Image courtesy of NASA/GSFC

Global Climate Change: What About Agriculture? Eugene S. Takle Director, Climate Science Initiative Professor of Atmospheric Science Department of Geological and Atmospheric Sciences Professor of Agricultural Meteorology Department of Agronomy Iowa State University Ames, Iowa 50011 gstakle@iastate.edu iPlant Collaborative Biosphere II 27 September 2008

Source: IPCC, 2001: Climate Change 2001: The Scientific Basis

Source: IPCC, 2001: Climate Change 2001: The Scientific Basis

http://www.ncdc.noaa.gov/img/climate/research/2006/ann/glob_jan-dec-error-bar_pg.gif

Source: Jerry Meehl, National Center for Atmospheric Research From Jerry Meehl This slide shows the time evolution of globally averaged surface air temperature from multiple ensemble simulations of 20th century climate from the NCAR Parallel Climate Model (PCM) compared to observations. The simulations start in the late 19th century, and continue to the year 2000. The temperature scale at left is in degrees Centigrade, and temperature anomalies are calculated relative to a reference period averaged from 1890 to 1919. The black line shows the observed data, or the actual, recorded globally averaged surface air temperatures from the past century. The blue and red lines are the average of four simulations each from the computer model. The pink and light blue shaded areas depict the range of the four simulations for each experiment, giving an idea of the uncertainty of a given realization of 20th century climate from the climate model. The blue line shows the average from the four member ensemble of the simulated time evolution of globally average surface air temperature when only "natural" influences (solar variability and volcanic eruptions) are included in the model. Therefore, the blue line represents what the model says global average temperatures would have been if there had been no human influences. The red line shows the average of the four member ensemble experiment when natural forcings AND anthropogenic influences (greenhouse gases including carbon dioxide, sulfate aerosols from air pollution, and ozone changes) are included in the model. Note that this model can reproduce the actual, observed data very well only if the combined effects of natural and anthropogenic factors are included. The conclusion that can be drawn is that naturally occuring influences on climate contributed to most of the warming that occurred before WWII, but that the large observed temperature increases since the 1970s can only be simulated in the model if anthropogenic factors are included. This confirms the conclusion of the IPCC Third Assessment Report that most of the warming we have observed in the latter part of the 20th century has been due to human influences. Source: Jerry Meehl, National Center for Atmospheric Research

IPCC Fourth Assessment Report Summary for Policy Makers

Energy intensive Energy conserving Mitigation Possible Adaptation Reduced Consumption Energy conserving Possible Mitigation Necessary Adaptation IPCC Fourth Assessment Report Summary for Policy Makers

Projected changes in precipitation between 1980-1999 and 2080-2099 for an energy-conserving scenario of greenhouse gas emissions IPCC 2007

Precipitation minus Evaporation for Western US (25N-40N, 95W-125 W) R. Seager, et al.,2007. Model Projections of an Imminent Transition to a More Arid Climate in Southwestern North America. Science, Vol. 316. no. 5828, pp. 1181 - 1184

Projected Changes* for the Climate of the Midwest Temperature Longer frost-free period (high) Higher average winter temperatures (high) Fewer extreme cold temperatures in winter (high) Fewer extreme high temperatures in summer in short term but more in long term (medium) Higher nighttime temperatures both summer and winter (high) More freeze-thaw cycles (high) Increased temperature variability (high) *Estimated from IPCC reports Follows trend of last 25 years and projected by models No current trend but model suggestion or current trend but model inconclusive *Estimated from IPCC reports

Projected Changes* for the Climate of the Midwest Precipitation More (~10%) precipitation annually (medium) Change in “seasonality”: Most of the increase will come in the first half of the year (wetter springs, drier summers) (high) More water-logging of soils (medium) More variability of summer precipitation (high) More intense rain events and hence more runoff (high) Higher episodic streamflow (medium) Longer periods without rain (medium) Higher absolute humidity (high) Stronger storm systems (medium) More winter soil moisture recharge (medium) Snowfall increases (late winter) in short term but decreases in the long run (medium) *Estimated from IPCC reports Follows trend of last 25 years and projected by models No current trend but model suggestion or current trend but model inconclusive

Projected Changes* for the Climate of the Midwest Other Reduced wind speeds (high) Reduced solar radiation (medium) Increased tropospheric ozone (high) Accelerated loss of soil carbon (high) Phenological stages are shortened high) Weeds grow more rapidly under elevated atmospheric CO2 (high) Weeds migrate northward and are less sensitive to herbicides (high) Plants have increased water used efficiency (high) *Estimated from IPCC and CCSP reports Follows trend of last 25 years and projected by models No current trend but model suggestion or current trend but model inconclusive

Suitability Index for Rainfed Agriculture IPCC 2007

Suitability Index for Rainfed Agriculture IPCC 2007

Projected changes in precipitation between 1980-1999 and 2080-2099 for an energy-conserving scenario of greenhouse gas emissions IPCC 2007

US Corn Yields (Bushels/Acre)

Grain and oilseed consumption has exceeded production 7 of last 8 years Tostle, Ronald, 2008: Global Agricultural Supply and Demand: Factors Contributing to the Recent Increase in Food Commodity Prices WRS-0801 May 2008. USDA/ERS

Lingering Questions Relating to Food Production and Climate Change What regions now suitable for rainfed agriculture will become marginally suitable or unsuitable due to climate change? What regions now unsuitable for rainfed agriculture might become suitable?

Lingering Questions Relating to Food Production and Climate Change By how much will technological advances reduce the impact of climate change on agriculture? Continued advances in drought tolerance for corn Drought or excess-water tolerance for all crops Availability (e.g., water), sustainability and political acceptance of expanded irrigation for agriculture What dietary changes will occur that will impact demand? Relative amount of meat in diets? New crops? More locally produced food?

Summary Global temperature change of the last 30 years cannot be explained on the basis of natural radiative forcing alone. Only when anthropogenic effects are considered can we explain recent temperature trends Mitigation efforts, although urgently needed, will have little effect on global warming until the latter half of the 21st century Adaptation strategies should be developed for the next 50 years Impact of climate change on global food production is yet to be evaluated with the most recent generation of global climate models