• by Perry Beeman* - IPS/IFEJ (des moines, iowa)
• Tuesday, July 13, 2010
• Inter Press Service

Climate change is expected to disrupt agriculture in the U.S. Midwest, with high carbon dioxide promoting crop growth but stronger storms, drought, floods and migrating yields dampening yields.

Overall, there are signs that crops will be stressed, and that weeds and insects will change their range. The Midwest climate has already become wetter and warmer, said Gene Takle, an atmospheric scientist at Iowa State University. That could mean a longer crop-growing season and savings on air conditioning, but it doesn't necessarily guarantee higher crop yields.

Takle's model predicts that precipitation in the Midwest will increase by 21 percent by the 2040s, with stream flows climbing by 50 percent in the same period.

His findings are similar to those of the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Global Change Research Programme. Leaders in the breadbasket states have debated how best to respond, from cutting back on coal power to boosting wind energy, which has grown sharply in places like Iowa.

'Climate change is happening at a much greater and accelerated pace than we ever expected 30 years ago,' said Richard Leopold, director of the Iowa Department of Natural Resources.

Huge floods in 2008, which left the state's second-biggest city, Cedar Rapids, with massive downtown destruction, intensified the debate, with a new set of recommendations coming from a state panel by the end of the year.

'If we decide as a state to significantly reduce greenhouse gas emissions in a hurry, we can actually do it,' said Sen. Rob Hogg, a Democrat from Cedar Rapids. 'There are a lot of things we can do for no cost, and others we can do for very little cost.'

One of Takle's studies used Iowa's experience to show the stress already showing up in the Midwest states, which are major food exporters to other countries as well.

For example, precipitation has risen gradually in Iowa over the past century, but can vary widely from year to year. Springs now are wetter, and autumns drier. That can make corn-planting difficult, but dry the grain more quickly in the fall.

Records show a rise in absolute humidity, threatening crops with a higher risk of disease and harmful fungi.

Changing weather patterns also are expected to alter agriculture. Summer storms already can be more intense, and the Midwest has fought to avoid major flooding this year. Models predict more-intense rains, worsening runoff and related pollution and flooding.

Also, warmer winters could mean a greater chance of rain rather than snow. That might help soil moisture.

The records Takle analysed showed Iowa averages five more frost-free days a year than in 1950. But that doesn't mean more time to grow crops, because of changes in temperature and precipitation patterns.

Generally, Iowa now has warmer winters, but fewer extremely hot summer days. Overall, the Midwest is expected to warm through the middle of the century, but not as much as other parts of the country.

The IPCC reports strong research suggesting rising carbon dioxide will make plants grow faster, but adds that the long-term yields would depend on other factors. 'Results of a large number of experiments designed to examine the effects of elevated CO2 concentrations on crops have generally confirmed high confidence in a net beneficial effect of CO2 fertilisation, up to some level,' the panel reports.

'Sustained plant response under field conditions to concentrations beyond 2xCO2 would likely be dependent on species as well as water and nutrient status and is highly uncertain.'

The U.S. Global Change Research Programme made a similar prediction in report last September: 'Many crops show positive responses to elevated carbon dioxide and low levels of warming, but higher levels of warming often negatively affect growth and yields.'

That organisation also reports other potential problems for agriculture, including disruption of the livestock industry. A key issue could be the severity of individual rains.

'Extreme events such as heavy downpours and droughts are likely to reduce crop yields because excesses or deficits of water have negative impacts on plant growth,' the research programme reported.

Another key threat is likely to come from pest species, both plants and insects, spreading into areas that don't currently treat crops with chemicals aimed at those particular invaders.

'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,' the programme's report read.

That phenomenon already is showing up in fields, with farmers in warmer areas spraying more than their counterparts to the north. For example, Florida sweet corn growers spray pesticides 15 to 32 times a year, while New York farmers spray five or fewer times, the research programme reported.

Scientists expect the warming to disrupt a hallmark farming industry: livestock production. 'Increased heat, disease, and weather extremes are likely to reduce livestock productivity,' the research programme found.

Part of that problem would come from heat-stressed pastures. 'Forage quality in pastures and rangelands generally declines with increasing carbon-dioxide concentrations because of the effects on plant nitrogen and protein content, reducing the land's ability to supply adequate livestock feed.'

Not only does warming open the possibility of new pests in a given area - those that migrate northwardly, for example - but also will change the distribution of fish and other wildlife.

The Marine Biological Laboratory based in Woods Hole, Massachusetts, has already reported changes in water circulation and fish species distribution in the Arctic zone off Canada. Takle said some wildlife biologists have watched for similar behaviours in the Mississippi River.

*This story is part of a series of features on biodiversity by Inter Press Service (IPS), CGIAR/Biodiversity International, International Federation of Environmental Journalists (IFEJ), United Nations Environment Programme/Convention on Biological Diversity - members of the Alliance of Communicators for Sustainable Development (COM+ - www.complusalliance.org).

© Inter Press Service (2010) — All Rights Reserved. Original source: Inter Press Service

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