Agricultural Shifts
Image © 2009 Jupiterimages
Corporation.The central part of the United States is one of the world's great agricultural regions. Its rich soils
and favorable climate produce high yields of corn, soybeans, and wheat. As farming techniques
have advanced, farmers have steadily increased yields for these crops over the last century.
These continuing efforts to increase yields make it difficult to determine whether or how climate
change has affected agriculture thus far, but studies on plant characteristics
offer insights as to what farmers might expect from future climate
change.
In general, plants grow faster in warmer climates, which
could be good news for some farmers, especially in
temperate and cold areas. But this applies only up
to a point. When it gets too warm, crops tend to
mature too early, and under extreme conditions,
high temperatures can kill crops. Although different
varieties are bred to withstand certain conditions,
each crop ultimately has a limited temperature
range.
Plants are also affected by the amount of carbon
dioxide in the atmosphere. Yields of some
crops, such as soybeans and wheat, increase with
higher levels of carbon dioxide in the atmosphere,
while yields of others, such as sugarcane and corn,
do not. Unfortunately for nature lovers who enjoy hiking
and exploring, some pest plants—for example, poison
ivy—grow faster and produce more irritant when atmospheric
carbon dioxide is higher.
Most models conclude that if warming stays within the low-to-mid temperature
range of climate change predictions, crop yields will probably increase in the central United
States by 5 to 20 percent. But the balance between the effects of warming and the effects of
increased carbon dioxide will likely mean increased yields for some crops and decreases for
others. Climate change may also alter the dynamics of weeds and other pests and affect the frequency
of severe weather events.
How farmers adapt to a changing climate will be a critical factor in future yields. Aggressive
action to adjust farming methods, planting dates, and selection of which crops or varieties to
grow in response to changing climate conditions can play a large role in future crop yields.
Good information about future changes and adaptive measures will be crucial for helping farmers
cope effectively with climate change.
Migratory Waterways
These shallow, temporary lakes scattered throughout
the Midwest provide critical places for migrating
birds
to rest, feed, and mate.
Image courtesy of the U.S.
Fish and Wildlife Service.Did you know that the central United States is a critical corridor for millions of migratory birds?
During long and exhausting migrations, these birds rest, feed, and mate in a string of small,
shallow lakes called "playa lakes" or "prairie potholes." This migration route is especially critical
for mallard ducks and other waterfowl, whose yearly populations closely correspond to the
number of playa lakes that are available at the beginning of the breeding season.
These crucial watering holes naturally come and go with changing seasons and precipitation
patterns. Already under pressure from farmers who use them for irrigation water, from people
who fill them in to create more land for crops or houses, and from contaminated runoff of nutrients
and pesticides, these essential but transient habitats are expected to face increased stress
due to climate change. A combination of higher temperatures and lower rainfall could literally
dry up the playa lakes in six states, posing a significant threat to the birds that depend on them.
This web page is based on the National Academies' educational booklet
Ecological Impacts of Climate Change.
