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Impacts of climate change on biological systems. David B. Lobell dlobell@stanford.edu. Outline: Some Basic Principles Observed Impacts Projected impacts Several slides taken from NAS report on stabilization targets http://dels.nas.edu/Materials/Presentations/Stabilization-Targets.
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Impacts of climate change on biological systems David B. Lobell dlobell@stanford.edu Outline: Some Basic Principles Observed Impacts Projected impacts Several slides taken from NAS report on stabilization targets http://dels.nas.edu/Materials/Presentations/Stabilization-Targets
Plants grow better in higher CO2 Photosynthesis: CO2 + H20 sugar + O2
Plants grow better in higher CO2 Photosynthesis: CO2 + H20 sugar + O2 Water use efficiency:
Measuring the CO2 fertilization effect FACE: Free-air CO2 enrichment (Long et al. 2006)
Plants usually grow worse in higher temperatures 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
Animal impacts Food sources changing in quantity, quality, and composition Many animals affected by loss of sea and land ice Migratory animals affected by change in seasons
Observed Impacts (not easy to “observe” impacts)
Option 1: show a big co-incidence of climate and biological changes
Option 1: show a big co-incidence of climate and biological changes ELAINE: Well, I mean, he was in the apartment, and then it's gone and it's in your apartment. RAVA: Maybe you think we're in cahoots. ELAINE: No, no.. but it is quite a coincidence. RAVA: Yes, that's all, a coincidence! ELAINE: A big coincidence. RAVA: Not a big coincidence. A coincidence! ELAINE: No, that's a big coincidence. RAVA: That's what a coincidence is! There are no small coincidences and big coincidences! ELAINE: No, there are degrees of coincidences. RAVA: No, there are only coincidences! ..Ask anyone! http://www.seinfeldscripts.com/TheStatue.htm
Option 2: run a model with and without observed climate changes
Recent and Future CO2 levels A2 A1b 2 x pre-industrial B1
Projections for average global temperatures IPCC, 2007
Average climate model projections of soil moisture change by 2080 IPCC, 2007
Food: Large potential decreases in certain crops and locations
Wildfire in the western US(1-2°C warming) Western US
Ocean Acidification and Corals Photo courtesy of Ove Hoegh-Guldberg Global coral reef distribution and biological production of calcium carbonate skeleton (shell material) taking into account both ocean acidification and thermal bleaching 20
Can’t separate “biological” and “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 • Trade • Management or genetic changes
Human responses to climate change • Trade Cool nations “win” Warm nations “lose” One example of estimated impacts for 2x CO2 (from Cline 2007)
Summary • Higher CO2 generally helps (except for C4 plants in moist areas) • Warming generally hurts (except where its very cold) • Precipitation changes are small at global scale, but could be important in some places • There are various forms of evidence for observing impacts, none of them perfect • Projections tend to focus on things we understand pretty well, but there are lots of things that could change that we can’t really quantify (e.g., what are the impacts of climate change on national security?) • For human systems (e.g., agriculture) understanding adaptation is important
Human responses to climate change 2) Management changes Red = no management changes Green = “adaptation” IPCC, 2007
Direct effects of climate change -So warming can have some positive and some negative effects. -The net balance differs depending on crop and location -Overall, crops in most regions prefer cooler temperatures Average Global Yields vs. temperatures, 1961-2002 Yield Change (%) Temperature Change (ºC)