worst-affected countries are
- Africa, the Congo, Zaire, Equatorial Guinea, Gabon, Sierra Leone, Zambia, Asia, Myanmar, Malaysia, Thailand, Laos, Korea and Indonesia, with over 50% of land area degraded
- Swaziland with 95 per cent land area degraded
- rural China (nearly half a billion people), India, Indonesia, Bangladesh and Brazil.
See FAO country-by-country GLASOD maps; Wageningen's GlobalSoilMap.net; UNEP Earthwatch; AfSIS; Saba Ganguly's critique of India's green revolution, the most successful; NASA's illustrated explanation of remote sensing and the NDVI vegetation index; the new AgCam which begins operation this year; Encyclopedia of Earth's article on the great transition.