A Service of The Greening Earth Society   

Green Alert

December 31, 2001 Vol. 1, No. 14

Biological sequestration of carbon long has been considered by climate change activists as a potential way to slow the rate at which the atmosphere’s carbon dioxide (CO2) concentration rises. Fear of possibly catastrophic changes in climate suggested by computer simulations of what happens once the CO2 concentration doubles caused carbon sequestration to be incorporated into climate treaty negotiations. If one accepts the validity of the computer model-generated global warming scenarios produced by the Intergovernmental Panel on Climate Change, some such strategy seems warranted. The problem with this way of thinking, however, is the notion that the concentration will double unless something new is done. But, as noted by Wofsy (2001), the rate of CO2 accumulation in the atmosphere over the past two decades already "has stayed the same or even declined slightly," in spite of the fact that emissions of CO2 from the combustion of fossil fuels have increased almost 40 percent over the same time period.

Wofsy entitled his article, "Where has all the carbon gone?" If humans are not removing it from the air, something else must be. That something only can be a natural process of biological carbon sequestration. Earth’s vegetation already has, automatically, risen to the challenge (or opportunity) and grown ever more vigorously in response to the aerial fertilization effect of atmospheric CO2 enrichment. This biological response is the greening of planet earth.

While some contend this makes for a nice story and admit the concept does have solid experimental backing, they ask if there is any real-world evidence that it truly is occurring where it really counts – in nature. Data from a number of meticulous scientific studies suggest that it is.

In a 1994 paper published in Science, Phillips and Gentry report results from tree biomass assessments at forty of the world’s tropical forests. They demonstrated that these highly productive ecosystems have become even more productive, at least since 1960. They became still more productive after 1980. This phenomenon – because of its "consistency and simultaneity of the changes on several continents" – is attributed to "enhanced productivity induced by increased CO2" (Pimm and Sugden, 1994).

Four years later, Phillips et al. (1998) likewise published a paper in Science describing results from similar measurements made "at fifty sites scattered throughout the Amazon and Central America … of more than a hundred thousand trees over the past thirty years." They also see an ongoing acceleration of tree growth. At the time, they calculated that it was large enough to account for approximately 40 percent of the so-called missing carbon of the entire globe! In fact, Laurance (1999) concludes, "In the Amazon basin alone, intact rainforests could be absorbing over one billion tons of carbon dioxide each year."

If we fast-forward to the present, we find a news item published on the National Geographic Society’s website on December 13, 2001. Entitled "Adult Amazon Trees Gain Mass, Puzzle Scientists," the article reports how a scientific team – again headed by Phillips – marvels at the increasing growth rates of large trees in the Amazon over the past two decades. They describe their finding as "unexpected." This is because "mature forests were thought to be ‘carbon neutral,’ giving off as much carbon as they absorb each day." As a consequence the scientists now contend, "The increased mass of Amazonian forests suggests they are acting as a huge ‘carbon sink,’ absorbing more carbon from the atmosphere than they release." Phillips also suggests, "The Amazon forests have become more massive as a result of increased amounts of carbon dioxide in the atmosphere."

But what about the northern boreal forests? In a paper published September 16, 2001, in the Journal of Geophysical Research, Zhou et al. report changes in a satellite-sensed parameter called the normalized difference vegetation index (NDVI) for the period July 1981 to December 1999. What did they find? Much of the vegetated area between 40° and 70° N latitude in Eurasia shows "a persistent increase in growing season NDVI over a broad contiguous swath of land from central Europe through Siberia to the Aldan plateau, where almost 58% is forests and woodlands." They also note increases in season-long NDVI in forests of the southeastern United States. Over the two-decade period they studied, the NDVI data – which the authors say "are surrogates of plant photosynthetic activity" – increased in magnitude by 12 percent in Eurasia and by eight percent in North America.

References

Laurance, W.F. 1999. Gaia's lungs: Are rainforests inhaling earth's excess carbon dioxide? Natural History (April), p. 96.

Phillips, O.L. and Gentry, A.H. 1994. Increasing turnover through time in tropical forests. Science 263: 954-958.

Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W.F., Nunez, P.V., Vasquez, R.M. Laurance, S.G., Ferreira, L.V., Stern, M., Brown, S. and Grace, J. 1998. Changes in the carbon balance of tropical forests: Evidence from long-term plots. Science 282: 439-442.

Pimm, S.L. and Sugden, A.M. 1994. Tropical diversity and global change. Science 263: 933-934.

Wofsy, S.C. 2001. Where has all the carbon gone? Science 292: 2261-2263.

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 to 1999. Journal of Geophysical Research 106: 20,069-20,083.

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This continues a series of "greening alerts" that Greening Earth Society periodically publishes online in response to research concerning the impact of carbon dioxide emissions on earth’s biosphere, especially as it relates to plant life’s ability to sequester carbon. The alerts are prepared by Drs. Sherwood B. Idso and Keith E. Idso of the Center for the Study of Carbon Dioxide and Global Change in Tempe, Arizona (www.co2science.org).