Example of Indirect Impacts of Climate Change

Much of what has been talked about are direct impacts of climate change in agriculture. As it gets warmer we have increased rate of development, CO2 enrichment adds to increased dry matter production and decreases in transpiration.

Indirect impacts may be just as important as direct impacts. These include insects, diseases and weeds. Farmers and growers do battle with these on a season-by-season basis. If it is a more favorable environment for the crop itself, it´s probably more favorable for weeds also. These factors play an important role in the system.

There has been much less research done on this part of the equation.

One project involving potatoes and the late blight disease (which is a disease the potato industry spends a great deal of money to guard against because it takes a great deal of a crop in a very short time) detected a discernable trend in disease pressure in our region. The disease is caused by a combination of warm temperatures and wetness on the leaves. Combined these cause a higher incidence of leaf blight. If you look at the last several decades show a trend in the variables that are linked to this disease. In particular the dew point temperature (indicates the quantity of water vapor is in the air at a given time) has shown a gradual slope, a discernable increase. The air temperature has shown very minor increases during the growing season. The real trend is in the amount of water in the air. We dont have a good idea of why that is, but the combination means more disease risk over time, with everything else held constant, just due to more moisture in the air.

In a warmer, wetter world, disease would be a major concern in producing a salable crop.

An example of insect pressure in apples is coddling moth damage. (The tolerance for their damage is very low.) In this study the model of the life and development of the coddling moth showed that normally in the Past century weve had either 2 or 3 generations of the insect during the growing season. So the grower would have to take care of each of those generations if the fruit were vulnerable. Here the simulated projected data for the future, if temperatures were 5-6 °F warmer, shows that there is an increase in 2 generations of the insect to 3 generations in the future. There is a whole extra generation of coddling moth to worry about. In terms of control, we go from 4 control sprays to 6. Two points that complicate the system are the cost of the spray and the fact that one of these generations in the simulations occurred very close to harvest. There are pre-harvest requirements for use of the control spray. The grower would have some major decisions to make because he cant apply the chemical, because the fruit is too close to being sold. There may need to be other technology, other compounds used in this case.

This is an example of indirect impacts that can cause just as many or more headaches than can CO2 enrichment or the more vigorous plant because of warmer, wetter conditions.

These areas are where a lot of research needs to be done. This is a large part that we dont understand yet. Well need more studies over the next decade or two to add more realism to these types of assessments. We need to look at quality and these indirect impacts, instead of just whether yield goes up or down.

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