A growing problem

Conventional agriculture—a vicious cycle

conventional produce
Courtesy morguefile


By Kelle Kersten

Current agricultural production and distribution systems have contributed to the increase of greenhouse gases and subsequent global warming. In turn, the rise in temperatures is beginning to affect our agricultural crops, and if this rise continues unchecked, our food supply will be threatened. 

As reflected on the National Arbor Day Foundation’s revised hardiness zone maps, temperatures in many areas of the country have warmed considerably since the last USDA hardiness zone map was published in 1990.  Significant portions of many states have shifted at least one full hardiness zone, and some areas of the country have warmed two full zones.

Temperatures in the Northeast have increased an average of 4.3 degrees over the last 30 years, and as a result, plants are changing their patterns. Apple trees and grapevines are blooming about eight days earlier, which increases the risk of frost damage to the flowers and developing fruit if there is a sudden cold spell in the spring. According to David Wolfe, professor of horticulture at Cornell University, apple trees need a winter chilling period of at least 30 consecutive days with temperatures below 40 degrees. Any winter thaws that interrupt the chilling period inhibit fruit production. Increases in summer temperatures are also detrimental to food plants, because higher temperatures during pollination can cause a loss of pollen viability, resulting in male sterility of many plant species such as oats and tomatoes.

Because the geographical range of many fruit and other food crop species may shift northward due to changes in hardiness zones, chilling period, and pollination, agriculture in California, where half of the nation’s fruits and vegetables are currently grown, may be drastically impacted. If average statewide temperatures rise more than eight degrees, the chilling requirements for some high-value fruit crops such as almonds, cherries, and apricots may not be met and these crops could no longer be produced there. Higher temperatures will also increase crop demand for water at the same time that water supplies will be diminishing due to declining snowpack in areas where much of the water supply comes from melting snow and ice in the mountains.

Another likely effect from global warming is an increase in agricultural insects, diseases, and weeds.  A recent study from the University of Washington suggests bugs could boom because, as biologist Ray Huey explains, many insect species will be able to adapt to hotter temperatures and reproduce faster.  Both bad and beneficial bugs could have population explosions and these warm-weather bugs will be more voracious eaters than cold-weather bugs.  A 5.5 degree increase in temperature could mean the difference between aphids that produce 300,000 offspring in two months to those that produce more than a million.

Warmer temperatures are also responsible for overwintering of bugs, keeping them alive through the winter and adding to the increase in agricultural pests.  Tom Wickham of Wickham’s Fruit Farm in Cutchogue, NY, recalls that apple scab used to die off during a really cold winter of zero degrees. However, his area, which used to have winters with temperatures well below zero, is now significantly warmer.

Weeds like poison ivy, ragweed, and Japanese honeysuckle also thrive with higher temperatures and increased carbon dioxide. Ragweed produces ten times the amount of pollen under these conditions.  In addition, weeds are becoming more resistant to herbicides.  Canada thistle, for instance, requires three times the regular amount of herbicide in the presence of higher carbon dioxide. 

An estimated 20% of potential food crop production is already lost each year due to unfavorable weather patterns such as drought, flood, severe heat and cold, and strong storms. This percentage will increase significantly if, as predicted, global warming generates more extreme weather events such as earlier and more intense hurricanes and torrential downpours with periods of drought in between.

Fortunately, there is a solution. As Rodale CEO, Tim LaSalle reports organic farming practices that build soil pull carbon dioxide from the air and lock it in soil as carbon, which benefits agriculture and the environment in many ways. This is in sharp contrast to conventional agricultural systems that use tillage and apply soluble nitrogen fertilizers that send carbon into the atmosphere instead of retaining it in the soil as organic systems do.

If applied to all U.S. cropland, these practices could mitigate 25 percent of the U.S. emissions from fossil fuel combustion.

Kelle Kersten is the Chapter’s sustainable agriculture committee chair.  

Published March 2007