A second possible farmer adaptation to climate change is to switch varieties or crops to something better suited to the new climates they face. A farmer currently growing maize might switch to a faster-maturing maize variety if drought becomes more common, or might choose to grow a potentially more drought-tolerant crop like sorghum. But such decisions will not be made on the basis of climate alone. Different varieties and crops have different input requirements and costs associated with their production, different responsiveness to local stressors and can face very different output prices in ways that affect their profitability. To the extent that climate change affects the relative profitability of different crops and varieties in ways apparent to farmers - and in ways they can respond easily to - crop or variety switching could constitute a fruitful adaptation strategy.
In the case of switching varieties, climate change suggests two primary adaptation alternatives, the choice of which depends on whether moisture or heat is expected to be limiting. In low-rainfall areas where moisture stress is expected to remain a primary constraint on plant growth, a promising adaptation might be to plant faster-maturing varieties that avoid drought or heat stress during sensitive stages of plant growth, such as flowering or grain filling. Developing faster-maturing varieties for areas with short and variably rainy seasons (i.e. much of Africa) is a common goal of many breeding programs, and such a strategy would seem promising anywhere climate change is expected to shorten growing seasons.
In areas where moisture regimes exhibit little change, however, a move in the opposite direction toward longer maturing varieties might be preferred, because warmer temperatures tend to speed development and lower yields (Chapter 4). Longer maturing varieties would thus be required to maintain the length of time for total crop development as temperatures warm. Simulation studies indicate some benefits for this strategy. For instance, Tubiello et al. (2002) find that switching to longer-maturing winter wheat varieties at a site with plentiful moisture fully offsets the 15% projected yield losses under climate change, but find somewhat smaller gains for more arid areas.
Beyond shifting among varieties, farmers could also switch what crops they grow as the climate changes. As with choice of variety, farmers' choices about what crops to grow depend only partly on climate, and year-to-year crop choice decisions are likely dictated much more by expected prices at harvest than by climate concerns. For instance, farmers in the Midwestern US readily shift area between maize and soybeans depending on market signals. Nevertheless, over the long run climate exerts clear influence on crop choice. Climate clearly explains much of why rice is grown in the warm wet climates of Southeast Asia and wheat in the cooler, drier northern temperate latitudes of North America and Europe, and not the reverse. Similarly, the highly variable climates of much of Africa induce poor risk-averse farmers to grow lower-value but drought-tolerant crops such as cassava.
If climate matters to crop choice, then farmers could plausibly gain by switching crops if new climates favor a different crop over the one currently grown. This is the basic thrust of the so-called "Ricardian" estimates of climate change impacts on agriculture (Chapter 6). Instead of determining the potential impacts of climate change on the yield of a specific crop, as many studies do, these studies seek to isolate the effect of mean climate on land values in a given region, while controlling for other factors beyond climate that might affect land value (slope, soil type, etc.). The argument is that with well functioning markets, the value of land should reflect the current and (discounted) future stream of profits that can be made from using the land - whether it be used to grow corn or wheat or golf courses. The estimated effect of climate on land values should then in theory reflect all of the crop-switching adaptations farmers could make over the long run (Mendelsohn et al. 1994).
Consistent with the argument that the land values approach offers more thorough picture of farmer adaptation, estimated impacts of climate change are often more positive/less negative in these studies than in other studies that focus on single crops (e.g., Cline 2007, Chapter 5). But this method of modeling adaptation is not without its significant critics, who point out among other things that such methods might overstate the choice set that each individual farmer might have (Hanemann 2000), and thus overstate potential gains from adaptation.
More broadly, there are various factors that might constrain a farmer's ability or willingness to switch varieties or crops, such as the limited availability of alternatives, or the costs or perceived risks associated with adopting a new crop or variety. For instance, seed systems throughout much of Africa are poorly developed, such that locally adapted varieties of different maturity lengths or resistance to various abiotic stresses are not always available - and where they are developed, poor, risk averse farmers are often slow to adopt new technologies. Further, farming systems and local consumer taste preferences are often strongly intertwined, likely inhibiting rapid switching among crops. Finally, in countries with recurrent droughts but where temperatures will warm significantly under climate change (i.e. most of Africa), the optimal variety choice might be far from apparent: choose a shorter-maturing variety that avoids big losses in very dry years, or a longer-maturing variety that might maintain average yields as the climate warms?
These constraints are typically not captured in simulation studies of farmer adaptation, such as those using crop models, but can be picked up in some statistical approaches (Chapter 6). The limited evidence available from these approaches suggests that even in rich countries the potential for farmer adaptation within crops could be limited. For instance, using county-level data on US rainfed corn yields, Fisher et al. (2007) show that the estimated effect of temperature on yields is nearly equivalent whether you look at short run yield responses to variability (where little adaptation would be possible) or responses of yield to longer-run climate averages (under which farmers would have had time to adapt). This suggests that, at least under the range of existing technology and management, switching corn varieties would do little to stem the harmful effects of rising temperatures (see Chapter 6).
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.