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Global Greening Trends
Reference
Xiao, J. and Moody, A.  2005.  Geographical distribution of global greening trends and their climatic correlates: 1982-1998.  International Journal of Remote Sensing 26: 2371-2390.

What was done
Several research teams have reported an increase in global vegetative productivity over the latter portion of the 20th century (Kawabata et al., 2001; Ichii et al., 2002; Nemani et al., 2003; Cao et al., 2004), which has been attributed to a number of different factors, including nitrogen deposition, forest regrowth, wetter rainfall regimes, increased solar radiation reception, global warming, and the aerial fertilization effect of atmospheric CO2 enrichment.  In the present study, Xiao and Moody seek to shed further light on this phenomenon by analyzing trends in global vegetative activity from 1982 to 1998 using a recently developed satellite-based vegetation index (Version 3 Pathfinder NDVI) in conjunction with a gridded global climate dataset (global monthly mean temperature and precipitation at 0.5° resolution from New et al., 2000).

What was learned
Greening trends were found to exhibit substantial latitudinal and longitudinal variability.  The most intense greening of the globe was observed in high northern latitudes, portions of the tropics, southeastern North America and eastern China.  Temperature was found to correlate strongly with greening trends in Europe, eastern Eurasia and tropical Africa.  Precipitation, on the other hand, was not found to be a significant driver of increases in greenness, except for isolated and spatially fragmented regions.  Some decreases in greenness were also observed, mainly in the Southern Hemisphere in southern Africa, southern South America and central Australia, which trends were associated with concomitant increases in temperature and decreases in precipitation.  There were also large regions of the globe that showed no trend in greenness over the 17-year period, as well as large areas that are undergoing strong greening trends that showed no association with trends of either temperature or precipitation.  These greening trends, the authors conclude, must be the result of other factors, such as "CO2 fertilization, reforestation, forest regrowth, woody plant proliferation and trends in agricultural practices."

What it means
In spite of all the dire phenomena that the world's climate alarmists claim have had a detrimental impact on the biosphere over the last two decades of the 20th century (two of the warmest decades in the instrumental temperature record, three intense and persistent El Niņos, the eruption of Mt. Pinatubo, illicit logging, fires, storms, etc.), vast areas of the globe actually experienced increases in vegetative productivity over that period, due to simultaneous and overpowering good things that occurred, like rising air temperatures and increasing atmospheric CO2 concentrations, both of which typically are demonized by those who pay far more attention to the virtual world of climate models than to what is known about physiological responses of plants to these important environmental factors.

References
Cao, M., Prince, S.D., Small, J. and Goetz, S.J.  2004.  Remotely sensed interannual variations and trends in terrestrial net primary productivity 1981-2000.  Ecosystems 7: 233-242.

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.

Kawabata, A., Ichii, K. and Yamaguchi, Y.  2001.  Global monitoring of international changes in vegetation activities using NDVI and its relationship to temperature and precipitation.  International Journal of Remote Sensing 22: 1377-1382.

Nemani, R.R., Keeling, C.D., Hashimoto, H., Jolly, W.M., Piper, S.C., Tucker, C.J., Myneni, R.B. and Running. S.W.  2003.  Climate-driven increases in global terrestrial net primary production from 1982 to 1999.  Science 300: 1560-1563.

New, M., Hulme, M. and Jones, P.D.  2000.  Global monthly climatology for the twentieth century (New et al.).  Dataset.  Available online (http://www.daac.ornl.gov) from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, USA.

Reviewed 9 November 2005