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The Greening of the Earth Continues
Volume 5, Number 45: 6 November 2002

Carbon is the basic building block of life - at least as we know it - and it becomes so when CO2 is withdrawn from the atmosphere by photosynthesizing plants that use it to construct their tissues.  Because of this fact, and because literally thousands of laboratory and field experiments have demonstrated that the more CO2 there is in the air the better plants grow and the more efficiently they utilize water, it has been postulated that continued anthropogenic CO2 emissions will lead to a significant "greening of the earth" (Idso, 1986).  This suggestion constitutes a great hypothesis, because the inadvertent experiment humanity is currently conducting - our flooding of the air with CO2 as a result of burning prodigious quantities of fossil fuels - will ultimately demonstrate the truth of the hypothesis or expose its fallacy.

What's happened so far?

Perhaps the most comprehensive exposition of the status of the unplanned experiment was provided by Idso (1995), who cited a wealth of evidence for the validity of the greening hypothesis.  First, he described the ubiquitous range expansions of earth's woody plants that began approximately two centuries ago, when the air's CO2 content began to rise in response to the gathering steam of the Industrial Revolution.  Second, he described how the growth rates of many forests around the world increased concurrently, and how the most recent decades of fastest-rising atmospheric CO2 concentrations exhibited the greatest growth-rate enhancements.  Third, he described how the amplitude of the seasonal oscillation of the atmosphere's CO2 concentration - which is driven primarily by the photosynthetic and respiratory activities of the terrestrial biota - had risen hand in hand with the air's CO2 content over the prior thirty-five years of precise measurements of this phenomenon.

More recently, Zhou et al. (2001) used satellite measurements to demonstrate how vegetative activity increased by slightly over 8% and 12% between 1981 and 1999 in North America and Eurasia, respectively; while Ahlbeck (2002) employed statistical procedures to demonstrate that the primary driver of this phenomenon was the concurrent rise in the air's CO2 content, with regional warming playing a secondary role.  When some controversy arose over this conclusion (Kaufmann et al., 2002), we confirmed Ahlbeck's assessment of the situation by means of a quantitative comparison of what was observed via satellite and what would have been expected on the basis of the known strength of the aerial fertilization effect of the increase in atmospheric CO2 concentration that occurred over the period in question (see our Editorial of 18 September 2002).

Perhaps the most up-to-date information on the greening of the earth was made public in a brief article by Fred Pearce that was posted on the web site of New Scientist magazine on 16 September 2002.  Entitled "Africa's deserts are in 'spectacular' retreat," it tells the story of vegetation reclaiming great tracts of barren land across the entire southern edge of the Sahara.  This information may come as a bit of a surprise to many, especially since the United Nations Environment Program told the World Summit on Sustainable Development in Johannesburg, South Africa in August of this year (2002) that over 45% of the continent is currently experiencing severe desertification.  As is often the case with the environmental pronouncements of that great world body, however, the world of nature tells a vastly different story.

Pearce begins his article by reporting "the southern Saharan desert is in retreat, making farming viable again in what were some of the most arid parts of Africa," noting that "Burkina Faso, one of the West African countries devastated by drought and advancing deserts 20 years ago, is growing so much greener that families who fled to wetter coastal regions are starting to go home."

And the good news is not confined to Burkina Faso.  "Vegetation," according to Pearce, "is ousting sand across a swathe of land stretching from Mauritania on the shores of the Atlantic to Eritrea 6000 kilometers away on the Red Sea coast."  What is more, besides being widespread in space, the greening is widespread in time, having been happening since at least the mid-1980s.

Quoting Chris Reij of the Free University of Amsterdam, Pearce says "aerial photographs taken in June show 'quite spectacular regeneration of vegetation' in northern Burkina Faso."  The data indicate the presence of more trees for firewood and more grassland for livestock.  In addition, a survey that Reij is collating shows, according to Pearce, "a 70 percent increase in yields of local cereals such as sorghum and millet in one province in recent years."  Also studying the area has been Kjeld Rasmussen of the University of Copenhagen, who reports that since the 1980s there has been a "steady reduction in bare ground" with "vegetation cover, including bushes and trees, on the increase on the dunes."

Pearce also reports on the work of a team of geographers from Britain, Sweden and Denmark that spent much of the past summer analyzing archived satellite images of the Sahel.  Citing Andrew Warren of University College London as a source of information on this unpublished study, he says the results show "that 'vegetation seems to have increased significantly' in the past 15 years, with major regrowth in southern Mauritania, northern Burkina Faso, north-western Niger, central Chad, much of Sudan and parts of Eritrea."

Do these findings take us by surprise?  Not in the least.  Fully twenty years ago, Idso (1982) declared that if the ongoing rise in the air's CO2 content were allowed to continue unabated, thereby enhancing plant growth and improving vegetative water use efficiency, "semi-arid lands not now suitable for cultivation could be brought into profitable production; and with added water available for irrigation, the deserts themselves could 'blossom as the rose'."

Also, in our Editorial of 15 March 1999, we reported that in a study of a series of satellite images of the Central and Western Sahel that were taken from 1980 to 1995, Nicholson et al. (1998) could find no evidence of any overall expansion of deserts and no drop in the rainfall use efficiency (similar to water use efficiency) of native vegetation.  And we further reported that in a satellite study of the entire Sahel from 1982 to 1990, Prince et al. (1998) actually detected a steady rise in rainfall use efficiency, suggesting that plant productivity and coverage of the desert had increased during this period.

Yes, in spite of drought and everything else - natural or otherwise - that may have combined to frustrate biospheric productivity throughout the course of the Industrial Revolution and beyond, the greening of the earth continues ... courtesy of the aerial fertilization effect and the water conservation effect of the ongoing rise in the air's CO2 content.

Sherwood, Keith and Craig Idso

Ahlbeck, J.R.  2002.  Comment on "Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999" by L. Zhou et alJournal of Geophysical Research 107: 10.1029/2001389.

Idso, S.B.  1982.  Carbon Dioxide: Friend or Foe?  IBR Press, Tempe, Arizona, USA.

Idso, S.B.  1986.  Industrial age leading to the greening of the Earth?  Nature 320: 22.

Idso, S.B.  1995.  CO2 and the Biosphere: The Incredible Legacy of the Industrial Revolution.  Department of Soil, Water & Climate, University of Minnesota, St. Paul, MN.

Kaufmann, R.K., Zhou, L., Tucker, C.J., Slayback, D., Shabanov, N.V. and Myneni, R.B.  2002.  Reply to Comment on "Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999" by J.R. Ahlbeck.  Journal of Geophysical Research 107: 10.1029/1001JD001516.

Nicholson, S.E., Tucker, C.J. and Ba, M.B.  1998.  Desertification, drought, and surface vegetation: An example from the West African Sahel.  Bulletin of the American Meteorological Society 79: 815-829.

Prince, S.D., Brown De Colstoun, E. and Kravitz, L.L.  1998.  Evidence from rain-use efficiencies does not indicate extensive Sahelian desertification.  Global Change Biology 4: 359-374.

Zhou, L., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V. and Myneni, R.B.  2001.  Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999.  Journal of Geophysical Research 106: 20,069-20,083.