The Response Of Agriculture To Climate Change

According to the Pew Center on Global Climate Change, agricultural production will experience a mixture of positive or negative effects that will depend on the geography and specific conditions of the area. The

Pew Center, established in 1998, is a nonpartisan, independent research organization. The center's mission is to provide credible information, straight answers, and innovative solutions in the effort to address global climate change. Future predictions from global warming models have predicted higher temperatures as well as higher precipitation in certain areas.

The effect of increased temperature can have either a positive or negative effect, based on geography. For instance, for the colder high-latitude locations such as Alaska and Canada, warmer temperatures would enable the existence of longer growing seasons. This could encourage the possibility of extended growing seasons as long as soil conditions are adequate. If soil conditions are not adequate and are not fertile enough (lacking proper nutrients and soil structure) to support the growth of crops, the length of the growing season will not matter because growing crops would not be successful. Adding large doses of fertilizer to increase fertility is also not a good option because they can have negative effects on the environment, such as being washed off into the drainage and entering and polluting the water cycle and biogeo-chemical systems.

In more southern latitude locations, warmer temperatures would be beneficial if they eliminated the killing frosts that can currently destroy crops. This could potentially enable citrus crops to be grown farther north. The U.S. Department of Agriculture warns, however, that high temperatures could shorten the critical growing period interval, limiting the successful growth of large crop yields.

Changes in precipitation may also have positive and negative effects. Increased precipitation in the traditionally arid areas such as the American Southwest would benefit them by enabling growing periods to exist. On the other hand, precipitation increase in areas where it results in flooding would be a disaster, causing erosion and loss of land and resources. In other geographical locations that experience a shortfall of precipitation, drought and water shortage would cause havoc with agricultural production.

Increasing levels of CO2 in the atmosphere usually increases the net photosynthetic rates in plants, as well as reduces transpiration loss. Because the photosynthesis rate is enhanced in plants as atmospheric

CO2 increases, vegetation productivity rises. The specific reaction to increased CO2 to each plant varies by plant species. Based on findings at the Pew Center, the main commercial crops grown in the United States are wheat, rice, potatoes, barley, oats, and a wide variety of vegetables, which typically respond well to an increase in CO2. With a modeled increase of a doubled level of CO2, crops in the United States would be expected to generally increase quantities by 15 to 20 percent. On the other hand, the tropical vegetation species—or warm weather crops—such as sugarcane, sorghum, corn, and tropical grasses are much less responsive and estimates of only 5 percent are expected.

The difficult aspect of this modeling is that some scientists believe crop productivity is also significantly difficult to predict because CO2 is also influenced by other things such as nutrients and water availability, which makes it more difficult to predict the future. In computer modeling done by the Intergovernmental Panel on Climate Change (IPCC), the estimated effects of global warming on agricultural resources will vary from crop to crop and geographic region to geographic region, as shown in the following table.

General predictions have been made that areas that experience large temperature changes will experience more negative effects. Countries in the mid- and high-latitude areas may experience an enhanced CO2 effect accompanied by an increase in agricultural production; but yields in low-latitude countries such as Brazil may actually see a decline in agricultural production, especially with commodities such as corn and wheat, as drought becomes more likely. The commodity that seems to be the most resilient to climate change is rice. According to the IPCC, specific temperature ranges may also play an important role. For instance, areas that increase up to 3.6°F (2°C) are the areas that may experience positive crop yields. Areas that have an increase of 7.2°F (4°C), on the other hand, may actually see less production.

Livestock are also greatly affected by global warming. They can be affected in two major ways: (1) by the quantity of grazable land and whether there is enough to support the number of livestock on it; (2) the quality of grazable land—the types and abundance of forage available for the health of the livestock living on the land. Global warming can seriously affect both of these variables.

Estimated Climate Change Effects on Crop Yields in Latin and North America

LOCATION OF STUDY SITE

IMPACT (CROP: PERCENT CHANGE IN YIELD)

North America:

Canada

Wheat: -40% to +234% (results vary due to geographic location)

United States

Corn: -30% to -15% Wheat: -20% to -2% Soybean: -40% to +15%

Latin America:

Argentina

Corn: -36% to -17% Wheat: +3% to +48% Soybean: -3% to -8%

Brazil

Corn: -25% to -2% Wheat: -50% to -15% Soybean: -61% to -6%

Mexico

Corn: -61% to -6%

Note: Increases are due to cooler areas becoming warmer and more conducive to the growth of crops; decreases are due to areas becoming more arid and less conducive to the growth of crops. Source: IPCC

Another variable that can affect livestock is the encroachment of invasive species and pests. As temperatures warm, invasive plants, grasses, and weeds can overtake rangeland biomes. If these invasive species are not foods that grazing livestock can eat, the food supply is threatened, hence, their survival. Extreme weather can also play a significant role in the health and well-being of livestock. As global warming progresses, it is expected that severe weather episodes will increase, such as blizzards, flooding, heat waves, and drought. Each of these

Cattle grazing on open rangeland in the western United States

(Bureau of Land Management)

Cattle grazing on open rangeland in the western United States

(Bureau of Land Management)

weather events and climate conditions can have a negative impact as well, as evidenced by what occurred during the 1996-97 winter season in the northern plains of the United States. During that winter, severe blizzards and accompanying freezing temperatures took a devastating toll on the livestock. In the American Southwest, several years of drought from 2001 through 2005 drastically lowered the carrying capacity of the land for the grazing of cattle and sheep. Winter snow-packs in the mountains were unseasonably low, resulting in a low, early spring runoff. Drought conditions caused what little vegetation there was to dry up and die quickly, leaving livestock without forage to graze on. What scarce, brittle vegetation was left was then highly susceptible to wildfire caused by both lightning strikes and human carelessness, making summers prone to high incidences of damage by fire. The summer and fall of 2007 was one of the most devastating periods of wildfire due to dried-out, drought-stricken vegetation.

According to the Pew Center, another undesirable effect related to high temperatures is that under these conditions, livestock's appetites are suppressed, causing lower weight gain. Based on studies conducted by R. M. Adams (Department of Agriculture and Resource Economics, Oregon State University), J. D. Glyer (Christensen and Associates, Madison, Wisconsin), and B. A. McCarl (Texas A&M University), with a 9°F (5°C) increase in temperature cow/calf herd population in the United States dropped by 10 percent.

Another team of scientists—J. D. Hanson (USDA), B. B. Baker (USDA), and R. M. Bourdon (Department of Animal Sciences, Colorado State University)—found that a warming of 2.7°F (1.5°C) causes a 1 percent loss of livestock herds. They also found that the herds were less productive and did not produce as much milk. In this study, the scientists concluded that the negative effects were caused by both the increased temperature and lack of forage.

The Pew Center on Global Climate Change has also identified some indirect effects of climate change on agriculture. One of the most significant is soil erosion and degradation. The effects of flooding, drought, and wind erosion can have devastating effects on crop yields.

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