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Climate Change Tied to Crop Losses, Increases in Pest Populations

(Beyond Pesticides, March 19, 2007) Stanford University and Lawrence Livermore National Laboratory researchers are publishing a study saying that some of the world’s farms are yielding markedly fewer crops because of global warming, according to the San Jose Mercury News. Meanwhile, providing further evidence that the pace of global warming is accelerating, scientists announced last week that this winter was the hottest on record – and that surface temperatures around the world have been increasing at three times the rate they were before 1976.

This warming most likely is costing the planet $5 billion annually in losses to three of the six major food crops, the Stanford and Lawrence Livermore researchers say. The study warns that wheat, corn and barley are especially affected, with 40 million fewer metric tons of the crops produced each year. For every 1 degree increase in temperature, the researchers say, crop yields drop by about 3 percent to 5 percent, and the decline is clearly caused by human activity.

“Global warming is having real impacts – and we’re seeing their effects already,” said Chris Field, one of the authors of the crop study, and director of the department of global ecology at Stanford’s Carnegie Institution.

“This is a sign we’re going to have more of this [crop loss] in the future,” said Kevin Trenberth, head of the climate analysis section at the National Center for Atmospheric Research in Boulder, Colorado. “This will have an impact on many things that will affect humans, from food and crops but also on all kinds of ecosystems, wildlife, forests, even fisheries and especially things like wildfires, things that can be really devastating.”

It isn’t entirely clear exactly how warmer temperatures are driving the crop changes. One theory is that without occasional deep freezes, insects and plant diseases aren’t killed off during the winter, allowing them to continue to wreak havoc. Drought also can play a role. As climate scientists analyze the effects of the warming that’s already been occurring, they say they believe it’s only going to get worse.

The effects on crops are just the beginning of the widespread effects that global warming will have on pesticide-related issues. Global warming will increase pest populations, including weeds, invasive species, insects, and insect-borne diseases, which will likely lead to large increases in the use of pesticides. The effects of climate change are already beginning to be seen, and will continue to be seen for years to come. Without drastic actions to curb global warming, the current course we are heading on will lead to booms in pest populations and pesticide use. Pesticide use is tied to its own myriad of problems, including pest resistance, interference with ecological services, such as beneficial organisms, water quality issues, endocrine disruption, immune suppression, and other health and environmental issues.

Below is a summary of some of the research linking global warming to increases in pest populations:


Fast-growing weeds are able to adapt and change reproductive patterns as quickly as over a 7-year period, an ability which will lead to their expansion in response to global warming. According to a new study by researchers at the University of California, Irvine, those plants with short life cycles can adapt more quickly to change than those that reproduce slowly.(1) In their study, they found that the annual plant Brassica rapa, or field mustard, flowered significantly earlier than usual during a period a drought. Droughts, which are expected to become more frequent, especially in arid regions, cause abbreviated growing seasons. The ability of Brassica rapa to adapt in just a few generations shows how weeds will likely keep up with any attempts to develop crops that can adapt to global warming.(2) The findings are reported in the January 16, 2007, issue of the scientific journal Proceedings of the National Academy of Sciences.

Another study finds that increased levels of atmospheric carbon dioxide cause poison ivy to grow larger and more poisonous.(3) An additional expected result of rising carbon dioxide levels is an increase in invasive plants. One study finds that in plant communities, high levels of carbon dioxide stimulate the growth of invasive plant species more than native species.(4) Additionally, as carbon dioxide increases, herbicides may become less effective at controlling invasive weeds.(5)

Insect populations

In addition to increasing weed populations, global climate change is expected to increase the frequency and the intensity of insect outbreaks through direct effects of climate change on insect populations, as well as through disruption of community interactions.

Researchers at the University of Washington have found that insect species that adapt to warmer climates also will increase their maximum rates of population growth, meaning that global warming will likely lead to increased insect populations. The study’s authors say that this “warmer is better�? phenomenon is likely to have widespread effects on agriculture, public health and conservation.(6)

Additionally, climate change is expected to increase the range of some insect pest populations. For example, the red imported fire ant, an invasive pest originally from South America that currently occupies much of the Southeast, is expected to expand its range into the eastern U.S. over the next century, with the help of global climate change.(7)

A 2005 study finds a decrease in levels of insect parasitism as climatic variability increases. Specifically, they predict that the decrease in parasitoids, which feed on and ultimately kill herbivores and in this case, caterpillars, will lead to an increase in the frequency and the intensity of herbivore outbreaks as the climate becomes more and more variable. The authors hypothesize that “these indirect effects of climate change via disruption of enemy-herbivore dynamics could be as disruptive as some of the more direct effects of global warming” and could increase “the frequency and perhaps intensity of herbivore outbreaks.” They predict these changes will be most disruptive in agricultural systems.(8) Many species of parasitic wasps have been used as biological controls in agriculture, and climate change may compromise their ability to control pests, leading to increased use of pesticides.(9)

Insect-Borne Disease

With the boom in insect populations, scientists also hypothesize that there will be increases in insect-borne diseases such as malaria, dengue fever, and viral encephalitis. Scientists believe that climate change will increase disease transmission by shifting insects’ geographic range, increasing reproductive and biting rates of the insects, and by shortening the pathogen incubation period.(10) In fact, research shows that malaria zones are already increasing worldwide. It has been suggested that 60% of the world will be in a malaria zone by 2100.

To find out more about the link between pesticides and global warming effects, as well as to learn about ways that organic agriculture can help sequester carbon, join Beyond Pesticides at our 25th National Pesticide Forum, Changing Course in a Changing Climate: Solutions for health and the environment, June 1-3 in Chicago, IL. Details at www.beyondpesticides.org/forum.

TAKE ACTION: Learn about ways to take action on global warming at http://www.climatecrisis.net/takeaction/.

(1) Franks, SJ, S Sim, and AE Weis. 2007. Rapid evolution of flowering time by an annual plant in response to a climate fluctuation.Proceedings of the National Academy of Sciences. Published online before print, 10.1073/pnas.0608379104.

(2) Washington Post. Tuesday, January 9, 2007; Page A09, “Weeds Adapt Quickly To Climate Change.�?

(3) Mohan, J.E., Ziska, L.H., Sicher Jr, R.C., George, K., Thomas, R.B., Schlesinger, W.H. 2006. Poison ivy grows larger and more poisonous at elevated atmospheric CO2. Proceedings of the National Academy of Sciences. 103(24):9086-9089.

(4) Ziska, L.H., George, K. 2004. Rising carbon dioxide and invasive, noxious plants: Potential threats and consequences. World Resource Review. 16:427-447.

(5) Ibid. (Ziska and George 2004).

(6) Frazier, M., R.B. Huey, and D. Berrigan. 2005. Thermodynamics constrains the evolution of insect population growth rates: “warmer is better.” American Naturalist 168:512-520.

(7) Morrison, LW, MD Korzukhin, and SD Porter. 2005. Predicted range expansion of the invasive fire ant, Solenopsis invicta

(8) Stireman, JO, LA Dyer, DH Janzen, et al. 2005. Climatic unpredictability and parasitism of caterpillars: Implications of global warming. Proceedings of the National Academy of Sciences of the United States of America 102:17384-17387.

(9) Ibid (Stireman et al 2005).

(10) J. A. Patz, P. R. Epstein, T. A. Burke and J. M. Balbus. 1996. Global climate change and emerging infectious diseases. JAMA 275(3).


3 Responses to “Climate Change Tied to Crop Losses, Increases in Pest Populations”

  1. 1
    University Update Says:

    Climate Change Tied to Crop Losses, Increases in Pest Populations…

  2. 2
    xtr0uble Says:

    thanks for this article! :)

  3. 3
    forumetki Says:

    Thanks a lot! Great share!.

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