Climate Change and Agriculture in the United States: Effects and Adaptation

USDA Technical Feb 2013

This could well be the most important US government report ever and yet few Americans will know about it.

This is because the US government has not warned the American public of the reports dire implications for US food production over the next few decades, and far worse beyond. ​​ ​​

Top key message. ​​​Projections for crops and livestock production systems reveal that climate change effects over the next 25 years will be mixed. The continued degree of change in the climate by midcentury and beyond is expected to have overall detrimental effects on most crops and livestock.

The USDA predicts that there will be some losses of some crops from now on. Many US food producing regions have already suffered extraordinary losses from heat waves, drought and floods, and as the US temperatures increase so will such losses.  ​The USDA assumes resilience by the US farmers will make up for such losses, but the evidence suggests that though resilience against increasing extreme weather events is to be worked for and hope for, it is not to be expected.

A large number of large adverse climate change impacts are not captured  by the models that the assessments are based on. There is no assessment of the real world crop losses from a number of ​combined adverse impacts as is bound to happen.

Even so the USDA ​assessment puts America in an emergency situation for food production. This is because we cannot significantly influence the temperature increase by 2040.Therefore even by the USADA assessment the US is locked into future crop losses. As it is the climate system inertia locks us into a warming of 3C by 2100 which may happen as early as 2050.

Presumably in large part because the American public ​​ is not aware the country is locked into future food production declines there is no big public push for reductions in greenhouse gas emissions and the 2013 Obama Climate Action Plan will result in continuing record US fossil fuel production.

Key messages​​

Increases of atmospheric carbon dioxide (CO2 ), rising temperatures, and altered precipitation patterns
will affect agricultural productivity. Increases in temperature coupled with more variable precipitation will reduce productivity of crops, and these effects will outweigh the benefits of increasing carbon dioxide. ​Effects will vary among annual and perennial crops, and regions of the United States; however, ​all production systems will be affected to some degree by climate change. Agricultural systems ​depend upon reliable water sources, and the pattern and potential magnitude of precipitation
​changes is not well understood, thus adding considerable uncertainty to assessment efforts. ​

​​Livestock production systems are vulnerable to temperature stresses. An animal’s ability to adjust its metabolic rate to cope with temperature extremes can lead to reduced productivity and in extreme cases death. Prolonged exposure to extreme temperatures will also further increase production costs and productivity losses associated with all animal products,
e.g., meat, eggs, and milk.

​​Projections for crops and livestock production systems reveal that climate change effects over the next 25 years will be mixed. The continued degree of change in the climate by midcentury and beyond is expected to have overall detrimental effects on most crops and livestock.

Climate change will exacerbate current biotic stresses on agricultural plants and animals. Changing pressures associated with weeds, diseases, and insect pests, together with potential changes in timing and coincidence of pollinator lifecycles, will
affect growth and yields. The potential magnitude of these effects is not yet well understood.

(These are not captured by the climate crop models and not accounted for in the assessments.​)

​​Agriculture is dependent on a wide range of ecosystem processes that support productivity including maintenance of soil quality and regulation of water quality and quantity. Multiple stressors, including climate change, increasingly compromise the ability of ecosystems to provide these services. Key near-term climate change effects on agricultural
soil and water resources include the potential for increased soil erosion through extreme precipitation events, as well as regional and seasonal changes in the availability of water resources for both rain-fed and irrigated agriculture.

​​(These are not captured by the climate crop models and not accounted for in the assessments.​)

​​The predicted higher incidence of extreme weather events will have an increasing influence on agricultural productivity. Extremes matter because agricultural productivity is driven largely by environmental conditions during critical threshold periods of crop and livestock development.

​​(These are not well captured by the climate crop models and not accounted for in the assessments.​)

The extraordinary thing about this and other climate change assessments is that no consideration is given for the possibility, let alone the likelihood,  that ​we are not able to adapt with any success to global climate change induced crop production declines. It is as if it is assumed that we are not going to cut emissions to prevent food production losses. This assessment documents unavoidable future food production but concluded that response will be adaptation, education and more research. Large greenhouse emissions cuts have been recommended for decades, but not in the conclusion of this US assessment.


The direct effects of changing temperature and precipitation patterns are widely acknowledged and investigated.

Producers and researchers have traditionally faced challenges of temperature and moisture changes with success. However the short-term high variability of weather events currently being experienced are outside of the realm of experience for the agricultural community. Given a continued trend of this variability, a shift of management focus from mostly average conditions to that of focus on managing average plus extreme conditions may well be advised.

The addition of “event duration” or “maximum tolerable change per day,” especially for sensitive growth stages, are potential additions to threshold tables defining the temperature and moisture limits for specific crops. Dealing with the weather manifestations of climate change will be integral to decision making for future producers, more so than for that of past generations.

The complex nature of the agroecosystem means that effects of climate change on system components will vary broadly across geographies and temporal scales. Assessing the full effect of climate change on U.S. agricultural products will require integrated studies that incorporate the nuances of ecosystem function such as soil make-up, changes in timing of runoff, and effects of changing temperature patterns and CO2 concentrations, together with factors related to production economics, management strategy approaches and implementation, and adaptation practices.

Such studies will also feed creation of models that may more accurately project future changes and assess effects of land-use or water-resource changes that may affect crops, and assist with developing strategies that can provide insights on
increasing efficient use of available resources.

Extreme Events

Climate change projections into the future suggest an increased variability of temperature and precipitation. Extreme climate conditions, such as dry spells, sustained drought, and heat waves can have large effects on crops and livestock.

Although climate models are limited in their ability to accurately project the occurrence and timing of individual extreme events, emerging patterns project increased incidence of areas experiencing droughts and periods of more intense precipitation.

The occurrence of very hot nights and the duration of very low (agriculturally insignificant) rainfall events are projected to increase by the end of the 21st century. The timing of extreme events relative to capacity of U.S. agriculture to climate change.

Attention to these research needs will enhance the ability of the U.S. agriculture sector to anticipate and respond to the challenges presented by changing climate conditions.
Climate Change and Food Security

Climate Change &
​in the United States​
US croplands (above) with detailed legend
2015, USDA Climate Change, Global Food Security, and the U.S. Food System
Wealthy populations and temperate regions that are not close to limiting thresholds for food availability, access, utilization, or stability are less at risk. Some high-latitude regions may actually experience near term productivity increases due to high adaptive capacity, CO2  fertilization, higher temperatures, and precipitation increases. However, damaging outcomes become increasingly likely in all cases from 2050–2100 under higher emissions scenarios

The potential of climate change to affect global 
food security is important for food producers and consumers in the United States. The United States is part of a highly integrated global food system: climate-driven changes in the United States influence other nations, and changes elsewhere influence the United States. ​

​The United States is the largest global exporter of 
corn, is among the top wheat and rice suppliers, and is responsible for one-quarter of the world’s meat exports. These exports represent “virtual water” that can compensate for the effects of climate change on water resources in arid and semiarid regions around the world. ​

Increases in precipitation totals and intensity do not necessarily mean that additional water is available for agriculture. More intense rain leads to faster runoff, and higher temperatures increase evapotranspiration losses to the atmosphere, both of which result in less moisture retention in soils.
The entire United States is projected to warm substantially in the future. Even under a scenario of limited emissions increases and GHG concentrations (e.g., RCP 2.6), average temperatures are likely to increase by 1–2 °C over the next 40 years, which is substantially faster than the rate observed over the last 100 years​

​The changes in precipitation and temperature outlined above are extremely likely to have direct effects on U.S. agricultural production. Crops and livestock are sensitive to direct effects of climate changes, such as changing temperatures and
precipitation. Exceeding optimum temperatures for crops steadily reduces productivity up to a threshold, after which productivity decreases sharply, and increases animal stress, especially when coupled with high humidity. Precipitation decreases can make it difficult to store and deliver adequate water to crops at the right time, while increased overall
precipitation, and particularly increased intense precipitation, requires improved drainage to avoid
crop and soil damage.
Agriculture is also sensitive to indirect effects, such as increases in diseases and pests, and degradation of the natural-resource base, such as high quality soil and water, upon which agriculture depends. Climate change is projected to increase the growth and range of many weeds, insect pests, and pathogens​ harmful to agriculture, although the ranges of some invasive weeds could decrease.

​​Projected increases of intense precipitation coupled with increased drying of soils from higher temperatures increases
the risk of accelerated erosion of soils in many areas, which both degrades soil quality and increases the runoff of agricultural chemicals. Projected changes in precipitation are also likely to increase water-management challenges in agriculture. For
example, the combination of decreased snowfall and snowpack, increased rainfall (from less precipitation falling in frozen form and more in liquid form), earlier snowmelt, and decreased summer flows in streams and rivers could increase the need for water storage in many areas of the western United States. 

​Overall, the U.S. food system is expected to be fairly resilient in the near term due to its capacity to undertake adaptive actions such as increased irrigation, shifting of crop rotations and acreage devoted to specific crops in some regions, and alteration of nutrient inputs and other management practices. As climate change continues and temperature increases of 1–3 °C are coupled with changes in precipitation timing and intensity, yield​ and farm returns are projected to decline.

continued changes expected between 2050 and 2100 under high-emissions scenarios are expected to have overall detrimental effects on most crops and livestock.

​​Finally, it should be recognized that 
there is a significant chance that current projections underestimate potential declines, because most analyses exclude production constraints arising from increased pest pressures, extreme events, and decreased ecosystems services (Walthall et al. 2012).
2017,  Xin-Zhong Lian, Determining climate effects on US total agricultural productivity,