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A National Assessment on Climate Change and Agriculture

Carl Bolster  

Carl Bolster is a research hydrologist at the ARS Food Animal Environmental Systems Research Unit in Bowling Green, KY, and served as Chapter Lead for the Agriculture, Food Systems, and Rural Communities chapter of the Fifth National Climate Assessment.

Welcome Dr. Bolster to Under the Microscope.

UM: What is the National Climate Assessment?

CB: The National Climate Assessment (NCA) is a report prepared by the U.S. Global Change Research Program that synthesizes the findings of thousands of scientific studies focusing on climate change trends and impacts across the U.S. The NCA evaluates vulnerabilities and risks associated with climate change in multiple sectors including agriculture, energy, human health, land and water resources, transportation, social systems, and the natural environment.

UM: Who is the NCA being produced for?

CB: The NCA is intended to inform policymakers, businesses, and the public about the latest science on climate change and the risks it poses to different sectors and regions of the U.S. The NCA does not make any policy recommendations but rather synthesizes highly technical information to inform decision-makers in local, state, national, and Tribal governments; farmers; teachers; researchers; community organizers; the media; and concerned citizens, among others about the risks posed by climate change. 

UM: There is so much on the web about climate change; it can be challenging to know what is backed by science and what is misinformation. What is the solid science behind this Assessment?

CB: The Fifth NCA was written by over 500 authors and 260 technical contributors who are experts on climate change. The authors synthesize the findings of thousands of scientific studies and carefully assess the quality of the evidence and the level of agreement on that evidence within the scientific community. The report went through eight reviews, including multiple reviews from 14 Federal Agencies and was reviewed by an ad hoc committee of the National Academies of Science, Engineering, and Medicine. Early drafts of the report were also made available to the public for review. The sources used by the authors in writing the NCA must meet the standards of the Information Quality Act and the Foundations for Evidence-Based Policymaking Act of 2018.

UM: In the section pertaining to agriculture, the NCA discusses the serious challenges climate change poses to U.S. agricultural production, food systems, and rural communities. What are these challenges?

CB: Agriculture has always faced unpredictable weather, but a changing climate poses additional challenges by changing historical patterns in precipitation and temperature, which require changes in agricultural practices such as crop selection and management approaches. Climate change is projected to disrupt food systems in ways that reduce the availability and affordability of nutritious food, with uneven economic impacts across society. Rural communities who steward much of the Nation’s land and natural resources are at risk as climate change compounds existing stressors such as poverty, unemployment, and depopulation in these communities.

UM: Okay, let’s tackle these one by one. "Important Disruptions to Agriculture." How do you see climate change disrupting agriculture today and in the near future?

CB: Shifts in growing seasons; more frequent and/or extreme weather events such as droughts, heat waves, and heavy rainfall; increased soil degradation and erosion; increased flooding; increased pest and disease pressure; and increased heat stress on farm workers and livestock. These can all adversely affect agricultural production by damaging crops, delaying planting and harvesting, reducing crop yields, and increasing heat stress on livestock and farm workers.

UM: Your second key message is, "All Dimensions of Food Security will be Adversely Affected." This includes the agricultural workforce, please explain.

CB: Climate change can adversely affect food security by causing disruptions throughout the food supply chain, including production, storage, processing, distribution, retail, and consumption. These disruptions can make food more expensive, less accessible, less usable, and less stable. An example of this directly affecting agricultural workers is when an event such as an extreme drought or a major flood destroys a crop or significantly reduces its yield, resulting in lower demand for farm labor to harvest the crop. This in turn can lower farm workers’ income and their ability to purchase food.

UM: In this section, you also talk about the need to reduce food loss and waste and reduce greenhouse gas emissions (GHG). How can these goals be achieved while combatting the effects of climate change?

CB: It is estimated that 30% to 40% of food eventually spoils or is wasted, largely at the consumption stage. When we consider that the food supply chain consists of production, distribution, retail, and finally consumption, the further along in the supply chain that food waste occurs, the more energy and GHG emissions have been released to produce food. By reducing food loss and waste, particularly at the consumption stage, GHG emissions would be significantly reduced while at the same time increasing food security.

UM: Your third key message addresses "Rural Community Impacts, Challenges, and Opportunities."  You bring up an interesting point in this message, noting that "the resiliency of rural communities to climate change is hindered when climate risks are compounded by historical environmental justice inequities." Can you explain?

CB: One example is that of historically marginalized communities located in flood-prone areas. These communities have lacked investments in flood protection infrastructure and adequate disaster preparedness plans. As climate change intensifies the frequency and severity of extreme weather events like hurricanes, storms, and heavy rainfall, these flood-prone communities are at greater risk than areas which have adequate infrastructure and appropriate disaster plans. As a result, these communities are likely to experience greater loss of life and property.

UM: What are your major recommendations in your chapter of the NCA, and how can they be applied today?

CB: While we do not make recommendations in our chapter of the Assessment, we do emphasize that adopting agroecological approaches can lead to increased productivity, resilience to climate change, and reductions in GHG emissions. These approaches include a focus on soil health, adaptive conservation management, diversification of landscapes, and precision technologies that target the right amount, source, placement, and timing of nitrogen fertilizers.

UM: Is there an urgency to make more progress in agriculture to combat climate change?

CB: Yes, to reduce the risks posed by a changing climate will require rapidly reducing GHG emissions, not only from agriculture but from all sectors. It is urgent that we achieve net zero emissions by mid-century in order to limit future warming and the associated risks that come with a warmer planet. 

UM: Along those lines, are there areas where we are making progress and areas where much more progress needs to be made?

CB: Over the past 30 years, increased efficiencies in agricultural have resulted in lower GHG emissions per capita and unit of agricultural productivity; however, total emissions from U.S. agriculture still make up roughly 10% of annual emissions in the U.S.; making it the fourth largest contributor to GHG emissions by sector trailing only transportation, electricity generation, and industry. This highlights the need for continued progress in GHG emission mitigation in the agricultural sector.

UM: What gives you optimism that agriculture in this country can meet the challenges faced by climate change?

CB: Farmers have experienced firsthand the effects of changing weather patterns on their livelihoods. As a result, there is growing recognition for the need to mitigate GHG emissions, adapt to climate change, and increase resiliency to climate change. The increased awareness and desire to implement farming methods that reduce nitrous oxide emissions through improved nitrogen management, providing methane-reducing feed supplements to ruminant livestock, capturing methane from manure lagoons, and adopting conservation-based practices that increase carbon sequestration gives me optimism that U.S. agriculture can meet these challenges. Meeting these challenges, however, will require cooperation between farmers, policy makers, scientists, and engineers.

Chapter 11 of the NCA report, pertaining to agriculture, can be accessed here Agriculture, Food Systems, and Rural Communities ( The entire report can be accessed here Fifth National Climate Assessment (