Food vs. nature

From ClimateWiki

From Climate Change Reconsidered, a work of the Nongovernmental International Panel on Climate Change

Norman Borlaug, the father of the Green Revolution, recently expressed in a Science editorial his concern over the challenge of “feeding a hungry world” by noting that “some 800 million people still experience chronic and transitory hunger each year,” and that “over the next 50 years, we face the daunting job of feeding 3.5 billion additional people, most of whom will begin life in poverty” (Borlaug, 2007). He described how the scientific and technological innovations he played a major role in discovering and implementing helped reduce the proportion of hungry people in the world “from about 60% in 1960 to 17% in 2000.” Had that movement failed, he says, environmentally fragile land would have been brought into agricultural production and the resulting “soil erosion, loss of forests and grasslands, reduction in biodiversity, and extinction of wildlife species would have been disastrous.”

Rising CO2 concentrations in the air helped make it possible to feed a growing global population in the past without devasting nature, but what of the future? The world’s poulation in 2008 was estimated to be 6.7 billion and is projected to reach between 9.1 and 9.7 billion by 2050 (United Nations, 2009; U.S. Census Bureau, 2008). There is real concern about our ability to feed the world’s population a mere 50 years hence.

Tilman et al. (2001) analyzed the global environmental impacts likely to occur if agriculture is to keep pace with population growth. They report that “humans currently appropriate more than a third of the production of terrestrial ecosystems and about half of usable freshwaters.” They estimate that the amount of land devoted to agriculture by the year 2050 will have to increase 18 percent to meet the rising demand for food. Because developed countries are expected to withdraw large areas of land from farming over the next 50 years for recreation, open space, and reforestration, the net loss of natural ecosystems to cropland and pasture in developing countries will amount to about half of all potentially suitable remaining land, which would “represent the worldwide loss of natural ecosystems larger than the United States.” Similar warnings of a coming food vs. nature conflict have been expressed by other scientists, for example, Wallace (2000) and Raven (2002).

What, if anything, can be done to address this conflict between the need to produce food and the wish to preserve nature? And what role, if any, will climate change play in averting the crisis or making it even worse?

We begin by observing that the fear that there isn’t enough land to support a growing population’s food needs is a very old one, dating at least to Thomas Malthus (1798) and expressed in our day by popular writers such as Paul Ehrlich (2008) and Al Gore (1992). Predictions of widespread famine have been wrong before, as trends in food production and daily intake of calories per capita, while not linear in the short term, show long-term positive trends that are driven primarily by gains in yields per acre, not expansion of the area under cultivation (Alexandratos, 1995; Goklany, 1999; Waggoner and Ausubel, 2001). Malthusian concerns are misplaced because, as Max Singer once explained, “multiplying food production by five times over the next one hundred or two hundred years will be easier than multiplying it by over seven times as we did in the last two hundred years. No miracles, no scientific breakthroughs, no unknown lands or unexpected new resources, and no reforms of human character or government are required. All that is required is a continuing use of current evolutionary processes in technology and in economic dvelopment, and as much peace as we have had in the last century” (Singer, 1987).

We also agree with the sensible assessment of science writer Gregg Easterbrook that “the whole notion that there is a proper level of population for Homo sapiens, or for any species, would be nonsensical to nature” and “there is no reason in principle that the Earth cannot support vastly more human beings than live upon it today, with other species preserved and wild habitats remaining intact” (Easterbrook, 1995). Similar sentiments have been expressed by Waggoner (1995, 1996), Waggoner et al. (1996), and Meyer and Ausubel (1999).

Regardless of whether the goal of feeding a growing population while protecting nature is attainable, the question remains about global warming’s role in this very real conflict. Tilman and a second set of collaborators, writing a year after their previously cited analysis, said “raising yields on existing farmland is essential for ‘saving land for nature’” (Tilman et al. (2002). They proposed a three-part strategy: (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 efforts— increasing crop yield per unit of land area—the researchers note that in many parts of the world the historical rate-of-increase in crop yield is declining as the genetic ceiling for maximal yield potential is being approached. This “highlights the need for efforts to steadily increase the yield potential ceiling.” With respect to the second effort—increasing crop yield per unit of nutrients applied—they note that “without the use of synthetic fertilizers, world food production could not have increased at the rate [that it did in the past] and more natural ecosystems would have been converted to agriculture.” Hence, they say the solution “will require significant increases in nutrient use efficiency, that is, in cereal production per unit of added nitrogen.” With respect to the third effort—increasing crop yield per unit of water used—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.”

The ongoing rise in the atmosphere’s CO2 concentration will help the world’s farmers achieve all three parts of the Tilman strategy. First, since atmospheric CO2 is the basic “food” of nearly all plants, the more of it there is in the air, the better they function and the more productive they become. As discussed in Section 9.2, a 300 ppm increase in the atmosphere’s CO2 concentration would increase the productivity of earth’s herbaceous plants by 30 to 50 percent (Kimball, 1983; Idso and Idso, 1994) and the productivity of its woody plants by 50 to 80 percent (Saxe et al., 1998; Idso and Kimball, 2001). These increases will be in addition to whatever yield gains are made possible by advances in plant genetics, pest control, and other agricultural practices. Consequently, as the air’s CO2 content continues to rise, so too will the land-use efficiency and productive capacity of the planet improve.

Regarding the second strategy, of increasing crop yield per unit of nutrients applied, many studies have investigated the effects of an increase in the air’s CO2 content on plants growing in soils with different nitrogen concentrations. (See Chapter 7, Section 7.3.7, for a thorough review of these studies.) These studies found that many plants increase their photosynthetic nitrogen-use efficiency when atmospheric CO2 concentration is raised. For example, Smart et al. (1998) found wheat grown in controlled-environment chambers maintained at an atmospheric CO2 concentration of 1,000 ppm increased average plant biomass by approximately 15 percent, irrespective of soil nitrogen content.

Zerihun et al. (2000) studied the effects of CO2 enrichment on sunflowers using three different soil nitrogen concentrations and found whole plant biomass values that were 44, 13 and 115 percent greater than those of the plants growing in ambient air at low, medium and high levels of soil nitrogen, respectively. Deng and Woodward (1998) found that strawberries grown in high CO2 environments produced 17 percent greater fresh fruit weight even when receiving the lowest levels of nitrogen fertilization. Newman et al. (2003) investigated the effects of two levels of nitrogen fertilization and an approximate doubling of the air’s CO2 concentration on the growth of tall fescue, an important forage crop. They found the plants grown in the high-CO2 air and under low N conditions photosynthesized 15 percent more and produced 53 percent more dry matter (DM).

Demmers-Derks et al. (1998) grew sugar beets at atmospheric CO2 concentrations of 360 and 700 ppm and high and low nitrogen treatment levels, and found the extra CO2 enhanced total plant biomass by 13 percent even in plants receiving the low nitrogen treatments. Also working with sugar beets, Romanova et al. (2002) doubled atmospheric CO2 concentrations while fertilizing plants with three different levels of nitrate-nitrogen. The plants exhibited rates of net photosynthesis that were approximately 50 percent greater than those displayed by the plants grown in ambient air, regardless of soil nitrate availability.

Fangmeier et al. (2000) grew barley plants in containers at atmospheric CO2 concentrations of either 360 or 650 ppm and either a high or low nitrogen fertilization regime. The elevated CO2 had the greatest relative impact on yield when the plants were grown under the less-than-optimum low-nitrogen regime, i.e., a 48 percent increase vs. 31 percent under high-nitrogen conditions.

Finally, the review and analysis of Kimball et al. (2002) of most FACE studies conducted on agricultural crops since the introduction of that technology back in the late 1980s found that in response to a 300-ppm increase in the air’s CO2 concentration, rates of net photosynthesis in several C3 grasses were enhanced by an average of 46 percent under conditions of ample soil nitrogen supply and by 44 percent when nitrogen was limiting to growth. Clover experienced a 38 percent increase in belowground biomass production at ample soil nitrogen, and a 32 percent increase at low soil nitrogen. Wheat and ryegrass experienced an average increase of 18 percent at ample nitrogen, while wheat experienced only a 10 percent increase at low nitrogen.

Other studies have found that many species of plants respond to increases in the air’s CO2 content by increasing fine-root numbers and surface area, which tends to increase total nutrient uptake under CO2-enriched conditions (Staddon et al., 1999; Rouhier and Read, 1998; BassiriRad et al., 1998; and Barrett et al., 1998). This once again advances the Tilman strategy of increasing crop yield per unit of available nutrient. (See Chapter 7, Section 7.8.2, for a thorough review of those studies.)

Tilman’s third strategy—increasing crop yield per unit of water used—is also advanced by rising levels of CO2 in the atmosphere. Plants exposed to elevated levels of atmospheric CO2 generally do not open their leaf stomatal pores—through which they take in carbon dioxide and give off water vapor—as wide as they do at lower CO2 concentrations and tend to produce fewer of these pores per unit area of leaf surface. Both changes tend to reduce most plants’ rates of water loss by transpiration. The amount of carbon they gain per unit of water lost—or water-use efficiency—therefore typically rises, increasing their ability to withstand drought.

In the study of Serraj et al. (1999), soybeans grown at 700 ppm CO2 displayed 10 to 25 percent reductions in total water loss while simultaneously exhibiting increases in dry weight of as much as 33 percent. Likewise, Garcia et al. (1998) determined that spring wheat grown at 550 ppm CO2 exhibited a water-use efficiency that was about one-third greater than that exhibited by plants grown at 370 ppm CO2. Hakala et al. (1999) reported that twice-ambient CO2 concentrations increased the water-use efficiency of spring wheat by 70 to 100 percent, depending on experimental air temperature.

Hunsaker et al. (2000) reported CO2-induced increases in water-use efficiency for field-grown wheat that were 20 and 10 percent higher than those displayed by ambiently grown wheat subjected to high and low soil nitrogen regimes, respectively. Also, pea plants grown for two months in growth chambers receiving atmospheric CO2 concentrations of 700 ppm displayed an average water-use efficiency that was 27 percent greater than that exhibited by ambiently grown control plants (Gavito et al., 2000). (See Chapter 7, Section 7.2, for a thorough review of those studies.)

An issue related to water-use efficiency that could become more important in the future is the buildup of soil salinity from repeated irrigations, which can sometimes reduce crop yields. Similarly, in natural ecosystems where exposure to brackish or salty water is commonplace, saline soils can induce growth stress in plants not normally adapted to coping with this problem. The studies reported below show that rising atmospheric CO2 concentrations also can help to alleviate this problem.

Mavrogianopoulos et al. (1999) reported that atmospheric CO2 concentrations of 800 and 1200 ppm stimulated photosynthesis in parnon melons by 75 and 120 percent, respectively, regardless of soil salinity, which ranged from 0 to 50 mM NaCl. Atmospheric CO2 enrichment also partially alleviated the negative effects of salinity on melon yield, which increased with elevated CO2 at all salinity levels.

Maggio et al. (2002) grew tomatoes at 400 and 900 ppm in combination with varying degrees of soil salinity and noted that plants grown in elevated CO2 tolerated an average root-zone salinity threshold value that was about 60 percent greater than that exhibited by plants grown at 400 ppm CO2 (51 vs. 32 mmol dm-3 Cl). The review of Poorter and Perez-Soba (2001) found no changes in the effect of elevated CO2 on the growth responses of most plants over a wide range of soil salinities, in harmony with the earlier findings of Idso and Idso (1994).

These various studies suggest that elevated CO2 concentrations will help farmers achieve all three of the strategies Tilman et al. say are essential to addressing the conflict between feeding a growing human population and preserving space for nature. The actual degree of crop yield enhancement likely to be provided by the increase in atmospheric CO2 concentration expected to occur between 2000 and 2050 has been calculated by Idso and Idso (2000) to be sufficient—but just barely—to close the gap between the supply and demand for food some four decades from now. Consequently, letting the evolution of technology take its course—which includes continued emissions of CO2 into the atmosphere by industry—appears to be the only way we can grow enough food to support ourselves in the year 2050 without taking unconscionable amounts of land and freshwater resources from nature.

In spite of the dilemma described above and the fact that enhanced levels of CO2, in the air are a necessary part of the solution, the IPCC calls for strict measures to reduce anthropogenic CO2 emissions—a strategy that, if it has any effect at all on plant and animal life, would lead to lower land-use efficiency, lower nitrogen-use efficiency, and lower plant water-use efficiency, just the opposite of what Tilman et al. called for.

One might ask whose predictions are more reliable, the IPCC’s computer-model-generated forecasts of catastrophic consequences due to rising temperatures a century or longer from now, or our projections of human population growth and agricultural productivity just four decades into the future? In addition to the obvious time differential between the two sets of predictions, human population growth and agricultural productivity are much better-understood processes than is global climate change, which involves a host of complex phenomena that span a spatial scale of fully 14 orders of magnitude, ranging from the planetary scale of 107 meters to the cloud microphysical scale of 10-6 meter.

Many of the component processes that comprise today’s state-of-the-art climate models are so far from adequately understood (see Chapters 1 and 2) that even the signs of their impacts on global temperature change (whether positive or negative) are not yet known. Consequently, in light of the much greater confidence that can realistically be vested in demographic and agricultural production models, it would seem that much greater credence can be placed in our predictions than in the predictions of climate doom.

In conclusion, the aerial fertilization effect of the increase in the air’s CO2 content that is expected to occur by the year 2050 would boost crop yields by the amounts required to prevent mass starvation in many parts of the globe, without a large-scale encroachment on the natural world. Acting prematurely to reduce human CO2 emissions, as urged by the IPCC, could interrupt this response, resulting in the death by starvation of millions of people, loss of irreplaceable natural ecosystems, or both.

Additional information on this topic, including reviews of newer publications as they become available, can be found at http://www.co2 science.org/subject/f/food.php.

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