Published: March 31, 2009 10:03 am      

Global warming and ag

This is the first of a two-part series to look at the science surrounding global warming and the potential impacts and opportunities for the agriculture industry in the Midwest. The Earth has been going through periods of natural warming and cooling for thousands of years. The major question in the science community is what impact the expected future increase in greenhouse gases will have on future atmospheric temperatures.

There are five climate change factors contributing to changes in long-term average global temperatures. Two of those factors are naturally occurring while three are “anthropogenic” factors, caused by human activity on earth.

The natural factors

— Solar: The absorption of solar energy heats up the atmosphere and allows for life on Earth. Variations in sunspot activity changes the intensity of solar radiation reaching the Earth, which ultimately affects atmospheric temperatures.

— Volcanic: Volcanoes temporarily cool the Earth, and there has been a decrease in volcanic activity in the past 100 years, leading to more natural warming of the atmosphere.

The human factors

— Greenhouse Gases: The two main greenhouse gases are carbon dioxide and methane; however, there are many other gases that may impact the Earth’s atmosphere. As these gases build up in the Earth’s atmosphere, they absorb heat and keep it in lower atmosphere, rather than allowing a more natural exit of the heat energy.

— Ozone: Ozone is a gaseous atmospheric component created from human activity that filters potentially damaging ultraviolet rays from reaching the Earth’s surface. Changes in that Ozone layer can lead to modest modifications in atmospheric temperatures.

— Sulfate: Sulfates are microscopic particles (aerosols) that increase the acidity of the Earth’s atmosphere in form of “acid rain,” which can lead to environmental challenges; however, an increase of sulfate particles may actually reduce the impacts of global warming.

The major concern related to global warming is the build-up of the greenhouse gases. Practices such as burning fossil fuels and changing global land-use patterns can increase carbon dioxide emissions, and lead to increased heating of the atmosphere. Carbon dioxide is a concern due to the large amounts that regularly released into the atmosphere. Water vapor is the most prevalent greenhouse gas; however it does not remain in the atmosphere very long. Some of the other gases have a much lower occurrence than water vapor, but are much more powerful and stay in the atmosphere much longer. For example methane has a 21 times greater warming effect on the Earth’s atmosphere that carbon dioxide, while nitrous oxide has an almost 300 times greater effect on heating the atmosphere compared to carbon dioxide.

Shifts in weather patterns due to global warming are likely to be fairly gradual, which make it hard to differentiate the whether climate changes are from natural factors, or related to human activity.

Based on an Iowa State University analysis of the 2007 report by the International Panel on Climate Change and a 2008 assessment report from the U.S. Climate Change Science Program, the following potential impacts were identified for future climate trends, which could impact the Midwestern agriculture industry:

Temperature-related changes:

— Longer frost-free periods.

— Higher average winter temperatures, both maximum and minimum.

— Fewer extremely cold temperatures in winter, and very high temperatures in summer.

— Higher nighttime temperatures in winter and summer.

— Increased temperature variability.

— More freeze/thaw cycles



Precipitation-related changes:

— Increase in average annual precipitation; however, much more variability in precipitation.

— Biggest increase in precipitation will be late winter and early in the growing season.

— Greater soil moisture recharge, but more incidence of water-logged fields.

— Higher absolute humidity, and higher incidence of severe storms.

— More intense rain events, with potential for flooding and severe runoff.

— Longer periods without rain, especially later in the growing season.



Other Possible Climate-related Changes :

— Faster plant growth and maturity, and plants with increased water-use efficiency.

— Emergence of new and faster-growing weed species that are more difficult to control.

— Conditions more favorable for the development of plant diseases.

Some of these trends have already been ongoing for several years, and some trends are likely to intensify in the coming years. For example, average nighttime temperatures in Iowa have been rising for the past 30 years, while average maximum summertime temperatures have been declining. Total annual and growing season precipitation in the Midwest has also increased slightly in recent decades.

The trends listed earlier will present a mixed bag for future crop production in the Midwest. Some of the trends, such as warmer early spring temperatures, longer growing seasons, and greater soil moisture recharge may be beneficial to future crop production. However, wider variations in weather patterns, more severe storms, and potential increased weed and disease pressure could present future challenges to crop producers.

In the next issue we will look at challenges and opportunities for the agriculture industry, as measures are enacted in the United States and throughout the world to address the concern over global warming. We will also focus on bio-fuels, as related to future global warming policy and management.



Kent Thiesse is farm management analyst and vice president at MinnStar Bank, Lake Crystal. 507-381-7960; kent.thiesse@minnstarbank.com