Atmosphere And Weather

Global Warming and the Potential Effects on Crop Growth



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At first glance, global warming seems as though it should benefit crop growth. Where all other factors remain the same, both increased heat and increased carbon dioxide are linked to increased plant growth. However, the full picture is much more complex.

Positive factors

Within normal plant tolerances, warmer temperatures encourage plant growth and speed up development and crop maturation. If other climactic and soil factors remain stable, yields may be higher. Warmer temperatures could potentially allow cultivation of crops with low cold weather tolerance in regions where they could never survive before.

Increased amounts of carbon dioxide and water vapor, both considered common greenhouse gases, also increase plant growth. In fact, greenhouse gases are essential for keeping the earth at a viable temperature by keeping heat from radiating into space. Without greenhouse gases, the average global temperature would be close to 0 degrees Fahrenheit. No plant could survive, and outdoor agriculture would be impossible.

Direct negative factors

The average temperature of the Earth has increased by just over 1 degree over the last century. Most scientists now agree that by the end of this century, the average temperature of the Earth will increase by another 3 degrees. This is a very short period of time for plants to adapt to new conditions.

Current monoculture cultivars are highly specific to the exact climate and growing conditions of a region. These cultivars are the end products of crops which have been bred over thousands of years, to the point where they are no longer capable of propagating themselves without human intervention. Global warming will alter those climates, which will affect global crop yields.

Maximum crop yields can occur only in stable conditions, but stable conditions is exactly what will be lost during climate change. Uneven rises in temperature across the Earth will affect some regions much more strongly and other regions much less. Changes in climate related to the increased heat will also make temperatures more erratic. A late frost is far more devastating after an early, prolonged spring.

Even a slight rise in temperature will also make the weather more erratic. Flood and drought cycles will become more extreme. Areas already prone to droughts or flood will be even more affected. Unless new cultivars and agricultural techiques are developed, marginal areas may become unviable for agriculture.

As the optimal agriculturally productive zones move north, they will move into regions where the topsoil is poorer, thinner, and less suited to large-scale cultivation of staple crops. The axial angle and intensity of the sunlight will also change the intensity and duration of daylight. This combination of factors will shorten or completely eliminate growing seasons in many regions.

Indirect negative factors

Land which can no longer reliably produce the required yield in staple crops is often reallocated to pastureland. However, conversion of cropland to pastureland also magnifies the release of greenhouse gases, especially methane. Methane is up to 72 times as effective in trapping heat as carbon dioxide.

Overuse of vulnerable land as pasture reduces plant cover and damages roots. This leaves the remaining topsoil exposed to the wind. The end result is dust storms, which lead to desertification. Desertification can also be caused by irrigation of arid regions in 3 ways: aquafer depletion, non-local watershed overuse, and increased land salinity.

Shallow aquafers are replenished through rainwater and ground seepage. In an arid region, the amount of water drawn from a shallow aquafer often outstrips its ability to replenish itself. If too much water is drawn from a shallow aquafer where the confining layers are silt or clay, the rock layers around it will push in on the aquafer, making it permanently smaller. Even if the amount of rainfall increases, the aquafer will never again be able to hold as much water as it did before it was depleted. Depletion of an aquafer also causes the land above it to sink, which can lead to structural issues.

Many of the largest aquafers in the world contain paleowater, which was deposited in that aquafer during the end of the last ice age or earlier. When paleowater is tapped, replenishment of the aquafer can only happen on a geological scale. On a human timescale, the water will run out.

Irrigation which taps water from a non-local watershed permanently diverts the water away from that watershed. If the diversion is greater than the ability of the watershed to replenish itself through rain and glacial melt, even a very large lake or sea can dry up. The Aral Sea was once larger than most of the Great Lakes. Now it is less than a tenth of its former size. If too much of their water is diverted for irrigation into the Mississippi River watershed, the Great Lakes are at similar risk.

The loss of the watershed will permanently alter the climate of the region. As a result, both the area under irrigation and the former watershed will become more arid.

All water has some dissolved minerals. As the water is absorbed by plants and then evaporates, the dissolved mineral salts remain behind. This increases the salinity of irrigated soil. Eventually the salinity of the soil will be greater than the crops can tolerate.

Final assessment

If new cultivars cannot be developed in time and agricultural practices do not change to follow suit, the effect on crops is likely to be severe. Many regions of the world will lose between 10% and 30% of their staple crops due to the changes in rainfall alone. Africa, Asia, and Australia will feel the severest effects of loss of rainfall.

Most of North America and Europe will less affected on average, at least at first. However, extremes of weather will become more common, which will result in larger crop losses due to heat, drought, flood, and frost.

Many climatologists believe that a global rise in temperature will also increase the number of severe storms, which are driven by heat differentials. Although the effect will be global, the geography of North America, with its north-south mountain ridges, is particularly vulnerable to developing severe storms over land. According to agricultural insurance statistics, each year has been more costly than the last, above and beyond the cost of inflation. This trend can be expected to continue.

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