Impacts of Climate Change on Agricultural Production Simon Donner Department of Geography University of British Columbia
~40% of the ice-free land Ramankutty et al., 2008
Agriculture and climate Three key interactions: a major driver of climate change (via greenhouse gases and land use change) influenced by climate change may play a role in mitigating climate change
Agriculture climate change In 2005, 16% of global carbon dioxide emissions (deforestation) 57% of global methane emissions (manure, rice) 75% of global nitrous oxide emissions (fertilizers) Together, 1/3 rd of total climate impact, not including fossil fuels used in production!
Climate change agriculture Agriculture = humans harnessing photosynthesis CO 2 + H 2 O + Light CH 2 O + O 2 reaction rate depends on temperature key enzymes require nitrogen, also phosphorus and other nutrients the apparatus can be damaged by ozone
Climate change agriculture Basic biochemistry and biophysics tells us a lot: Increased CO 2 can be beneficial Crops should benefit from a longer growing season Increased temperatures will increase water stress on most crops (except maybe crops like millet that like dry conditions), especially in tropical countries Indirect climate change effects pest outbreaks, response of weeds are still uncertain
In general, expect uneven impacts Change in land suitability for food production by 2070-99 north wins? south loses Ramankutty et al., 2002
Developing world impacts Yield declines for the key crops (esp. S Asia) Calorie availability in 2050 decline (relative to 2000) By 2050, climate change will negate much of gains in child malnutrition US$7.1 7.3 billion needed to offset (40% to Sub- Saharan Africa, followed by S Asia)
What about technology? Crop yields have increased thanks to genetics, chemical fertilizers; data seems to suggest minimal climate impact 180 U.S. average crop yield (bu/acre) 160 140 120 100 80 60 40 20 Corn Wheat Soy 0 1955 1965 1975 1985 1995 2005 2015
Technology vs. climate Climate impact (e.g. moisture stress) seen in the very high year-to-year variability in yield and production U.S. average CORN yield (bu/acre) 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 1860 1880 190019101920 1940 1960 1980 20002010 1800 1600 1400 1200 1000 800 600 400 200 0 Standard deviation (10 yr)
Gray = expected distribution!
Large climate impacts on yield when you control for other factors 3.8% decrease overall Gray = expected distribution! 5.5% decrease overall
Large climate impacts on yield when you control for other factors 29 C
Large climate impacts on yield when you control for other factors 30 C
Large climate impacts on yield when you control for other factors 32 C
Carbon dioxide crop production Early work pointed to CO 2 fertilization of crop growth counter-acting deleterious climate impacts Parry et al. (2004)
Carbon dioxide crop production Early work pointed to CO 2 fertilization of crop growth counter-acting deleterious climate impacts Parry et al. (2004)
Battisti and Naylor (2009) Looking forward: heat stress In the tropics and sub-tropics, growing season temperatures are very likely to exceed the most extreme temperatures today (1980-2006)
Heat stress example 2003 European Heat Wave 30,000-50,000 died Italy: 36% drop in maize yields France: 30% decrease in maize + fodder 25% drop in fruit harvests Battisti and Naylor (2009); NOAA
Heat stress example 2003 European Heat Wave 30,000-50,000 died Italy: 36% drop in maize yields France: 30% decrease in maize + fodder 25% drop in fruit harvests Battisti and Naylor (2009); NOAA
N. American summer drought
N. American summer drought
Mitigation vs. Adaptation? Over 42% of this year's U.S. corn crop went to ethanol. Together with the drought, this led to lowest exports since 1980.
Mitigation vs. Adaptation 30 Corn exports (million metric tons) 25 20 15 10 5 Poor mitigation choices leading to mal-adaptation? 0 USA, by far the largest exporter
Bulk world price, $/bushel August peak: $8.49/bushel Oct. 2 price: $7.58/bushel
Take-home messages Future prediction is hard Small-scale extremes, nutrient feedbacks, etc. not well incorporated in models Human factor: Will farmers adapt to observed changes or predictions? Even if people are rational, they don t have perfect information or ability to use information Uncertainty about technology
Take-home messages What we do know with some certainty: Lower crop yield in developing countries and subtropics; potential increases in the north But threshold responses and extremes may still occur in the north Direct CO 2 benefits likely overstated Pests and pathogens may be important Adaptation may allow us to offset some of the losses, but requires investment Other issues: pests, pathogens, land loss due to sea level rise (significant in developing world)