Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 12:56 AM GMT on December 10, 2011
I'm wrapping up my stay in San Francisco for the annual Fall Meeting of the American Geophysical Union (AGU), the world's largest gathering of Earth Scientists. Over eighteen thousand scientists from all over the world, including most of the world's top climate scientists, were in town this week to exchange ideas to advance the cause of Earth Science. It's been a great opportunity to learn about climate change topics I don't know much about, and I attended a fascinating (and somewhat unnerving) lecture on how global warming is expected to affect insects, titled "The Impact of Global Warming on global crop yields due to changes in pest pressure". Global warming is expected to bring a variety of impacts to agriculture, both positive and negative. Extra CO2 in the atmosphere will tend to increase crop yields, but crop losses due to insect pests are expected to double by 2100, according to a insect pest/crop model designed by David Battisti of the University of Washington. These losses will occur in addition to the expected 35 - 40% decrease in crop yields due to higher temperatures by the end of the century.
When temperature increases, the metabolic rate of insects goes up, requiring that they eat more to survive. In the mid-latitudes, the predicted 2 - 4°C temperature increase by 2100 will require insects to eat double what they do now, in order to survive. The increase in temperature is also expected to enable insect populations to rise by 20%. However, insect populations will fall by 20% in the tropics, where insects have evolved to tolerate a much narrower range of temperatures. Let's look at the world's three most important crops: rice, wheat, and corn. In the four largest rice producing countries--China, India, Bangladesh, and Thailand--Insects currently cause a loss of 10- 20% of the crop, and this is expected to double to 20 - 30% by 2100. These nations have 40% of the world's population, and make 60% of the world's rice. For corn, the world's four largest producers--the U.S., China, France, and Argentina--are expected to see insect pest losses double from 6% to 12%. The story is similar for wheat; pest losses are expected to double from 10% to 20% by 2100. The total increased damage to global agriculture is predicted to be $30 - $50 billion per year by 2100. This will likely contribute greatly to food costs and potential food shortages. The model made a number of simplifications that could greatly change this outcome, though. The model assumed that there would be no change to the number of insects that survive winter, and this number is likely to increase in a warmer climate. Precipitation was not changed to reflect what is expected to happen in a changed climate, and this will cause increases in crop yields in some areas, and decreases in others. Farmers are likely to change growing practices and utilize new pesticides to combat the expected increase in pests, and this was not considered, either. It is interesting to note that during the great natural global warming event of 55 million years ago--the Palecene-Eocene Thermal Maximum (PETM)--fossil records of plant leaves show greatly increased levels of damage from insects, supporting the idea that a warmer climate will drive an explosion in the insect population.
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