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The Greening of the Earth: 1982-1999
Young, S.S. and Harris, R. 2005. Changing patterns of global-scale vegetation photosynthesis, 1982-1999. International Journal of Remote Sensing 26: 4537-4563.

What was done
The authors analyzed, for the majority of earth's land surface, a near 20-year time series (1982-1999) of a vegetation indicator - the Normalized Difference Vegetation Index (NDVI) - calculated from data obtained from the Advanced Very High Resolution Radiometer (AVHRR) carried aboard U.S. National Oceanic and Atmospheric Administration satellites. In doing so, they employed two different datasets derived from the sensor: the Pathfinder AVHRR Land (PAL) data set and the Global Inventory Modeling and Mapping Studies (GIMMS) dataset.

What was learned
Based on their analysis of the PAL data, Young and Harris determined that "globally more than 30% of land pixels increased in annual average NDVI greater than 4% and more than 16% persistently increased greater than 4%," while "during the same period less than 2% of land pixels declined in NDVI and less than 1% persistently declined." With respect to the GIMMS dataset, the two scientists report that "even more areas were found to be persistently increasing (greater than 20%) and persistently decreasing (more than 3%)." All in all, they say that "between 1982 and 1999 the general trend of vegetation change throughout the world has been one of increasing photosynthesis."

As for what has been responsible for the worldwide increase in photosynthesis - which is the ultimate food source of nearly all of the biosphere - the researchers mention global warming (yes, it's a very good thing), as well as "associated precipitation change and increases in atmospheric carbon dioxide," citing Myneni et al. (1997) and Ichii et al. (2002). In addition, they say that "many of the areas of decreasing NDVI are the result of human activity," primarily deforestation (Skole and Tucker, 1993; Steininger et al., 2001) and urbanization Seto et al. (2000).

What it means
As the air's CO2 content continues to rise, the biosphere should become ever more productive and the earth should get greener and greener (if we do not destroy great parcels of it), not only in spite of rising temperatures and precipitation, but often because of them.

Ichii, K., Kawabata, A. and Yamaguchi, Y. 2002. Global correlation analysis for NDVI and climatic variables and NDVI trends: 1982-1990. International Journal of Remote Sensing 23: 3873-3878.

Myneni, R.C., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386: 698-702.

Seto, K.C., Kaufman, R.K. and Woodcock, C.E. 2000. Landsat reveals China's farmland reserves, but they're vanishing fast. Nature 406: 121.

Skole, D. and Tucker, C.J. 1993. Tropical deforestation and habitat fragmentation in the Amazon: satellite data from 1978 to 1988. Science 260: 1905-1909.

Steininger, M.K., Tucker, C.J., Ersts, P., Killen, T.J., Villegas, Z. and Hecht, S.B. 2001. Clearance and fragmentation of tropical deciduous forest in the Tierras Bajas, Santa Cruz, Bolivia. Conservation Biology 15: 856-866.

Reviewed 26 April 2006