1. Efforts to better quantify and reduce uncertainties related to processes already represented in crop models are perhaps the most critical need for anticipating effects on food availability. A primary means for achieving this will be more experimental studies that manipulate temperature, CO2, soil moisture, and ozone, both separately and in combination, and for a range of crops of importance to the food insecure. The experiments will be particularly useful in tropical systems where they have been essentially non-existent in the past. A second important approach will be to continue to test existing ecophysiological models with observations of yield and weather variations, at scales ranging from individual fields to entire regions. These same observations should also be used in time-series and panel-based analyses.
2. More effort is also needed to quantify and reduce uncertainties in future climate. No longer should studies use output from just one or two climate models, as projections of 20+ GCMs are now commonly available. Improvements in down-scaling techniques will also be of use, although in our view the importance of such efforts is often overestimated, given that downscaling is most critical for rainfall whereas the consequences of rainfall trends will be relatively small compared to warming in many places.
3. Much work is needed to assess the reliability of water resources in irrigated areas, a factor that is just beginning to be considered in tandem with direct yield effects. Similarly, the effects of higher ozone, weeds, pests and pathogens, and sea level rise on crop productivity remain largely unknown and deserving of more quantitative scrutiny. Adding complexity to models should not, in and of itself, be a goal of future research, and in many cases it is unlikely that these factors will significantly change results. Instead, we should seek to identify the domain over which current models are inadequate, and identify not only the key factors needed in those instances but also the size of that domain. Too often a model that fails (or succeeds) in modeling one particular location and set of conditions is dismissed (or applied) in all other situations.
4. There are numerous questions about how fast and effective adaptation measures will be. At the farm level, these include how well farmers' can perceive climate trends amidst substantial variability, how well they understand the response of their crops to these trends, how quickly they can learn and implement new technologies, and what are the risks and likelihood of success for these adaptations. All of these should be amenable to some evaluation, particularly using data from the most recent decade in regions that have been warming most rapidly. There are also important questions about the scope for technology development, and more communication between the crop modeling and crop improvement communities appears particularly worthwhile. Yet often the impacts of future technologies are difficult to anticipate in advance (if we knew what the technologies would be, we'd already have them!)
5. Surprisingly little has been done to evaluate the true scope of cropland expansion in colder regions. All trade models include some component of cropland expansion, and often this is a critical relief valve for price pressures. But how suitable will the soils in these zones really be for crop production, and how quickly will expansion take place? Again, evidence from recent decades, such as the expansion of wheat in Northern China, should help to better understand these dynamics.
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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.