1. Global Change and Agriculture: The Effects that Plants Have on Climate, and Vice Versa Dennis Baldocchi Professor of Biometeorology Department of Environmental Science, Policy and Management College of Natural Resources State Board of Food and Agriculture July 25, 2007

2. Topics Covered Trends in Temperature –Implications on Winter Chill/Dormancy Trends in Phenology –+/- of Increasing Growing Season Length Trends in Water Use –Pan ET and ‘Solar Dimming’ –Combined effects of Elevated CO 2 and Temperature Trends in Land Use Change –Evaporative Cooling and Albedo change

3. Summary Climate Change is in Motion in California –CA is warming, but interannual variation in rainfall is greater than predicted trends in the near term There is a trend in reduced winter chill and winter dormancy –Leads to a reduction in fruit and nut production –The future trends may not be linear, but could accelerate if winter fog patterns change –Breeding programs are needed to produce cultivars that require less winter chill Spring phenology is advancing –Increase vulnerability of fruit trees to late frost –May increase carbon sequestration, if water is plentiful, and increase water use –may cause a miss-match between flowering and pollinators Water consumption will increase in the future –Potential water ‘savings’ by elevated CO 2 are offset by warmer temperatures –CA is not be experiencing water savings due to ‘solar dimming’. Land use change from Natural to Agricultural Landscapes has altered the surface energy balance –Crops are Darker than grasslands and absorb more energy –But Evaporative cooling reduces air temperature, in comparison

4. Temperature and Agriculture Length of Growing Season Length of Dormant Season Extreme Cold –Fruit, flower, and/or pollination damage Extreme heat –Fruit damage –Leaf damage

5. Camp Pardee, CA Foothill Rangeland Antioch, CA Sac-San Joaquin Delta Temperature Trends, Selected Sites Warming Rate: ~ 1.5 C ++ per 50 Years

6. Estimating Winter Chill

7. Downward Trend in Chill Hours near Brentwood, East Contra Costa 20 year record, CIMIS Data

8. Baldocchi and Wong, Climatic Change, in press Reductions in Winter Chill are being Experienced across the State and they are expected to Continue into the Future

9. Almond Yield (ton acre -1 ) Almond Yield Anomaly D. Lobell et al, 2006 Ag.Forest Met Photo © David Sanger So What?: Almond Yield Decreases with Warmer and Wetter winters

10. Phenology: The Timing of Plant Activities FloweringLeaf-out

11. Schwartz et al. 2006 Global Change Biology Spring is Advancing by about 3 days per Decade across the Northern Hemisphere

12. Estimated Trends in Phenology in CA Rangeland

13. Length of Growing Season, Carbon and Water Exchange Baldocchi et al, 2001 Bull. Am. Meteorol. Soc. Ryu, Baldocchi and Ma, unpublished Annual Grassland, CA Deciduous Forests

14. Water and Agriculture Year to Year Variability Exceeds any Existing or Expected Future Trends Snowpack and the Timing of its Melting will be Affected

15. Evaporation, Water Availability and Climate Change Global Warming Should: –Accelerates the Water Cycle by increasing saturation vapor pressure –Increase Evaporation But Negative Feedbacks include: –Increase Humidity and Cloud Cover –Decrease Solar Radiation, ‘Solar Dimming’ –Widespread Reduction in Pan or Potential Evaporation

16. Liu et al. Journal Geophysical Research, 2004 Pan ET in China Literature is showing a long term trend with a decrease in pan evaporation: Could there be Water Savings for Irrigated Agriculture in CA? Solar Radiation in China

17. Trends in Pan Evaporation in CA: Irrigated Central Valley Semi-Arid Rangeland Hildalgo et al. 2005 J Hydromet: ‘Trends for PET are unclear in CA’

18. Farquhar and Roderick, Pontifical Academy of Science, in press Feedback Loops Break in Water-Limited Regions

19. Lessons from Direct Evaporation Measurements over California Rangeland CA Ecosystem are Water, not Radiation Limited Savanna Uses More Water than Grassland -Savanna Soil holds about 78 mm more Water Annual ET Decreases with Solar Radiation -Rg decreases as Clouds and Rain increase -Range in ET is 100 mm/yr Ryu, Ma and Baldocchi, unpublished

20. Enhances Photosynthesis –Down-Regulation in Ps from Nutrient Limitations Reduces Stomatal Closure –Direct Effect Reduces Transpiration and Increases WUE –InDirect Effect and Positive Feedback Elevated Leaf Temperature, augments Transpiration Greater Growth and Leaf Area –Bigger plants grow faster. + –Bigger plants transpire more –Soil moisture pool depleted faster: - Herbivore Interactions –Insects eat more foliage to compensate for lower N quality of leaves Elevated CO 2, Facts and Myths

21. Projected Water Use in a Walnut Orchard will increase by ~145 mm (6 in) with T+3 C and CO 2 at 500 ppm

22. Agriculture and Land use Change Albedo –Crops are darker than dead grass, so the Absorb more solar energy Evaporation Ratio, E/Rn –Crops do not suffer for soil moisture deficits and are fertilized –They achieve a larger Leaf Area Index and possess lower Surface Resistance than annual grasses or savanna woodlands –Crops experience greater rates of ET and have depressed Surface Temperatures, compared to native vegetation Carbon Uptake –Crops are actively assimilating carbon dioxide during the summer

23. Land Use Change and Climate Change in the Central Valley Kueppers et al, 2007, Geophysical Res. Letters Christy et al, 2004, J Climate Large Scale Irrigation reduces Temperature compared to natural vegetation But Increases Nighttime Temperatures through humidification of the air and increasing downward longwave energy Rate of Climate Warming in CA is dampened due to Land Cse Change -negative feedbacks by evaporative cooling outpace positive effects of lower albedo Difference in Tmax: Natural vs managed land

24. Some Potential Solutions Changes in crops, timing and rotation –Don’t grow crops that are profligate water users in the desert! Irrigation scheduling and soil moisture management Mulches and increased soil organic matter to reduce soil evaporation and runoff Precision agriculture and drip irrigation

25. We are Linked to Past, We have a Responsibility to the Future Palace of Minos at Knossos, ~2000 BC Climate Change is in Motion in California Long term production of valuable fruit crops is vulnerable due to trends in reduced winter chill The future trends may not be linear, but could accelerate if winter fog patterns change Breeding programs are needed to produce cultivars that require less winter chill Water consumption will increase in the future

27. Extra Background Material

28. Temperature Anomaly Trends: Instrument Record

29. Mote et al. 2005 BAMS Trends for Climate between Nov and Mar

30. McKinney et al, 2006 AgForMet

31. Lobell et al 2006 AgForMet

32. Critical Temperatures and Yield

35. Menzel et al 2006 GCB; Menzel and Fabian, Nature, 1999 Regression Coefficient of Phenological Event with Time, days per year Phenology, a Measure of Global Change

36. Feng and Hu, 2004, J Theor Appl Clim Trends, days per Decade

37. Feng and Hu, 2004, J Theor Appl Clim Trends in Growing Season Length and Last Frost Dat United States

38. Christy et al 2006 J Climate

39. Feng and Hu, 2004, J Theor Appl Clim United States Trends in Dry and Wet Spells

42. Global Irrigation Intensity Kueppers et al, 2007; Siebert et al., 2005

43. Christy et al., 2006 J Climate

45. Issues to Consider Regarding Role of C Sequestration to Mitigate Climate Change Vegetation operates less than ½ of the year and is a solar collector with less than 2% efficiency –Solar panels work 365 days per year and have an efficiency of 20%+ Ecological Scaling Laws are associated with Planting Trees –Mass scales with the -4/3 power of tree density Available Land and Water –Best Land is Vegetated and New Land needs to take up More Carbon than current land –You need more than 500 mm of rain per year to grow Trees The ability of Forests to sequester Carbon declines with stand age There are Energetics and Environmental Costs to soil, water, air and land use change –Changes in Albedo and surface energy fluxes –Emission of volatile organic carbon compounds, ozone precursors –Changes in Watershed Runoff and Soil Erosion Societal/Ethical Costs and Issues –Land for Food vs for Carbon and Energy –Energy is needed to produce, transport and transform biomass into energy