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ICPEP-3 (2005) Souvenir

Global Climate Change and Food Security in a Growing World

Sagar Krupa

Professor Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108, USA


Global climate change is one of utmost international concerns. There is a perception among many that global climate change is simply global warming. In fact, global climate change is an integrated system of several atmospheric phenomena and their products. At the surface, concentrations of greenhouse or radiative gases such as carbon dioxide, chlorofluorocarbons, methane and nitrous oxide have clearly increased since the onset of the industrial revolution. These trace gases, in addition to warming the surface air temperature by trapping some of the energy from the outgoing radiation, when transported into the stratosphere (10-15 km above the surface), destroy the beneficial ozone layer naturally present at that height. Such a loss in the thickness or thinning of the ozone layer will permit the increased penetration to the surface of deleterious wavelengths of solar radiation (Ultraviolet or UV [B- band], 280-315 nanometers, 1 nanometer = one billionth of meter), with much concern for consequent increases in the incidence of melanoma or skin cancer.

Average global air temperature has increased by about 0.8o C above pre-industrial levels and a 2001 report by the Intergovernmental Panel on Climate Change projected a rise from 1.4o C to 5.8o C by the year 2100. While this prediction is extremely important, there is a significant amount of spatial variability in the air temperature. Local climate in different geographic areas may very well become warmer and drier, cooler and wetter or remain unchanged. Any change in the climate is expected to manifest itself as increases in the frequency of extreme events such as hurricanes, blizzards, heat waves and the number of days without precipitation during the plant-growing season (drought).

Increases in air temperature can accelerate crop growth and consequently shorten the growth period. In cereal crops for example, such changes can lead to poor vernalization (e.g., hastened flowering) and reduced yield. There is also evidence that since the 1950s, in North America, in China and in the former Soviet Union, nighttime temperatures have increased much more than the daytime values (because of increased cloud cover due to air pollution and formation of hygroscopic, cloud-forming aerosols in the atmosphere), with the potential to reduce reproductive development in many crop species and consequently, their seed yield.

In developed countries, agriculture is supported by a complex system of research; education, finance and farm supply overlying the agricultural potentials of the arable soils. Public policy and agricultural management will attempt to develop strategies for maintaining crop production in areas with best soils, in spite of shifts in climate. Of equal or greater importance than the direct effects of rising air temperatures is the indirect effect on the hydrologic cycle, leading to shifts in the dependence on irrigation, where water is available. For example, projected drier summers in parts of the USA corn-belt will probably result in a shift from the production of corn to grain sorghum. This has serious economic consequences. Currently USA ranks #1 in the world in corn production (41% of the global production) and the area of its cultivation is on the rise, particularly since it is the largest source for ethanol (through fermentation) used as fuel in automobiles.

In as much as changes in air temperatures will have an impact on crop production, so will increases in the surface concentrations of carbon dioxide and ozone and elevated levels of ultraviolet-B radiation. Most unfortunately, much of our knowledge on these effects is based on experimental studies directed to changes in one variable at a time. Increases in the carbon dioxide concentrations are expected to increase the biomass in many crop species (particularly C3 plants such as soybean and rice, in comparison to C4 plants such as corn and sorghum). However, as seen in the greenhouse production of horticultural crops such as lettuce, increases in biomass may not always translate to acceptable nutritional quality of the consumed product, due to the increases in the accumulation of starch in the foliage at the expense of soluble carbohydrates and decreases in the protein content, unless nitrogen fertilization is practiced. In as much as the beneficial effects of increasing carbon dioxide concentrations on crop production are frequently cited, increasing levels of surface ozone (generated from precursor pollutant emissions, primarily from fossil fuel combustion) and ultraviolet-B radiation produce deleterious effects. Rapidly growing number of studies show that the adverse effects of ozone and ultraviolet-B radiation offset the beneficial effects of carbon dioxide. Since all three variables are on the rise (accounting, however, for their spatial variability), questions remain as to the outcome of their joint effects, superimposed on other climate variables such as shifts in air temperature and soil moisture availability and biotic factors (incidence of pathogens and pests).

While plant canopies serve as a sink for carbon dioxide during photosynthesis (daytime), they are a source during the night due to respiration. Furthermore, soils are a larger source for carbon dioxide due to increased microbial respiration and litter or biomass decomposition under increasing temperatures. Equally importantly agricultural emissions of greenhouse gases are governed by the use of nitrogen fertilizers (increased nitrous oxide emissions from the soil as a greenhouse gas) and animal husbandry (increased ammonia emissions from manure leading to atmospheric nitrogen fertilization by deposition, for example, in precipitation). Those are major concerns in the context of the contribution of agriculture to the climate change issue (warming air temperatures due to the former or shifts in biodiversity due to the latter). In addition, rice paddies are a major source of methane (a greenhouse gas). As populations grow in Asia (by some 29% in 2030), so will the area under rice production, to sustain the food supply.

Clearly the issues associated with deteriorating air quality are a global concern. Satellite data document the spread of aerosols all the way from West Africa to northeastern India to China. India and China rank among the top countries in net human consumption of primary food production. India also ranks at the top in the withdrawal of more than 40% of its total available fresh water supply, in comparison to China (20-40%) and the USA (10­20%). By the year 2050, a majority of the global population is projected to be at a high risk of suffering from water stress. Currently Asia supports more than one half of the global population, with a projected increase of 29% by the year 2030. In comparison, population is expected to increase in Africa by 65%, North America by 26%, and South America by 31% and in contrast, a decrease by 6% is predicted for Europe. The increases in the populations of Asia, Africa and South America are projected to be largely due the birth rates while increases in the US population would be mainly due to immigration.

It is very educative to examine the status of the present and projected global agricultural production within these overall scenarios. Currently the ratio of rural to total populations is for: the world - 52%, China - 65%, India - 71% and the USA - 20%. Similarly the ratio of agricultural to rural populations is for: the world - 80%, China - 94%, India - 73% and the USA - 10%. These are telling statistics of the major dependence of the two most populous countries in the world (China and India) and in addition, some others, on intense human labor for food production and sustainability, compared to the US.

China, India and the US account equally for some 40% of the total area in the world under crop production. Yet the agricultural production in metric tons per capita of the total population is for: the world - 0.26, China - 0.29, India - 0.20 and the USA - 1.4. The large difference between the statistic for the US and the others is due mainly to the use of complex and highly mechanized and managed crop production systems in the US, compared to the emphasis on manual labor elsewhere. In the US these types of statistics have led to some adverse, shortsighted consequences. There has been a progressive decline in the number of individual farmers and a converse increase in corporate mega farming. In addition fluctuations in the commodity prices, the so-called surplus food supply and imports of foreign plant products have worked negatively against the profitability of individual US farmers and thus, the decline in their numbers.

The genetic base of domesticated or cultivated plants is very narrow compared to their wild relatives. Thus, many currently grown crops are considered to be genetically depauperate. Elite lines and hybrids derived from such germplasms are designed to yield well under relatively narrow and well-defined growing conditions. However, superior genotypes are used heavily in various crop-breeding programs, often resulting in considerable relatedness among cultivars grown across large geographic areas, although some cultivars may have more narrow distribution than others.

In general, the narrow genetic base and specific goals used in the breeding of virtually all modern crops make it unlikely that crop breeders will be able to accommodate large and rapid changes in the climate. On the other hand if climate change occurs gradually, production agriculture will be able to adapt to such changes as long as farm resources are not limiting. Nevertheless, if indirect selection of crops to climate change is practiced, it will prove to be an inefficient process. Thus, there will be an increasing need for regions able to sustain high crop production in the future to distribute their surplus food supply to others subjected to adverse impacts, particularly to populations in dire need. That might prove to be a critical determinant of future world populations.

The US agriculture is influenced by: (a) increased urbanization, (b) increasing population migration from rural to urban communities, (c) farming by increased mechanization and consequently decreased dependence on labor, (d) increased area under cultivation of crops developed through the application of biotechnology and consequently better disease, pest and weed control, (e) gain of higher yields and (f) farm consolidation through mergers (mega- corporate farms). In contrast, factors influencing food security in the developing countries include: (a) increasing population, (b) rapidly growing urbanization, (c) decreasing crop land, (d) decreasing farm resources, (e) continuing crop loss, (e) declining crop production and (f) declining biodiversity.

The number of mega cities (greater than 10 million population per city) has increased from 2 in 1950 to 28 in 2004. In 2001, the numbers of poor people (living on $1 or less per day) were concentrated primarily in East Asia, Sub-Saharan Africa and South Asia. During 1998, as equivalents of 1990 $, significant long-term growth in GDP (Gross Domestic Product) per capita was predominantly in Western Europe, Japan, US, Canada and the Oceania. Based on 2003 statistics, according to the Organization of Economic Cooperation and Development (OECD), additional foreign support needed for developing countries to reach 0.5 level of GDP in billions of $, among all developed countries, the US and Japan were the worst in giving aid. In contrast, Sweden and the Netherlands were the most generous with no additional aid required to reach the 0.5 GDP level. Thus, there is a major gap among the main nations of wealth and those that need support for sustainability of their society and their agriculture.

In the final analysis, scientists will continue to study the critical and important issues of the effects of adverse air quality and climate change on crop production. Unfortunately, some scientists have and will use socio-political reasons to further their own cause. Fortunately, in general, those types of activities are transient by nature (e.g., the rise and fall of the acidic precipitation research program in the US during the 1980s and 90s). At the end, sustaining the future global populations through food production and food security would require scientific integrity and a much broader and holistic understanding of the many coupled, but complex facets of our society and their feedbacks to the continuing process of environmental change and its impacts.

As the famous British born American writer, W. H. Auden once noted*:

“Little upon his little earth, man contemplates the universe of which he is both judge and victim”

(W.H. Auden, Commentary)

*According to the author of this article (SK), in a broader sense, the quotation from Auden should not be interpreted as being gender specific.

This article has been reproduced from the Souvenir released during the Third International Conference

on Plants & Environmental Pollution (ICPEP-3) held at Lucknow from  28 November to 2 December 2005.

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