The report â€œGlobal Climate Change Impacts in the United States: A State of Knowledge Report from the U.S. Global Change Research Programâ€, provides some crucial aspects that need to be considered by food producers in the US and globally.
In the following paragraphs, I summarise some key points made in reference to the climate change effects on the US production of fruit and vegetable crops. However, the report also discusses the impacts in US livestock and fisheries.
â€¢ While climate change affects agriculture, the latter also affects climate change. Agriculture contributes 13.5 % of all human-induced greenhouse gas emissions (GHG) globally. In the US, agriculture represents 8.6 % of the nationâ€™s total GHG emissions.
â€¢ Higher temperatures will mean a longer growing season for crops that do well in the heat, such as melon, okra, and sweet potato, but a shorter growing season for crops more suited to cooler conditions, such as potato, lettuce, broccoli, and spinach.
â€¢ Warmer temperatures are likely to affect specialty crops in California, such as apricots, almonds, artichokes, figs, kiwis, olives, and walnuts. These crops (and other not mentioned in the list) require a minimum time of exposure to chilling temperatures during winter to induce a dormant state and be ready for fruit bearing in the next harvest season. However, the length of time where these low temperatures are achieved is already decreasing in California. The worst case scenario for economic losses is 40% for wine and table grapes, almonds, oranges, walnuts and avocados.
â€¢ Higher temperatures also cause plants to use more water to keep cool. But fruits, vegetables and grains can suffer even under well-watered conditions: if temperatures exceed the specific maximum level for pollen viability in a plant, the plant will not produce seed and therefore it will not reproduce.
â€¢ Nighttime temperatures are expected to continue to rise in the future. For example, snap beans show substantial yield reduction when nighttime temperatures exceed 26.7Â°C.
â€¢ Water irrigation is sometimes used to maintain adequate temperature conditions for the growth of cool season plants (such as many vegetables). With increasing competition for freshwater supplies, the water needed for these crops will be limited.
â€¢ Fruits that require long winter chilling periods (e.g.some apple varieties and berries)will experience declines. Cranberries have a particularly high chilling requirement, and there are no known low-chill varieties. It is expected that Massachusetts and New Jersey, which supply about half the US cranberry crop, will be unable to do so.
â€¢ Even crop species that are well-adapted to warmth, such as tomatoes, can have reduced yield or quality when daytime maximum temperatures exceed 32.2Â°C for even short periods during critical reproductive stages.
â€¢ Many insect pests and crop diseases thrive due to warming, increasing losses and necessitating greater pesticide use. Additionally, higher temperatures are known to reduce the effectiveness of certain classes of pesticides. Pesticide spraying will be needed more frequently or in higher doses.
â€¢ Predicting the optimum planting date for maximum profits will be more challenging under increased climate uncertainty. This uncertainty applies for both local production and supply from competing regions.
The report also suggests some strategies for adaptation, presented below:
â€¢ Adaptation strategies for agriculture include more efficient irrigation, shifts in cropping patterns and the use of groundwater. In particular, changing planting dates can be an effective no- or low-cost option for taking advantage of a longer growing season or avoiding crop exposure to high temperature stress or low rainfall periods. Effectiveness will depend on the region, crop, and the rate and amount of warming.
â€¢ Another adaptation strategy is changing to crop varieties with improved tolerance to heat or drought, or those that are adapted to take advantage of a longer growing season. This is less likely to be cost-effective for perennial crops, for which changing varieties is extremely expensive and new plantings take several years to reach maximum productivity.
â€¢ Even for annual crops, changing varieties is not always a low-cost option. Planting stress-tolerant varieties often requires new farming equipment or a wide range of adjustments. In some cases, it is difficult to breed for genetic tolerance to elevated temperature or to identify an alternative variety that is adapted to the new climate and to local soils, practices, and market demands.
The report has abundant scientific references backing each of their claims. For those interested in these, I recommend to go straight to the source:
Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson, (eds.). Cambridge University Press, 2009.