- Marty from Wheaton -
John Upton over at Grist.org has a straightforward review of the issue, but I will give you the highlights from his work and some of my own research. First of all, global temperatures are increasing, at at approximately the rate predicted by climate scientists in the later part of last century.
Increases in ambient temperature change evaporation rates. If we remember about the water cycle from grammar school, that evaporation creates the storm clouds that eventually produce rain. The thing about higher ambient temperature air is that it holds more moisture than lower temperature air. (It's why you feel "clammy" when the temperature quickly drops from 85F to 75F if it doesn't rain...the same amount of moisture is in the air, but it can't hold onto it. As air cools, the gas molecules move closer together, leaving less room for the water vapor molecules. The opposite happens as temperatures climb.) This increased moisture capacity sucks up more moisture from the ground, holds onto it longer, and then dumps it quickly in the form of more torrential rain. The ground experiences less frequent rain, causing it to dry out, making it harder to absorb the more torrential rain.
This disruption to the regular water cycle also affects the recharge rate of local water sources...and for our nations prime growing areas, that means the Ogallala Aquifer. As rain falls less frequently in the areas served by the aquifer, the levels within it drop, and as we withdraw more water from the aquifer for air conditioning, human consumption, and lawn watering, we leave less for irrigation. This combination of rainfall reduction and increased human withdrawal leaves less water than necessary for growing crops.
As the Upton article points out, over the past half century, we have moved to more genetically modified "mono crops" which have a number of issues, but one of them is the combined lack of resilience to weather variation. Whereas in previous times of significant draught, farmers could count on the variety of crops to help balance out yields, that opportunity no longer exists, and the science of genetic modification has not kept up.
Although that provides a theoretical explanation, in the tropics, they have already experienced some of these crop yield reductions due to increases in temperature.
The charts from the Intergovernmental Panel on Climate Change report (as summarized by Easterling, W. and Apps, M. in "Assessing the Consequences of Climate Change for Food and Forest Resources: A View from the IPCC", 2005) show that in areas that have experienced temperature increases, that crop yields drop with each step of temperature increase. If we continue on this path, we can expect similar changes to our growing patterns.
As for the changes in pricing, this year we can expect a small increase, but most agriculture is purchased on futures markets with prices set well ahead of time. The real impact will be next year when buyers will price the volatility into the marketplace. As the market expects to sell less corn and soy next year, it will demand higher prices assuming that buyers will want to consume just as much of the product.
The solutions to this spiral are not easy. On one level, we need to stabilize climate disruptions in order to take away the driving force. However, that will not reduce the temperature gains already made, so a combination of water efficiency and alternative growing methods will help to extend yields and increase crop resilience. It will be interesting to see if any long term reduction in yields changes national or regional policy. We currently subsidize ethanol (gas additive produced from agriculture) and food additives in order to provide a larger market for corn and soy. With lower yields, we could stabilize prices by lowering these subsidies and decreasing demand. When ethanol received a boost in the early 2000s, the competing interests for corn increased prices across the food industry. A "double whammy" could completely change the food market.
A final option from my point of view (among many possible adaptations we can make) comes from reducing energy usage in tandem with water usage. I have already written on the subject of decreasing water use per capita in our culture (here and here), including the impact of water for energy production. For each unit of electricity consumption we reduce, we also reduce water needed to produce that electricity. A combination of all of these solutions (plus many others) will be needed to solve this vexing problem
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