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Climate Change

Science Supporting Policy in California and Beyond

Photo: Louise Jackson of UC Davis

Louise Jackson studies intensive to low input agriculture to discover how these landscapes can be managed to reduce greenhouse gas emissions.


How will climate change affect land use and biodiversity in California's agricultural landscapes?

Louise Jackson; land, air, water resources; anticipates climate change impacts on agricultural systems. She coauthored "Climate Change, Challenges and Solutions for California Agricultural Landscapes" to the California Energy Commission and California Environmental Protection Agency. Jackson’s research compares ecosystem services across farmscapes and along gradients from intensive, irrigated agriculture to low input, grazed, upland systems in California. She has also compared organic and conventionally grown tomato fields, and discovered differences in nitrous oxide emissions and nitrogen retention that increase the mitigation potential for greenhouse gas reduction in organic systems. Comparisons have also been made between processes that increase carbon storage in conventional, reduced tillage, and no-tillage agricultural systems.

Will climate change increase the need for irrigation in California?

Jan Hopmans, chair; land, air, water resources; has a hydrologic modeling study underway to evaluate the long-term impacts of climate change on crop water requirements, soil salinity and groundwater quality in the Central Valley. For that purpose, projected temperature and precipitation information from a selected group of climate change models was used to estimate crop transpiration (ET) for the next 100 years. Using historical water availability data, a sensitivity analysis was conducted that showed that crop ET values are not likely to increase because of the increasing atmospheric carbon dioxide concentrations. However, much uncertainty remains because of the large unknown heat tolerance for the wide range of crops grown in the Central Valley. Model sensitivity results were also used to evaluate irrigated agriculture specifically in the San Joaquin Valley.

Can California offset greenhouse gas emissions through increasing carbon dioxide absorption by perennial crops?

David R. Smart, viticulture & enology, is examining nitrogen use and carbon sequestration by California’s perennial crops. Agricultural systems, in particular those producing woody plants like orchards and vineyards, can both consume and produce the three major greenhouse gases of carbon dioxide, nitrous oxide and methane. Absorption of carbon dioxide that is not immediately released to the atmosphere can be stored in soils, roots and woody tissues, and is referred to as carbon sequestration. Large information gaps exist concerning how much carbon might be sequestered by perennial crops in California, and how management practices for nitrogen fertilizers applied to orchards and vineyards can be utilized in a manner that would reduce nitrous oxide emissions. The students and postdoctoral scholars in Dr. Smart’s laboratory work on several facets of this question, including turnover and decomposition of roots in vineyards and orchards, changes in emissions of carbon dioxide and nitrous oxide following fertilization and irrigation, and quantitative comparisons of carbon and nitrogen emissions in perennial crops with natural ecosystems. One overall objective is to determine how our agricultural systems can be managed in ways that partner with State and Federal agencies in order to improve California air quality.

How will agriculture be a source and a sink for greenhouse gases under a changing climate?

Johan Six, plant sciences, is collaborating with scientists at the Natural Resource Ecology Laboratory, Colorado State University, in an investigation of how global warming might increase carbon dioxide emissions in grassland and agricultural ecosystems. They have found that agricultural lands are going to be further depleted in soil carbon with global warming. His lab group is also collaborating with Richard Howitt, agricultural economist, to determine whether agricultural practices such as cover cropping, reducing fertilizers, manuring and conservation tillage are economically feasible practices to increase soil carbon and reduce the emissions of other greenhouse gas. They are doing this by integrating ecosystem models with economic models. The state of California is interested in these outcomes to better understand how carbon trading might help energy suppliers comply with future reductions in greenhouse gas emissions.

How is projected climate change in California and internationally likely to affect economic prospects for California agriculture?

Dan Sumner, director, Agricultural Issues Center, expects many adjustments in California agriculture over the next several decades -- climate change being only one. He observes that market effects caused by changes in supply and demand shifts outside of California may be more important than impact on production in California. California producers will seek comparative advantages by gradually adjusting what they produce, with some crops moving north and new crops introduced. Yields may decline or become more variable, but changes in price caused by climate change outside of California will affect what is produced and the income earned.

What is the effect of reduced tillage on greenhouse gas release and sequestration from agricultural fields?

Kyaw Tha Paw U; land, air, water resources; collaborates with UC Davis researchers on studies funded by the Kearny Foundation to predict the effects of tillage on carbon sequestration in agricultural soils. Paw U has expertise in biometeorology, a branch of atmospheric science that studies the physical processes that govern exchanges between biological surfaces and the lower atmosphere. These exchanges include motion, heat and water vapor, and monitoring various gases from soils and plants in agricultural fields. He has monitored gases from fields that grow wheat, corn, sunflower and chick peas. The purpose of these studies is to determine if irrigated agricultural systems are a useful means of mitigating or “offsetting” greenhouse gas emissions.

How do elevated carbon dioxide and ozone levels affect carbon and nutrient dynamics in agroecosystems?

Valerie Eviner, plant sciences, collaborates with scientists at the University of Illinois and USDA-ARS, Minnesota, to determine how elevated carbon dioxide and ozone impact plant and soil carbons. They have found that elevated carbon dioxide and ozone can alter crop traits, which then alter nutrient and carbon dynamics. These changes in how carbon moves between the atmosphere and crops have the potential to alter long-term productivity and feedback to climate change.

What is sustainable agriculture and how is sustainable agriculture research and education adapting to climate change?

Thomas Tomich is founding director of the new Agricultural Sustainability Institute, inaugural holder of the Kellogg Chair in Sustainable Food Systems, and professor of community development, environmental science and policy. He is also director of the UC Agriculture and Natural Resources statewide Sustainable Agriculture Research and Education Program (SAREP). The institute provides leadership for research, teaching and outreach and extension efforts in agricultural sustainability. The fundamental definition of sustainability is described by Tomich as: Development that meets the needs of the present without compromising the needs of future generations. Details of sustainability differ from place to place. In California, the economic, environmental and social dimensions of agriculture, food, nutrition and health are interconnected. Leadership in California sustainability focuses on sophisticated science and methods in agriculture, not production of low-cost agricultural products. Tomich develops proof of concept in methods for improving land, air, and water quality. UC Davis College of Agricultural and Environmental Sciences has at least 150 faculty focusing on some aspect of sustainability and about the same number of SAREP graduate students. Adaptation to climate change involves scales from the molecular to global and includes the role of agriculture in the watershed, state policy such as AB32, public investment, and demonstration of new technologies such as methane digesters for dairy operations.

How is undergraduate teaching in agricultural economics incorporating climate change into the curriculum?

Lovell “Tu” Jarvis, Divisional Associate Dean for Human Sciences, College of Agricultural and Environmental Sciences, teaches an undergraduate course in agricultural and resource economics that examines global population, agriculture, and natural resource economics, over half of which is dedicated to causes of and policy responses to global climate change. As a professor in agricultural and resource economics, Jarvis conducts research on agricultural development and agricultural policy in less-developed countries, particularly in Latin America.

Randy Dahlgren, director, Kearney Foundation of Soil Science, TMDL Research and Technical Support Program, examines hydrological, biological, and geochemical interactions in soil and water. Soils are a critical component of ecosystems providing storage pools for nutrients, water, air, and support for plants. The interactions of water, soil and plant life regulate groundwater and surface water quality. Dahlgren’s goal is to gain an understanding of ecosystem-scale biogeochemical processes for the purpose of predicting how to manage sustainability and environmental quality. Many important nutrient cycles, including water, carbon and nitrogen, occur in soil and the sustainability of a particular ecosystem is intimately linked to the quality of the soil.