To obtain a broad perspective on this question, Indermuhle et al. (1999) determined the age and composition of air bubbles trapped in glacial ice cores retrieved from Taylor Dome, Antarctica, which allowed them to reconstruct a history of carbon exchanges among the atmosphere, oceans and land biota over the past 11,000 years.  This effort indicated that the atmosphere's CO2 concentration at approximately 10,500 years before present (yr BP) was 268 ppm, that it fell to a value of 260 ppm at about 8,200 yr BP, and that it increased monotonically and "almost linearly" from that point in time to a value of 285 ppm 7,000 years later (about 1,200 yr BP).  Model calculations based on carbon isotope data further revealed that the drawdown of atmospheric CO2 from 10,500 to 8,200 yr BP was consistent with terrestrial vegetative regrowth and soil build-up on areas previously covered by ice sheets, "as well as a climatic development towards the mid-Holocene optimum."  Thereafter, however, the scientists' work revealed a gradual loss of terrestrial carbon over the next 7,000 years, which they say was likely "due to a change from the warmer and wetter mid-Holocene climate to colder and drier conditions."

These observations convincingly demonstrate that the warm and moist mid-Holocene has not been called the Holocene Climatic Optimum for nothing.  Indeed, Indermuhle et al.'s work clearly shows that it was the premier period of terrestrial vegetative prowess of the present interglacial, and that earth's biosphere has been going steadily downhill ever since (or at least to the start of the Industrial Revolution).  Even the 25 ppm increase in the air's CO2 content from 8,200 to 1,200 yr BP was not enough to stem the downward biological spiral induced by the planet's slowly deteriorating climate.  Now, however, with an anthropogenically-induced rate of increase in atmospheric CO2 concentration that is fully two orders of magnitude greater, we can expect to see this situation reverse itself, as it has indeed been doing ever since the demise of the Little Ice Age.

Langenfelds et al. (1999) provided a good example of this phenomenon by analyzing O2/N2 measurements of the contents of a suite of tanks filled with background air collected at Cape Grim, Tasmania between April 1978 and January 1997, a period of time during which climate alarmists claim the earth experienced global warming of a magnitude "unprecedented" over the past two millennia (Mann and Jones, 2003).  The rates of carbon storage in the world's oceans and the terrestrial biosphere they derived from these data indicated the terrestrial biosphere was essentially in balance with respect to surface fluxes of carbon throughout this 19-year interval.  However, it is known from other studies that tropical deforestation produced a huge net loss of carbon during each of those years.  As a result, Langenfelds et al. were forced to acknowledge the existence of a terrestrial carbon sink of like magnitude.  This "compensating growth of the [terrestrial] biosphere," as they describe it, was suggested by them to be due to "reforestation, higher rates of net production in response to climatic trends, fertilisation by elevated levels of atmospheric CO2 or nitrogen deposition or a combination of these factors."  Thus, although the physician is often accused of failing to heal himself, the biosphere appears to be doing just fine in this regard, yearly re-sequestering all of the carbon that man takes out of it.

Using a totally different technique (satellite observations of vegetative activity), Nemani et al. (2003) also discovered a terrestrial biosphere growing ever more robust.  Globally, the group of eight scientists determined that terrestrial net primary production (NPP) increased by 6.17%, or 3.42 PgC, over the 18 years between 1982 and 1999.  What is more, they observed net positive responses over all latitude bands studied: 4.2% (47.5-22.5°S), 7.4% (22.5°S-22.5°N), 3.7% (22.5-47.5°N), and 6.6% (47.5-90.0°N).

Nemani et al. mention a number of likely contributing factors to these significant NPP increases: nitrogen deposition and forest regrowth in northern mid and high latitudes, wetter rainfall regimes in water-limited regions of Australia, Africa, and the Indian subcontinent, increased solar radiation reception over radiation-limited parts of Western Europe and the equatorial tropics, warming in many parts of the world, and the aerial fertilization effect of rising atmospheric CO2 concentrations everywhere.

With respect to the latter factor, which is featured prominently on our website (see our Plant Growth Data section and fully half of all of our Journal Reviews), Nemani et al. remark that "an increase in NPP of only 0.2% per 1-ppm increase in CO2 could explain all of the estimated global NPP increase of 6.17% over 18 years and is within the range of experimental evidence [our italics]."  However, they report that NPP increased by more than 1% per year in Amazonia alone, noting that "this result cannot be explained solely by CO2 fertilization."

We tend to agree with them, but we additionally note that the aerial fertilization effect of atmospheric CO2 enrichment is most pronounced at higher temperatures (see the four sub-headings under Growth Response to CO2 with Other Variables - Temperature in our Subject Index), rising from next to nothing at a mean temperature of 10°C to a 0.33% NPP increase per 1-ppm increase in CO2 at a mean temperature of 36°C for a mixture of plants comprised predominantly of herbaceous species (Idso and Idso, 1994).  For woody plants, we could possibly expect this number to be two (Idso, 1999) or even three (Saxe et al., 1998; Idso and Kimball, 2001; Leavitt et al., 2003) times larger, yielding a 0.7% to 1% NPP increase per 1-ppm increase in CO2, which would indeed represent the lion's share of the growth stimulation observed by Nemani et al. in tropical Amazonia.

Be that as it may, the all-important take-home message of Nemani et al.'s study is that satellite-derived observations reveal the planet's terrestrial biosphere to have significantly increased its productivity over the last two decades of the 20th century in the face of a host of both real and imagined environmental stresses.  But what of the future?

Using a process-based ecosystem model, Xiao et al. (1998) made monthly calculations of carbon and nitrogen fluxes and their pool sizes in various terrestrial ecosystems to compute global net ecosystem production (NEP) from 1990 to 2100 based on three different scenarios of atmospheric CO2 and temperature change.  For the scenario with lower-than-typically-assumed increases in CO2 emissions and air temperature, the NEP of the globe increased from a positive (carbon-sequestering) value of 0.8 Pg C yr^-1 in 1990 to 1.3 Pg C yr^-1 in 2100, for a rate increase of 62% over the 110-year period.  For typically-assumed increases in CO2 and temperature, corresponding NEP values were 0.8 and 2.6 Pg C yr^-1, yielding a rate increase of 225%.  And for higher-than-typically-assumed increases in CO2 and temperature, NEP values of 0.8 and 3.4 Pg C yr^-1 were obtained, for a rate increase of 325%.

What would such dramatic increases in NEP do for the planet's animal life?  In a unique approach to this question, Kaspari et al. (2000) studied 49 ground ant assemblages, including two from South America, six from Central America, and 41 from North America.  With site net primary productivity (NPP) varying over three orders of magnitude and ant abundance varying over two orders of magnitude, they found that ant abundance rose with increasing site NPP, and that NPP alone accounted for 56% of the variation in ant abundance, with the next best predictor explaining only 8% of the variation.

Now ants are ectotherms; and ectotherms represent most of the world's animal biomass and biodiversity (Wilson, 1993).  Consequently, as Kaspari et al. state, "understanding the mechanisms that regulate ectotherm abundance is key to predicting the impacts of climate change."  In this regard, they further note that "this study is the first we know of that explores factors regulating the abundance of a taxon over the terrestrial productivity gradient;" and what they found clearly demonstrates that a site's NPP is the primary determinant of ectotherm abundance.  Consequently, based on the fact that atmospheric CO2 enrichment invariably leads to increases in ecosystem NPP, we can confidently state that the ongoing rise in the air's CO2 content should prove to be extremely beneficial for the vast majority of earth's animal life in terms of promoting both abundance and diversity.

An intriguing indication that these CO2- and temperature-induced biological benefits are indeed in process of occurring in the real world of nature comes from the decline in the air's diurnal temperature range (DTR) that is evident in many parts of the world (Easterling et al., 1997).  By way of explanation, Collatz et al. (2000) employed a simple land surface subroutine in a general circulation model of the atmosphere that included parameterizations of canopy physiological responses to various environmental changes; and by running the model with and without the vegetation subroutine, they were able to determine the degree of influence that the planet's plant life may have on near-surface air temperature in a world of rising temperature and atmospheric CO2 concentration.

In this regard, it was determined that realistic changes in the amount and physiological activity of earth's plant life can produce changes in DTR of the order observed in the real world.  In addition, the authors explicitly state that their results "suggest that reported increases in vegetation cover in the Northern Hemisphere during the 1980s [Myneni et al., 1997] could have contributed to the lowered DTR."  Hence, whereas it has long been believed that the declining diurnal temperature range near the surface of the earth is a "fingerprint" of deleterious CO2-induced global warming, it now appears that the declining DTR may be an indication of beneficial CO2-induced "global greening," which by virtue its observation - as per Myneni et al. (1997) - is known to be helping both natural and agro-ecosystems become more productive.

So much for the "twin evils" of warming and atmospheric CO2 enrichment.  They appear to be just what the plant doctor ordered to rejuvenate an under-performing terrestrial biosphere.

References
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Easterling, D.R., Horton, B., Jones, P.D., Peterson, T.C., Karl, T.R., Parker, D.E., Salinger, M.J., Razuvayev, V., Plummer, N., Jamason, P. and Folland, C.K.  1997.  Maximum and minimum temperature trends for the globe.  Science 277: 364-367.

Idso, K.E. and Idso, S.B.  1994.  Plant responses to atmospheric CO2 enrichment in the face of environmental constraints: a review of the past 10 year's research.  Agricultural and Forest Meteorology 69: 153-203.

Idso, S.B.  1999.  The long-term response of trees to atmospheric CO2 enrichment.  Global Change Biology 5: 493-495.

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.

Indermuhle, A., Stocker, T.F., Joos, F., Fischer, H., Smith, H.J., Wahlen, M., Deck, B., Mastroianni, D., Tschumi, J., Blunier, T., Meyer, R. and Stauffer, B.  1999.  Holocene carbon-cycle dynamics based on CO2 trapped in ice at Taylor Dome, Antarctica.  Nature 398: 121-126.

Kaspari, M., Alonso, L. and O'Donnell, S.  2000.  Three energy variables predict ant abundance at a geographical scale.  Proceedings of the Royal Society of London Series B 267: 485-489.

Langenfelds, R.L. Francey, R.J. and Steele, L.P.  1999.  Partitioning of the global fossil CO2 sink using a 19-year trend in atmospheric O2.  Geophysical Research Letters 26: 1897-1900.

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.

Mann, M.E. and Jones, P.D.  2003.  Global surface temperatures over the past two millennia.  Geophysical Research Letters 30: 10.1029/2003GL017814.

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.

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.

Saxe, H., Ellsworth, D.S. and Heath, J.  1998.  Tree and forest functioning in an enriched CO2 atmosphere.  New Phytologist 139: 395-436.

Wilson, E.O.  1993.  The Diversity of Life.  W.W. Norton & Co., New York, NY.

Xiao, X., Melillo, J.M., Kicklighter, D.W., McGuire, A.D., Prinn, R.G., Wang, C., Stone, P.H. and Sokolov, A.  1998.  Transient climate change and net ecosystem production of the terrestrial biosphere.  Global Biogeochemical Cycles 12: 345-360.