How does rising atmospheric CO2 affect marine organisms?

Learn how plants respond to higher atmospheric CO2 concentrations

Click to locate material archived on our website by topic


Expanding the Biosphere's Limits to Growth
Volume 16, Number 1: 2 January 2013

In a brief "Perspective" recently published in Science, Running (2012) resurrects shades of Meadows et al.'s 1972 treatise on The Limits to Growth. Noting that "terrestrial plant production is the foundation of the biospheric carbon cycle" and that "water and atmospheric CO2 are transformed into plant carbohydrate matter with the help of solar energy," he states that this plant matter "sustains the global food web and becomes the source of food, fiber and fuel for humanity."

A problem that Running sees in these facts, however, is that for more than 30 years, global net primary production (NPP) "has stayed near 53.6 Pg per year, with only ~1 Pg of inter-annual variability," citing two studies of which he was a co-author (Nemani et al., 2003; Zhao and Running, 2010). And he thus goes on to speculate that "if global NPP is fixed by planetary constraints, then no substantial increase in plant growth may be possible."

If true, this result would have catastrophic consequences, for it is almost universally agreed, as Running writes, that "the projected 40% increase in human population by 2050 CE, combined with goals to substantially improve standards of living for the poorest 5 billion people on Earth, implies at least a doubling of future resource demand by 2050," the most important of which resources is food.

But is a doubling of food production a mere 38 years from now realistic? Agriculture already consumes 38% of the world's land surface; and Running says that "many analyses now conclude that freshwater use for irrigation has already reached a planetary boundary." Furthermore, with "massive river pollution and ocean anaerobic dead zones," he states that "if anything, future increases in NPP must be achieved with less, not more, irrigation and fertilizer use." And God help us if, as he also notes, "land previously allocated to food production is transformed to bioenergy production, raising food prices for the people who can least afford it," as discussed by Tilman et al. (2010).

So, have we really reached the planet's limits to growth? In a paper recently published in Nature entitled "Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years," Ballantyne et al. (2012) suggest not. The five U.S. scientists say their mass balance analysis shows that "net global carbon uptake has increased significantly by about 0.05 billion tonnes of carbon per year and that global carbon uptake doubled, from 2.4 0.8 to 5.0 0.9 billion tonnes per year, between 1960 and 2010." And they thus conclude that "there is no empirical evidence that carbon uptake has started to diminish on the global scale." In fact, as their results clearly indicate, just the opposite appears to be the case, with global carbon uptake actually doubling over the past half-century.

But how can that be? There are many answers: breeding of better crop varieties that are higher-yielding, more competitive with weeds, less tasty to insect pests, more nutritious, more drought resistant, as well as smarter ways of farming, improved technologies, and the worldwide aerial fertilization and transpiration-reducing effects of the historical and still-ongoing rise in the air's CO2 content, which latter phenomena benefit both agriculture and the world of nature at one and the same time.

So rather than allocate precious land and water resources to the production of biofuels, which diminishes our ability to produce the enormous amounts of extra food we will need to feed ourselves every year for the next four decades and beyond, and which drives up the cost of the foods that we are able to produce, we suggest that we concentrate on using our great stores of coal, gas and oil to meet our future fuel needs, as these substances are clearly the least expensive energy sources we currently possess, and the utilization of all of them will result in lower costs of most all of the products and services that small and large businesses alike provide. And perhaps most important of all, more carbon dioxide in the atmosphere will boost the water use efficiencies and yields of essentially all agricultural crops everywhere, as well as the robustness of the entire world of nature.

Sherwood, Keith and Craig Idso

References
Ballantyne, A.P., Alden, C.B., Miller, J.B., Tans, P.P. and White, J.W. 2012. Increase in observed net carbon dioxide uptake by land and oceans during the past 50 years. Nature 488: 70-72.

Meadows, D.H., Meadows, D.L., Randers, J. and Behrens III, W.W. 1972. The Limits to Growth. Universe Books, New York, New York, USA.

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.

Running, S.W. 2012. A measurable planetary boundary for the biosphere. Science 337: 1458-1459.

Tilman, D., Socolow, R., Foley, J.A., Hill, J., Larson, E., Lynd, L., Pacala, S., Reilly, J., Searchinger, T., Somerville, C. and Williams, R. 2009. Beneficial biofuels: The food, energy, and environment trilemma. Science 325: 270-271.

Zhao, M. and Running, S.W. 2010. Drought-induced reduction in global terrestrial net primary production from 2000 through 2009. Science 329: 940-943.