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If climate should change in the future, how vulnerable is agriculture? What are some of the potential impacts? |
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| Jeff Andresen, Agicultural Meteorologist, Michigan State University | |
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Direct impacts of climate change on agriculture that we all need to be concerned about:
How can growers and farmers adapt to a changing climate? One way would be to add water. Water is the single most important variable in our production systems. If irrigation is increased and the precipitation recharge rates change we could have problems with the amount of water in the aquifer. There could be changes in nonagricultural water usage also. Climate History Data Here is a graph depicting the latter part of the 19th century, "Annual Global Surface Mean Temperature Anomalies" from the National Climatic Data Center. From 1880 through 2001, we have 3 different sets of surface temperature, which are the best guess we have as to annual mean temperature around the entire world. Integrating all the values that we have, we can see a couple of moves here: the zero line is the long-term chart data the normal for the whole period. For the first 40 years or so, up until the 1920´s or 30´s most of these annual temperatures were below long-term mean. We went above the long term mean from 1910 to 1940 then had a stabilization, even a little bit of a decline up until the 1970´s. Since roughly 1980 to the present we´ve had a fairly significant increase overall about 3/4 of a degree Fahrenheit. In terms of global integration, that is a very large value. There are some climatologists who think that this increase is beyond the limits of what we would see with natural variability. It is very difficult to separate the signal of any change in climate from the natural variability of the noise of the system. Some climatologists believe that this is beyond what would normally be encountered. It has warmed up within our region, also. The "Mean Annual Observed Temperatures Regional Average" graph from our Regional Assessment, shows the temperatures within our region and averages them together for the three states from 1895 to 1996. There is some similarity, but not the same magnitude of increase. Most of the temperatures that we do see on an annual basis are within bounds that we´ve seen during the hundred or so years. The major move, climatologically speaking, in the Great Lakes region is not temperature at all, but precipitation. The "Total Annual Observed Precipitation Regional Average, 1895-1996" data shows that beginning in the 1920´s to 1930´s we´ve had a steady, but consistent increase in the amount of rainfall over our area. In some parts of our region, Wisconsin and much of the lower peninsula of Michigan, this is even more pronounced. The largest, most significant move we can see in any of our long-term chronological records; it´s becoming wetter in our part of the world. If it is becoming wetter, it is becoming cloudier as well. The "Daily Solar Radiation vs. Year, 1961-1990" values reflect that if we have more days with precipitation, that we probably will have more clouds as well. We have more days with precipitation and more wet days successively. This increase in wetness is across all seasons. One trend in temperature that Professor Jay Harman and I observed in our work is the spring warm up in our region, especially in Michigan, appears to be occurring earlier than in prior decades. This is evident in a time trace of 150 growing degree day units and 300 growing degree day units started from the beginning of the year. Another piece of evidence that supports this is that the ice cover on the Great Lakes also appears to be less than it was decades ago and the break up of ice when it does occur has occurred earlier. All of these may be linked in our climate. Spring appears to be coming earlier and it´s warmer. To determine what the most important climatological variable is for crop yield, in this case, corn, the Great Lakes Regional Assessment compared water stress and amount of warmth in a given growing season in relation to crop yields. The data showed that for the southern part of our region, which is closer to the main production of the Corn Belt, water is key. (Dry land agriculture was used for the study, no water added.) In the northern part of our region, temperature becomes just as important of a limitation. Historical trends from our analysis—data for soybeans, alfalfa and corn indicates positive trends in yield with all other variables held constant, except weather. Technology and all other factors are held constant with crop simulation models. Amount of water that the crop uses from soil storage has been decreasing due to increased precipitation. In summary, as it´s become wetter, conditions have generally become more favorable for crops. What about the future? There are a number of groups around the world that use sophisticated, deterministic climate models to try to predict where we might be in 10, 20 or 100 years into the future. While there are differences among them for regional size areas, the majority in our area, suggest that the climate will be warmer and wetter in the future given increases in CO2 and other greenhouse type gases. There is a large amount of variability, but the general trend is fairly consistent. Especially for temperature, a little less so for precipitation. The reason the Climate Change Assessment was broken into regional areas is due to the fact that changes in these areas can be very different. Projected agricultural productivity changes as a function of region, assuming a warmer and wetter climate for much of the U.S. in one climate change scenario shows:
On an international level, we tend to see a trend in gains in productivity in temperate and cooler, high latitude parts of the world and agricultural losses in productivity in the tropical areas. Some of the tropical areas would be least able to deal with losses in productivity. A recent study, “Estimated changes in national crop production in 2030 relative to 2000” compares projected yields of dry land, and irrigated crops of corn, soybeans, soft wheat and potatoes, and projected water usage—if you look over the entire country what you see is a lot of plusses. If we take the sum of the entire system, we have losses in some places, gains in others. Note that some of this is due to carbon dioxide enrichment. If you take that factor out, the gains may actually turn to losses. Carbon dioxide enrichment is very important. Note that irrigation water uses does not change greatly except for corn. Corn has a huge variability probably due to economic factors as well. Three crops, alfalfa, maize, and soybeans, were studied specifically for ratios of projected future yields compared to yields in the past for the Great Lakes region. Two different climate models were used for this analysis. It is important to note here, that rather we consider CO2, or not, there are very significant increases in productivity projected for these three crops, especially for soybeans and alfalfa. Some plants will benefit to a greater extent due to increased CO2, than others. As CO2 concentrations increase, the efficiency by which the plant uses water and its loss through transpiration decreases. Increase in CO2 is very beneficial, at least in the lab and in experimentation. There is still debate about if it works long term or not. Given the fact that these are all above 1, this actually suggests in this study that the majority of any increases in the future probably would be associated with CO2 enrichment, besides a warmer and wetter, more favorable climate. Simulated historical and projected soybean yields by decade, in a model from the U.K., with CO2 enrichment included in a station in Southern Minnesota indicate a fairly steady increase. There is quite a bit of variability. Not all of these were increases. Here is a projection for corn in Madison, Wisconsin and in this particular case—a warmer model from Canada—had a drop off in yield and this was much less variable. One very important part of this research is that it has helped us to understand what the basic building blocks of the production system are in terms of the natural system. There is precipitation coming into the system that has to be balanced by the water going out, evapotranspiration, runoff, and drainage. In Michigan, we receive between 12-16 inches of water during the growing season, but we lose approximately 18-20 inches in evapotranspiration. Where does the extra water come from? It´s in the soil. Four to six inches in this soil in east-central lower Michigan, has to come from groundwater storage. What this has shown us is that in the future with a warmer, wetter climate the amount that comes out of storage decreases thereby decreasing the risk to the crop. What are the agricultural strategies for coping with climate change? Learn to live with it, adapt; or try to solve the problem through mitigation. For agriculture there are a number of options for mitigation:
A study of double cropping of soybeans following wheat was conducted. (This was suggested by a very astute agent, a professional in the field who asked, "What about double-cropping here in Michigan?" Traditionally this practice doesn´t exist in Michigan, it´s done in the Ohio Valley and areas to our south.) In this particular project we wanted to look for an adaptation, how viable is this. For this simulation, 15 bushels or so, to break even. The odds of getting close to that break even are very low. The real key to this was water. The wheat takes most of the water out of the profile and if you add water through irrigation, you dramatically change the rate of success (at least in the model.) Hopefully, this can be taken out to the field and we can actually start to experiment with this. If anyone asked you about irrigating soybeans, you´d say, "It doesn´t pay." In this case, maybe it might. Summary Weather and climate are among the most uncontrollable variables in agricultural production systems. Over the past 50 years, climate here has become wetter. There have been more wet days, it has been cloudier. The single most important variable for most of our crop systems continues to be water, even as it is getting wetter. This should result in a positive trend over time. If the world does become warmer and wetter, as suggested by GCM projections for the future, at least the initial guesses here are, that for many crops this would be beneficial. A significant portion of any future yield increases will be associated with CO2 enrichment. Recent research results suggest greater agronomic potential for northern sections of the Great Lakes Region, even in areas with less suitable soils. More research is needed especially with regard to narrowing down the climate models themselves and the indirect effects of climate change such as disease and insect problems. |
