In Which States Will Agriculture Lose Most from Climate Change?

Photo by Peter Gonzalez on Unsplash
Irrigation

This article was written by UC Davis ARE PhD student Goeun Lee. It is the second in a series of excellent articles written by students in my ARE 231 class this fall.

There are always winners and losers.  According to a recent study from USDA ERS, climate change has an uneven effect on agricultural productivity across the U.S. Who is winning? Is California doing better than other states?

The map below shows different predicted rates of decline in agricultural total factor productivity (TFP) in the U.S. over a 30-year period. TFP is a measure of how much production farmers can get out of their inputs. On the map, a TFP gap index smaller than 1 implies growth in agricultural productivity relative to the reference period (2000-10) and an index bigger than 1 implies a decrease in productivity.

The Lake States, Northern Plains, Delta States, and Southeast region are expected to experience a significant decrease in productivity while the states in the Pacific and Mountain area are relatively free from productivity decline under the climate change scenario of a 2 °C increase and 1-inch decrease in rainfall. There are a few states like California and Oregon where agricultural productivity is predicted to increase even under climate change.

Climate Change and TFP
Source:  Climate Change Likely to Have Uneven Impacts on Agricultural Productivity by Sun Ling Wang, Richard Nehring, and Ryan Williams

 

What explains the difference? The map below provides a clue. Irrigated counties seem to be better prepared for climate change. In fact, ERS’s research suggests that irrigation-system-ready land areas help to mitigate the adverse impacts of climate change on agricultural productivity.

Irrigation
Ratios of irrigated land area to total cropland area (irrigation ratio) at census year. 
Source: Impacts of Climate Change and Extreme Weather on U.S. Agricultural Productivity: Evidence and Projection (2017), by Sun Ling WangEldon BallRichard NehringRyan Williams & Truong Chau

 

The next map provides another clue. Regions growing crops are predicted to have larger decreases in productivity. Indeed, recent research by Ariel Ortiz-Bobea, Erwin Knippenberg, and Robert Chambers suggests that crop production is more sensitive to extreme climates compared to livestock production, especially if farmers focus on a small number of crops such as corn, soybeans and wheat. Specialization in crop production results in increased vulnerability to climate change. For example, farms in Southern Plains that specialize in livestock production are likely to suffer less from climate change than farms that specialize in crop production in the Midwest.

CDL 2019
All crops grown in the U.S. in 2019
Source: Our cropland data layer app

 

The figure below is from the Ortiz-Bobea et al paper. It shows how historical changes in agricultural productivity relate to changes in temperatures over two time periods, 1960-1982 and 1983-2004. Northwest states are getting better in dealing with relatively high-temperature extremes while most of the states including the Midwest and Southeast are getting worse. The historical regional specialization combined with the preparedness of each state (i.e. irrigation, new technologies) decides the winners and losers from climate change.

Climate Effects
Source: Growing climatic sensitivity of U.S. agriculture linked to technological change and regional specialization (2018)

 

Does that mean Midwestern and Southeastern states are doomed? The answer can be “Yes” and “No”. Climate change will obviously put more pressure on productivity growth, but we just saw a silver lining from the map above. The future TFP in this study is projected while fixing prices, input use, technology, and farm practices to the reference level (2000-10). The researchers used the so-called “dumb farmer” assumption (Mendelsohn, Nordhaus, and Shaw (1994); Key and Sneeringer (2014)) where farmers are assumed to ignore any adverse effect from climate change thus not respond to the changing conditions.

The historical irrigation map above shows that farmers have adapted to the climate and they can adapt more. If we realize the expected decrease in TFP and take proper measures in time such as building an irrigation system and increasing R&D to improve technology, we can make a difference in the future.

Can states like California walk away unscathed from this problem? I would say, “not really”. The ERS study takes into account only temperature and precipitation anomalies measured by the degree of deviations from the annual variations during 1941-1970. That’s not the end of the story. It is highly likely that climate extremes (e.g., wildfire and multi-year mega-drought) that California has been experiencing would not be fully counted in the projection. 

For states like California, the projected damages may be underestimated.