USDA outlines climate change impacts on agriculture, forestry

By Erin Voegele | February 12, 2013

In early February, the USDA released two reports that outline the impact of climate change on U.S. agriculture and forestry. The papers also address  possible adaptation strategies. The reports, titled “Climate Change and Agriculture: Effects and Adaptation,” and “Effects of Climate Variability and Change on Forest Ecosystems: A Comprehensive Science Synthesis for the U.S. Forest Sector,” are inputs to the National Climate Assessment.

“These reports present the challenges that U.S. agriculture and forests will face in this century
from global climate change,” said William Hohenstein, Director of the Climate Change Program
Office in USDA’s Office of the Chief Economist. “They give us a framework for understanding
the implications of climate change, in order to meet our future demands for food, feed, fiber, and

According to the agriculture report, climate change poses unprecedented challenges to U.S. agriculture due to the sensitivity of productivity and costs to changing climate conditions. However, the USDA said that adaptive actions should help manage climate change impacts while capitalizing on emerging opportunities. In the short term, the USDA expects U.S. agriculture to be fairly resilient to climate change due to the flexibility to engage in adaptive behaviors, such as increased irrigation or regional shifts in crop acreage. In the longer term, the USDA said it expects yields of major crops and farm returns to decline. These declines are associated with temperature increases that are expected to exceed 1 to 3 degrees Celsius by mid-century, along with the intensification of precipitation extremes.   

The report specifies that rising temperatures and altered precipitation associated with climate change will reduce crop productivity. These reductions will outweigh the benefits of increased levels of atmospheric carbon dioxide (CO2). While effects will vary among annual and perennial crops, the USDA notes that all crop production systems will be affected to some degree. In the report, the USDA also stresses that the pattern and potential magnitude of precipitation changes associated with climate change are not well understood, and add considerable uncertainty to assessment efforts.

The USDA said that climate change will exacerbate current biotic stresses on agricultural plants. “Changing pressures associated with weeds, diseases, insect pets, together with potential changes in timing and coincidence of pollinator lifecycles, will affect growth and yields,” said the authors in the report, noting that the potential magnitude of these effects is not well understood at this time.

In the short term, the USDA said that the potential for increased soil erosion through extreme precipitation events will affect the agricultural industry. Regional and seasonal changes in water availability, for both rain-fed and irrigated agriculture, will also have an impact.

According to the report, vulnerability of the agricultural sector will be affected by human response. “The vulnerability of agriculture to climatic change is strongly dependent on the responses taken by humans to moderate the effects of climate change,” said the USDA in the report. “Adaptive actions within agricultural sectors are driven by perceptions of risk, direct productivity effects of climate change, and by complex changes in domestic and international markets, policies, and other institutions as they respond to those effects within the United States and worldwide.”

Some adaptation measures anticipated by the USDA include adjustments to production system inputs, tillage, crop species, crop rotations and harvest strategies. According to the report, the development of new crop varieties that are more resistant to drought, disease and heat will not only increase resilience of agronomic systems, but will also enable exploitation of opportunities that may arise.

The forestry report also outlines expected negative impacts associated with climate change. In the long-term, the USDA points out that increasing temperatures, changes in precipitation, higher concentrations of CO2 and higher nitrogen deposition could change the structure and function of ecosystems. However, short-term impacts associated with climate change are expected to result from disturbance regimes, such as wildfires, insect infestations, erosion and flooding, and drought-induced tree mortality.

According to the USDA, increasing temperatures will reduce the growth of some tree species, particularly those in dry forests, while increasing the growth of others, including high-elevation forests. Older forests may be subject to increased mortality due to low soil moisture. Regeneration may also decrease for species affected by low moisture and competition with other species. However, most tree species are tolerant to a broad range of environmental conditions. For these species, tree growth and regeneration could be more significantly impacted by extreme weather events and climatic conditions. Overall, the USDA notes that models currently predict forestry habitats will move upward in elevation and northward in latitude.

Regarding disturbance regimes, the USDA notes that wildfire is expected to increase, causing the area of land burned to more than double by mid-century. In addition, insect infestations will expand, affecting more land area per year than wildfire. Invasive species will also become more widespread, while increased flooding, erosion and sediment into streams will also occur. In addition, increased drought will exacerbate many of these stresses.