How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

The Inexorable Greening of Earth's Arid Lands
Volume 6, Number 21: 21 May 2003

Over two decades ago, when the atmosphere's CO2 concentration was approximately 340 ppm (up from a pre-industrial value on the order of 280 ppm), Idso (1982) stated in a small self-published book (Carbon Dioxide: Friend or Foe?) that if the air's CO2 content continued to climb, it would ultimately enhance plant growth and water use efficiency to the point that semi-arid lands not then suitable for cultivation "could be brought into profitable production," further stating that "the deserts themselves could 'blossom as the rose'."  A few years later he advanced essentially the same thesis, this time in the pages of Nature (Idso, 1986) in a brief paper entitled "Industrial Age Leading to the Greening of the Earth."

Throughout most of the succeeding years, this optimistic view of the ongoing rise in the air's CO2 content -- and the great good it can do for humanity and nature alike -- was largely ignored, as the world's climate alarmists took center stage with headline-grabbing predictions of catastrophic CO2-induced global warming.  Now, however, it appears that enough has finally been learned to take this upbeat idea more seriously, in support of which statement we note the following titles of recent science stories that have appeared in the popular press.

"Greenhouse Gas Might Green Up the Desert" declares a recent ScienceDaily headline.  "Missing Carbon Dioxide Greens Up the Desert" chimes in the Israel National News.  "Greenhouse Gas Soaked Up by Forests Expanding into Deserts" proclaims The Independent.  And in a grudging acknowledgement of the hard-to-ignore good news, the World News reports that "Deserts Bloom in Bad Air."

What is the source of this recent spate of basically positive stories?  It is the scientific paper of Grunzweig et al. (2003) that was published in the pages of Global Change Biology, wherein the authors tell the tale of the Yatir forest -- a 2800-hectare stand of primarily Aleppo pine (Pinus halepensis Mill.) containing smaller amounts of Cupressus sempervirens and other pine trees (mostly P. brutia) -- which was planted some 35 years ago at the edge of the Negev Desert in Israel.

An intriguing aspect of this particular forest -- which Grunzweig et al. characterize as growing in poor soil of only 0.2 to 1.0 meter's depth above chalk and limestone -- is that although it is located in an arid region that receives less annual precipitation than all of the other scores of FluxNet stations in the global network of micrometeorological tower sites that use eddy covariance methods to measure exchanges of CO2, water vapor and energy between terrestrial ecosystems and the atmosphere (Baldocchi et al., 2001), its annual net ecosystem CO2 exchange (NEE) is just as high as that of many high-latitude boreal forests and actually higher than that of most temperate forests.

How can this possibly be?  Grunzweig et al. note that the increase in atmospheric CO2 concentration that has occurred since pre-industrial times should have improved water use efficiency [WUE] in most plants by increasing the ratio of CO2 fixed to water lost via evapotranspiration.  That this hypothesis is indeed correct has been demonstrated under controlled experimental conditions by Leavitt et al. (2003) within the context of the still-ongoing long-term atmospheric CO2 enrichment study being conducted by Idso and Kimball (2001) on sour orange (Citrus aurantium L.) trees.  It has also been confirmed in nature by Feng (1999), who obtained identical CO2-induced WUE responses for 23 groups of naturally-occurring trees (scattered across western North America) that were caused by the rise in the air's CO2 content that occurred between 1800 and 1985.

Feng concludes that this phenomenon "would have caused natural trees in arid environments to grow more rapidly, acting as a carbon sink for anthropogenic CO2," which is exactly what Grunzweig et al. have demonstrated to be happening in the Yatir forest on the edge of the Negev Desert.  In addition, the latter authors report that "reducing water loss in arid regions improves soil moisture conditions, decreases water stress and extends water availability," which "can indirectly increase carbon sequestration by influencing plant distribution, survival and expansion into water-limited environments."  Hence, they conclude that "expanding afforestation efforts into drier regions may be significant for carbon sequestration and associated benefits (restoration of degraded land, reducing runoff, erosion and soil compaction, improving wildlife) because of the large spatial scale of the regions potentially involved (ca. 2 x 109 hectares of global shrub-land and C4 grassland)."

That this phenomenon is indeed widespread is born out by the recent study of Eklundh and Olsson (2003), who analyzed Normalized Difference Vegetation Index (NDVI) data from the NOAA Advanced Very High Resolution Radiometer (AVHRR) that were obtained over the African Sahel for the period 1982-2000.  As they describe their findings, "strong positive change in NDVI occurred in about 22% of the area, and weak positive change in 60% of the area," while "weak negative change occurred in 17% of the area, and strong negative change in 0.6% of the area."  They also report that "integrated NDVI has increased by about 80% in the areas with strong positive change," while in areas with weak negative change, "integrated NDVI has decreased on average by 13%."

The primary story told by these data is one of strong positive trends in NDVI for large areas of the African Sahel over the last two decades of the 20th century; and Eklundh and Olsson conclude that the "increased vegetation, as suggested by the observed NDVI trend, could be part of the proposed tropical sink of carbon."

In conclusion, we note that as ever more data from various parts of the world are obtained and analyzed [see Greening of the Earth (Summary) in our Subject Index], it is becoming ever more clear that the CO2-induced "reverse desertification" theory of Idso (1982, 1986) is receiving ever more support in the way of real-world observations.

Keith and Craig Idso

Baldocchi, D., Falge, E., Gu, L.H., Olson, R., Hollinger, D., Running, S., Anthoni, P., Bernhofer, C., Davis, K., Evans, R., Fuentes, J., Goldstein, A., Katul, G., Law B., Lee, X.H., Malhi, Y., Meyers, T., Munger, W., Oechel, W., Paw U, K.T., Pilegaard, K., Schmid, H.P., Valentini, R., Verma, S., Vesala, T., Wilson, K. and Wofsy, S.  2001.  FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities.  Bulletin of the American Meteorological Society 82: 2415-2434.

Eklundh, L. and Olssson, L.  2003.  Vegetation index trends for the African Sahel 1982-1999.  Geophysical Research Letters 30: 10.1029/2002GL016772.

Feng, X.  1999.  Trends in intrinsic water-use efficiency of natural trees for the past 100-200 years: A response to atmospheric CO2 concentration.  Geochimica et Cosmochimica Acta 63: 1891-1903.

Grunzweig, J.M., Lin, T., Rotenberg, E., Schwartz, A. and Yakir, D.  2003.  Carbon sequestration in arid-land forest.  Global Change Biology 9: 791-799.

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. and Kimball, B.A.  2001.  CO2 enrichment of sour orange trees: 13 years and counting.  Environmental and Experimental Botany 46: 147-153.

Leavitt, S.W., Idso, S.B., Kimball, B.A., Burns, J.M., Sinha, A. and Stott, L.  2003.  The effect of long-term atmospheric CO2 enrichment on the intrinsic water-use efficiency of sour orange trees.  Chemosphere 50: 217-222.