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| Agriculture and Food Supply |
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 Climate
Impacts on Agriculture and Food Supply
Overview
Agriculture is an important sector of the U.S. economy. The
crops, livestock, and seafood produced in the United States
contribute more than $300 billion to the economy each year.
When food-service and other agriculture-related industries
are included, the agricultural and food sectors contribute
more than $750 billion to the gross domestic product.
Agriculture and fisheries are highly dependent on the
climate. Increases in temperature and carbon dioxide (CO2)
can increase some crop yields in some places. But to realize
these benefits, nutrient levels, soil moisture, water
availability, and other conditions must also be met. Changes
in the frequency and severity of droughts and floods could
pose challenges for farmers and ranchers and threaten food
safety. Meanwhile, warmer water temperatures are likely to
cause the habitat ranges of many fish and shellfish species
to shift, which could disrupt ecosystems. Overall, climate
change could make it more difficult to grow crops, raise
animals, and catch fish in the same ways and same places as
we have done in the past. The effects of climate change also
need to be considered along with other evolving factors that
affect agricultural production, such as changes in farming
practices and technology. |
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 Impacts
on Crops
Crops grown in the United States are critical for the food
supply here and around the world. U.S. farms supply nearly
25% of all grains (such as wheat, corn, and rice) on the
global market. Changes in temperature, atmospheric carbon
dioxide (CO2), and the frequency and intensity of extreme
weather could have significant impacts on crop yields.
Picture - Despite
technological improvements that increase corn yields,
extreme weather events have caused significant yield
reductions in some years. Source: USGCRP (2009)
For any particular crop, the effect of increased temperature
will depend on the crop's optimal temperature for growth and
reproduction. In some areas, warming may benefit the types
of crops that are typically planted there, or allow farmers
to shift to crops that are currently grown in warmer areas.
Conversely, if the higher temperature exceeds a crop's
optimum temperature, yields will decline.
Higher CO2 levels can affect crop yields. Some laboratory
experiments suggest that elevated CO2 levels can increase
plant growth. However, other factors, such as changing
temperatures, ozone, and water and nutrient constraints, may
counteract these potential increases in yield. For example,
if temperature exceeds a crop's optimal level, if sufficient
water and nutrients are not available, yield increases may
be reduced or reversed. Elevated CO2 has been associated
with reduced protein and nitrogen content in alfalfa and
soybean plants, resulting in a loss of quality. Reduced
grain and forage quality can reduce the ability of pasture
and rangeland to support grazing livestock.
More extreme temperature and precipitation can prevent crops
from growing. Extreme events, especially floods and
droughts, can harm crops and reduce yields. For example, in
2010 and 2012, high nighttime temperatures affected corn
yields across the U.S. Corn Belt, and premature budding due
to a warm winter caused $220 million in losses of Michigan
cherries in 2012.
Dealing with drought could become a challenge in areas where
rising summer temperatures cause soils to become drier.
Although increased irrigation might be possible in some
places, in other places water supplies may also be reduced,
leaving less water available for irrigation when more is
needed.
Many weeds, pests, and fungi thrive under warmer
temperatures, wetter climates, and increased CO2 levels.
Currently, U.S. farmers spend more than $11 billion per year
to fight weeds, which compete with crops for light, water,
and nutrients. The ranges and distribution of weeds and
pests are likely to increase with climate change. This could
cause new problems for farmers' crops previously unexposed
to these species.
Though rising CO2 can stimulate plant growth, it also
reduces the nutritional value of most food crops. Rising
levels of atmospheric carbon dioxide reduce the
concentrations of protein and essential minerals in most
plant species, including wheat, soybeans, and rice. This
direct effect of rising CO2 on the nutritional value of
crops represents a potential threat to human health. Human
health is also threatened by increased pesticide use due to
increased pest pressures and reductions in the efficacy of
pesticides. |
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 Impacts
on Livestock
Americans consume more than 36 million metric tons of meat
and poultry annually. Livestock and poultry account for over
half of U.S. agricultural cash receipts, often over $100
billion per year. Changes in climate could affect animals
both directly and indirectly.
Picture - Livestock
locations in the continental United States. Source: USGCRP
(2016)
Heat waves, which are projected to increase under climate
change, could directly threaten livestock. In 2011, exposure
to high temperature events caused over $1 billion in
heat-related losses to agricultural producers. Heat stress
affects animals both directly and indirectly. Over time,
heat stress can increase vulnerability to disease, reduce
fertility, and reduce milk production.
Drought may threaten pasture and feed supplies. Drought
reduces the amount of quality forage available to grazing
livestock. Some areas could experience longer, more intense
droughts, resulting from higher summer temperatures and
reduced precipitation. For animals that rely on grain,
changes in crop production due to drought could also become
a problem.
Climate change may increase the prevalence of parasites and
diseases that affect livestock. The earlier onset of spring
and warmer winters could allow some parasites and pathogens
to survive more easily. In areas with increased rainfall,
moisture-reliant pathogens could thrive.
Potential changes in veterinary practices, including an
increase in the use of parasiticides and other animal health
treatments, are likely to be adopted to maintain livestock
health in response to climate-induced changes in pests,
parasites, and microbes. This could increase the risk of
pesticides entering the food chain or lead to evolution of
pesticide resistance, with subsequent implications for the
safety, distribution, and consumption of livestock and
aquaculture products.
Increases in carbon dioxide (CO2) may increase the
productivity of pastures, but may also decrease their
quality. Increases in atmospheric CO2 can increase the
productivity of plants on which livestock feed. However, the
quality of some of the forage found in pasturelands
decreases with higher CO2. As a result, cattle would need to
eat more to get the same nutritional benefits. |
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 Impacts
on Fisheries
American fishermen catch or harvest five million metric tons
of fish and shellfish each year. U.S. fisheries contribute
more than $1.55 billion to the economy annually (as of
2012). Many fisheries already face multiple stresses,
including overfishing and water pollution. Climate change
may worsen these stresses. In particular, temperature
changes could lead to significant impacts.
Picture - This map
shows the annual centers of biomass for three species in the
northeastern United States from 1968 to 2015. Dots are
shaded from light to dark to show change over time. Source:
US EPA (2016). Climate Change Indicators in the United
States: Marine Species Distribution. Data Source: NOAA
(2016).
The ranges of many fish and shellfish species may change. In
waters off the northeastern United States, several
economically important species have shifted northward since
the late 1960s. The three species shown in [the figure to
the left] (American lobster, red hake, and black sea bass)
have moved northward by an average of 119 miles.
Many aquatic species can find colder areas of streams and
lakes or move north along the coast or in the ocean.
Nevertheless, moving into new areas may put these species
into competition with other species over food and other
resources, as explained on the Ecosystems Impacts page.
Some marine disease outbreaks have been linked with changing
climate. Higher water temperatures and higher estuarine
salinities have enabled an oyster parasite to spread farther
north along the Atlantic coast. Winter warming in the Arctic
is contributing to salmon diseases in the Bering Sea and a
resulting reduction in the Yukon Chinook Salmon, Finally,
warmer temperatures have caused disease outbreaks in coral,
eelgrass, and abalone.
Changes in temperature and seasons can affect the timing of
reproduction and migration. Many steps within an aquatic
animal's lifecycle are controlled by temperature and the
changing of the seasons. For example, in the Northwest
warmer water temperatures may affect the lifecycle of salmon
and increase the likelihood of disease. Combined with other
climate impacts, these effects are projected to lead to
large declines in salmon populations.
In addition to warming, the world's oceans are gradually
becoming more acidic due to increases in atmospheric carbon
dioxide (CO2). Increasing acidity could harm shellfish by
weakening their shells, which are created by removing
calcium from seawater. Acidification also threatens the
structures of sensitive ecosystems upon which some fish and
shellfish rely. |
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 International
Impacts
Climate change is very likely to affect food security at the
global, regional, and local level. Climate change can
disrupt food availability, reduce access to food, and affect
food quality. For example, projected increases in
temperatures, changes in precipitation patterns, changes in
extreme weather events, and reductions in water availability
may all result in reduced agricultural productivity.
Increases in the frequency and severity extreme weather
events can also interrupt food delivery, and resulting
spikes in food prices after extreme events are expected to
be more frequent in the future. Increasing temperatures can
contribute to spoilage and contamination.
Picture - This diagram
shows the impact pathway of carbon dioxide emissions on the
shellfish market. Carbon dioxide is absorbed by oceans,
resulting in ocean acidification. Acidification reduces the
size and abundance of shellfish, which in turn leads to
decreased harvest and eventually to changes in prices for
consumers. Source: US EPA (2015). Climate Change in the
United States: Benefits of Global Action
Internationally, these effects of climate change on
agriculture and food supply are likely to be similar to
those seen in the United States. However, other stressors
such as population growth may magnify the effects of climate
change on food security. In developing countries, adaptation
options like changes in crop-management or ranching
practices, or improvements to irrigation are more limited
than in the United States and other industrialized nations.
Any climate-related disturbance to food distribution and
transport, internationally or domestically, may have
significant impacts not only on safety and quality but also
on food access. For example, the food transportation system
in the United States frequently moves large volumes of grain
by water. In the case of an extreme weather event affecting
a waterway, there are few, if any, alternate pathways for
transport. High temperatures and a shortage of rain in the
summer of 2012 led to one of the most severe summer droughts
the nation has seen and posed serious impacts to the
Mississippi River watershed, a major transcontinental
shipping route for Midwestern agriculture. This drought
resulted in significant food and economic losses due to
reductions in barge traffic, the volume of goods carried,
and the number of Americans employed by the tugboat
industry. The 2012 drought was immediately followed by
flooding throughout the Mississippi in the spring of 2013,
which also resulted in disruptions of barge traffic and food
transport. Transportation changes such as these reduce the
ability of farmers to export their grains to international
markets, and can affect global food prices.
Impacts to the global food supply concern the United States
because food shortages can cause humanitarian crises and
national security concerns. They also can increase domestic
food prices. |
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EPA Page |
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Key Points
Moderate warming and more carbon dioxide in the atmosphere
may help some plants to grow faster. However, more severe
warming, floods, and drought may reduce yields.
Livestock may be at risk, both directly from heat stress and
indirectly from reduced quality of their food supply.
Fisheries will be affected by changes in water temperature
that make waters more hospitable to invasive species and
shift the ranges or lifecycle timing of certain fish
species. |
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Additional Climate Change Information |
Climate Change and Carbon Dioxide
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change
and carbon dioxide.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Carbon Dioxide and Climate Change
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of carbon dioxide
and climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice. |
Environmental Group Warns Earth's Health at Risk
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A report by the World Wildlife Fund looked at thousands of animal populations
and found they have dropped significantly in 40 years. |
Sea Levels Rising at Fastest Rate in 3,000 years
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
A group of scientists say sea levels are rising at record rates. Another group
found that January temperatures in the Arctic reached a record high. |
Capturing CO2 Gas Is Not Easy
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Most scientists agree that carbon-dioxide gas is partly to blame for climate
change: rising global temperatures. But capturing the CO2 gas released by power
stations is costly and difficult. |
Growth, Climate Change Threaten African Plants and
Animals
(Beginner - Listening,
reading)
A video lesson to
help with your understanding of climate change.
The English is
spoken at 75% of normal speed.
Great English listening and reading practice.
Researchers believe Africa may lose as much as 30 percent of its animal and
plant species by the end of this century. |
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