Climate Change Impacts for the Agricultural Sector in the United States

Weather and climate factors such as temperature, precipitation, CO2 concentrations, and water availability directly impact the health and well-being of plants, pasture, rangeland, livestock and fisheries. Climate affects variation in yield, insects, disease, and weeds, which in turn affect agricultural production. Farmers in the United States may face increasing uncertainty and risk as they attempt to adapt to the effects of climate change relating to:

1. Warming temperatures and drought

2. Extreme weather events and flooding

3. Sea level rise

4. Increasing Carbon Dioxide (CO2)

In the following the first aspect is described in more detail.

Warming Temperatures and Drought

Warming temperatures will have significant effects on the agriculture sector. Impacts from climate change for crops include decreasing yield, obsolescence of certain varieties, and increased needs for both land conservation and water management strategies. For livestock, decreases in production and yield are also expected. A predicted increase in pests and insects, as well as the migration of invasive plant species, will threaten both crops and livestock.

Temperature increases will cause the optimum latitude for crops to move northward. Where plants can be efficiently grown depends upon climate conditions, of which temperature is one of the major factors. Higher temperatures will mean a longer growing season for crops that do well in the heat, such as melon, okra, and sweet potato, but a shorter growing season for crops more suited to cooler conditions, such as potato, lettuce, broccoli, and spinach. Parts of the Northeast are projected to become unsuitable for growing certain popular varieties of apples, blueberries, and cranberries by late this century, since these plants require long winter-chill periods to produce fruit. Warming temperature may affect the maturity and yield of certain crops. Exposure to high temperatures during the grain, fiber, or fruit production period leads to lower productivity and decreased quality. Shifts in plant productivity and type will likely also have significant impact on livestock operations as a foraging input for feeding livestock. Higher temperatures also cause plants to use more water to keep cool. A longer growing season may allow farmers to experiment with new crops, but many traditional farm operations in the region will become unsustainable without adaptation strategies that could be quite costly.

Temperature extremes will also pose problems. Even crop species that are well-adapted to heat, such as tomatoes, can have reduced yield and/ or quality when daytime maximum temperatures exceed 90°F for even short periods during critical reproductive stages. For many high-value crops, just hours or days of moderate heat stress at critical growth stages can reduce grower profits by negatively affecting visual or flavor quality, even when total yield is not reduced.

Weeds, diseases, and insect pests benefit from warming, and weeds also benefit from a higher carbon dioxide concentration, increasing stress on crop plants and requiring more attention to pest and weed control. One concern with continued warming is the northward expansion of invasive weeds, such as kudzu. Controlling weeds currently costs the United States more than $11 billion a year, with the majority spent on herbicides. As temperatures and carbon dioxide levels rise, higher concentrations and more frequent spraying of herbicides will be needed, increasing economic and environmental costs associated with chemical use. Many insect pests and crop diseases thrive due to warming, increasing losses and necessitating greater pesticide use. Warming aids insects and diseases in several ways. Rising temperatures allow both insects and pathogens to expand their ranges northward. In addition, rapidly rising winter temperatures allow more insects to survive over the winter, whereas cold winters once controlled their populations.

Higher temperatures will very likely reduce livestock production during the summer season, but these losses may be partially offset by warmer temperatures during the winter season. For ruminants, current management systems generally do not provide shelter to buffer the adverse effects of changing climate; such protection is more frequently available for non-ruminants (e.g., swine and poultry). Disease pressure on domestic animals will likely increase with earlier springs and warmer winters, which will allow proliferation and higher survival rates of pathogens and parasites. Regional variation in warming and changes in rainfall will also affect spatial and temporal distribution of disease.

Regarding aquaculture and fisheries, the distribution of marine fish and plankton are predominantly determined by climate, so marine species in U.S. waters are moving northward and the timing of plankton blooms is shifting. Commercial fishermen and researchers have already observed shifting distributions of fish and invertebrates as ocean temperatures change. Warm surface waters are also pushing some fish towards deeper waters. Species that were previously unable to establish populations because of cold winters are likely to find the warmer conditions more welcoming and gain a foothold, particularly as native species are under stress from climate change and other human activities. Intense human uses have taken a toll on coastal environments and their resources. Many fish stocks have been severely diminished by over-fishing and large “dead zones” depleted of oxygen have developed as a result of pollution by excess nitrogen runoff. Coastal dead zones in places such as the northern Gulf of Mexico and the Chesapeake Bay are likely to increase in size and intensity as warming increases, unless efforts to control runoff of agricultural fertilizers are redoubled.

Drought frequency and severity are projected to increase in the future over much of the United States, making irrigation essential for most high-value crops. Increased drought will be occurring at a time when crop water requirements also are increasing due to rising temperatures. Water deficits are detrimental for all crops. An increase in dry spells, heat waves, and sustained droughts could result in major impacts on crop and livestock growth as well as productivity.


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