Transcript Lobell_Slides

Impacts of climate change on
food production
David B. Lobell
[email protected]
Recent and Future CO2 levels
A2
A1b
2 x pre-industrial
B1
Projections for average global temperatures
IPCC, 2007
Measuring the CO2 fertilization effect
FACE: Free-air CO2 enrichment
(Long et al. 2006)
Direct effects of climate change
The main effects of warming:
-faster rates of development (see below)
-faster rates of photosynthesis and respiration
-higher rates of evapotranspiration (important in dry regions)
-fewer frosts (important in cold regions)
“birth”
“adolescensce”
“adulthood”
“death”
In a cooler year, this process can take ~10 days longer than in warmer
year, which means 10 or more days to photosynthesize
Direct effects of climate change
-So warming can have some positive and some negative effects.
-The net balance differs depending on crop and location
Yield Change (%)
-Overall, crops in most regions prefer cooler temperatures
Average Global Yields vs. temperatures, 1961-2002
Temperature Change (ºC)
Crop Yield Changes for CO2 and climate change
Red = no management changes
Green = “adaptation”
3 questions:
1. What are impacts without
adaptation?
2. How helpful are adaptations?
3. What do yield changes imply for
hunger?
IPCC, 2007
Yield
Temperature
Summary so far
1) Higher CO2 will help crop yields, more so for C3 crops than C4 crops
Summary so far
1) Higher CO2 will help crop yields, more so for C3 crops than C4 crops
2) Warming will reduce yields in most locations
3) Precipitation changes will be important in some areas.
Human responses to climate change
Farmers and scientists are not dumb
In response to these pressures, people are likely to adapt.
Two main types of adaptations
1) Trade
2) Management changes
Human responses to climate change
1) Trade
Cool nations “win”
Warm nations “lose”
One example of estimated impacts for 2x CO2 (from Cline 2007)
Human responses to climate change
2) Management changes
Red = no management changes
Green = “adaptation”
IPCC, 2007
Summary so far
1) Higher CO2 will help crop yields, more so for C3 crops than C4 crops
2) Warming will reduce yields in most locations
3) Precipitation changes will be important in some areas, but projections
of future precipitation are very uncertain.
4) Adaptation will help to reduce impacts on global food production,
assuming that poorer countries can afford to import food, that the
right investments are made in new technologies, and that farmers
implement adaptations quickly enough to avoid big losses. (Three big
assumptions)
5) In tropical countries, impacts could be quite large (up to 30-50%
losses) even in 20 years
6) For the globe, impacts are most likely small until ~2050 or 2xCO2. But
if CO2 levels go much higher than 550 ppm, then effects could be
quite large.
Future CO2 for several emission scenarios
A2
A1b
2 x pre-industrial
B1
What will this mean for the crops we depend on?
Photosynthesis: CO2 + H20  sugar + O2
Most photosynthesis is called C3, but some plants have developed a mechanism to
avoid photorespiration by concentrating CO2 in the leaf interior. This makes them more
productive in very hot and sunny conditions, and less sensitive to changes in CO2
C3 crops: wheat, rice, soybean, barley, and most others
C4 crops: maize (corn), sorghum, millet, sugarcane.
Average climate model projections of soil moisture change by 2080
IPCC, 2007