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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. |
