How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic

Feeding Humanity to Help Save Natural Ecosystems:
The Role of the Rising Atmospheric CO2 Concentration

Volume 5, Number 36: 4 September 2002

How much land can ten billion people spare for nature? This provocative question was posed by Waggoner (1995) in the title of an essay designed to illuminate the dynamic tension that exists between the need for land to support the agricultural enterprises that sustain mankind and the need for land to support the natural ecosystems that sustain all other creatures.  As noted by Huang et al. (2002), human populations "have encroached on almost all of the world's frontiers, leaving little new land that is cultivatable."  And in consequence of humanity's ongoing usurpation of this most basic of natural resources, Raven (2002) notes that "species-area relationships, taken worldwide in relation to habitat destruction, lead to projections of the loss of fully two-thirds of all species on earth by the end of this century."

If one were to pick the most significant problem currently facing the biosphere, this would probably be it: a single species of life, Homo sapiens, is on course to completely annihilate fully two-thirds of the ten million or so other species with which we share the planet within a mere hundred years, simply by taking their land.  Global warming, by comparison, pales in significance.  Its impact is nowhere near as severe, being possibly nil or even positive.  In addition, its root cause is highly debated; and actions to thwart it are much more difficult, if not impossible, to both define and implement.  Furthermore, what many people believe to be the cause of global warming, i.e., anthropogenic CO2 emissions, may actually be a powerful force for preserving land for nature.

What parts of the world are likely to be hardest hit by this human land-eating machine?  Tilman et al. (2001) note that developed countries are expected to actually withdraw large areas of land from farming over the next fifty years, leaving developing countries to shoulder essentially all of the growing burden of feeding our expanding species.  In addition, they calculate that the loss of these countries' natural ecosystems to cropland and pasture will amount to about half of all potentially suitable remaining land, which "could lead to the loss of about a third of remaining tropical and temperate forests, savannas, and grasslands," along with the many unique species they support.

What can be done to alleviate this bleak situation?  In a new analysis of the problem, Tilman et al. (2002) introduce a few more facts before suggesting some solutions.  They note, for example, that by 2050 the human population of the globe is projected to be 50% larger than it is today and that global grain demand could well double, due to expected increases in per capita real income and dietary shifts toward a higher proportion of meat.  Hence, they but state the obvious when they conclude that "raising yields on existing farmland is essential for 'saving land for nature'."

So how is it to be done?  Tilman et al. (2002) suggest a strategy that is built around three essential tasks: (1) increasing crop yield per unit of land area, (2) increasing crop yield per unit of nutrients applied, and (3) increasing crop yield per unit of water used.

With respect to the first of these requirements, Tilman et al. note that in many parts of the world the historical rate of increase in crop yields is declining, as the genetic ceiling for maximal yield potential is being approached.  This observation, they say, "highlights the need for efforts to steadily increase the yield potential ceiling."  With respect to the second requirement, they note that "without the use of synthetic fertilizers, world food production could not have increased at the rate it did [in the past] and more natural ecosystems would have been converted to agriculture."  Hence, they say the ultimate solution "will require significant increases in nutrient use efficiency, that is, in cereal production per unit of added nitrogen, phosphorus," and so forth.  Finally, with respect to the third requirement, Tilman et al. note that "water is regionally scarce," and that "many countries in a band from China through India and Pakistan, and the Middle East to North Africa either currently or will soon fail to have adequate water to maintain per capita food production from irrigated land."  Increasing crop water use efficiency, therefore, is also a must.

Although the impending biological crisis and several important elements of its potential solution are thus well defined, Tilman et al. (2001) report that "even the best available technologies, fully deployed, cannot prevent many of the forecasted problems."  This is also the conclusion of the study of Idso and Idso (2000), who - although acknowledging that "expected advances in agricultural technology and expertise will significantly increase the food production potential of many countries and regions" - note that these advances "will not increase production fast enough to meet the demands of the even faster-growing human population of the planet."

Fortunately, we have a powerful ally in the ongoing rise in the air's CO2 content that can provide what we can't.  Since atmospheric CO2 is the basic "food" of essentially all terrestrial plants, the more of it there is in the air, the bigger and better they grow.  For a nominal doubling of the air's CO2 concentration, for example, the productivity of earth's herbaceous plants rises by 30 to 50% (Kimball, 1983; Idso and Idso, 1994), while the productivity of its woody plants rises by 50 to 80% or more (Saxe et al. 1998; Idso and Kimball, 2001).  Hence, as the air's CO2 content continues to rise, so too will the land use efficiency of the planet rise right along with it (see also Plant Growth Data on our website).  In addition, atmospheric CO2 enrichment typically increases plant nutrient use efficiency and plant water use efficiency (see Nitrogen Use Efficiency and Water Use Efficiency in our Subject Index).  Thus, with respect to all three of the major needs noted by Tilman et al. (2002), increases in the air's CO2 content pay huge dividends, helping to increase agricultural output without the taking of new lands from nature.

In conclusion, it would appear that the extinction of two-thirds of all species of plants and animals on the face of the earth is essentially assured within the next century, if world agricultural output is not dramatically increased.  This unfathomable consequence will occur simply because we will need more land to produce what is required to sustain us and, in the absence of the needed productivity increase, because we will simply take that land from nature to keep ourselves alive.  It is also the conclusion of scientists who have studied this problem in depth that the needed increase in agricultural productivity is not possible, even with anticipated improvements in technology and expertise.  With the help of the ongoing rise in the air's CO2 content, however, Idso and Idso (2000) have shown that we should be able - but just barely - to meet our expanding food needs without bringing down the curtain on the world of nature.

That certain forces continue to resist this reality is truly incredible.  More CO2 means life for the planet; less CO2 means death ... and not just the death of individuals, but the death of species.  And to allow, nay, cause the extinction of untold millions of unique and irreplaceable species has got to rank close to the top of all conceivable immoralities.

We humans, as stewards of the earth, have got to get our priorities straight.  We have got to do all that we can to preserve nature by helping to feed humanity; and to do so successfully, we have got to let the air's CO2 content rise.  Any policies that stand in the way of that objective are truly obscene.

Huang, J., Pray, C. and Rozelle, S.  2002.  Enhancing the crops to feed the poor.  Nature 418: 678-684.

Idso, C.D. and Idso, K.E.  2000.  Forecasting world food supplies: The impact of the rising atmospheric CO2 concentration.  Technology 7S: 33-55.

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 years' research.  Agricultural and Forest Meteorology 69: 153-203.

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.

Kimball, B.A.  1983.  Carbon dioxide and agricultural yield: an assemblage and analysis of 430 prior observations.  Agronomy Journal 75: 779-788.

Raven, P.H.  2002.  Science, sustainability, and the human prospect.  Science 297: 954-959.

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

Tilman, D., Cassman, K.G., Matson, P.A., Naylor, R. and Polasky, S.  2002.  Agricultural sustainability and intensive production practices.  Nature 418: 671-677.

Tilman, D., Fargione, J., Wolff, B., D'Antonio, C., Dobson, A., Howarth, R., Schindler, D., Schlesinger, W.H., Simberloff, D. and Swackhamer, D.  2001.  Forecasting agriculturally driven global environmental change.  Science 292: 281-284.

Waggoner, P.E.  1995.  How much land can ten billion people spare for nature?  Does technology make a difference?  Technol. Soc. 17: 17-34.