how scientists study climate change a rangeland perspective photo: sam cox
TRANSCRIPT
How Scientists Study Climate ChangeA Rangeland Perspective
Photo: Sam Cox
How Scientists Study Climate Change
• Reviewing our present state of knowledge– What we know (accepted by scientists)– Predictions; implications; uncertainty
• How we study the problem (techniques that scientist use, their strengths and limitations) – Observation– Manipulative experimentation – Modeling
WHAT WE KNOW: Atmospheric CO2 concentrations measured accurately for many decades; they are steadily increasing.
Charles David Keeling
1928-2005
2002 Nat’l Medal of Science
Annual cycle due to photosynthesis and respiration of soils.
Long term trend due to emission of fossil fuels
IPCC Working Group I Report, Chapter 2, 2007
WHAT WE KNOW: Ice core sampling & other techniques indicate rising CO2 in Earth’satmosphere is a relatively new phenomenon.
WHAT WE KNOW: A direct effect of rising CO2:
Stimulation of plant growth.
Nutrients, H2O
CO2
Food, GloriousFood!
Any change in light, water, nutrients or carbon dioxide will alter plant growth.
WHAT WE KNOW: Global average surface temperature has increased 0.74 C (1.2 F) in the last hundred years. Rate of warming has doubled in the past 50 years.
Predictions indicate future accelerated & extreme warming.
IPCC 2007: WG1-AR4
IMPLICATIONS OF WHAT WE KNOW Warmer temperatures mean:
Longer growing season Desiccation due to warmingAltered hydrologic cycle
atmosphere holds more water vapor intense rainfall eventstiming (altered seasonal precipitation; earlier loss of snow pack)some regions will experience more drought
Photo: Sam Cox
How will climate change be expressedat local and regional scales?
How will rangelands respond to increasedoccurrences of extreme events?
How will rising CO2, warmer temperature and altered pre-cipitation affect rangelands?
How will rangelands & rangelandmanagers adapt to a more variable environment?
Areas of Uncertainty weather, climate rangeland responses
How will climate change be expressedat regional and local levels?
Photos: Cox, Derner & SGS LTER
OBSERVATIONAL INFORMATION: Historical records & correspondences of early explorers & settlers.
Caption from Barker et al., 1934 speaks of “ Coronado and hisBand …wandering across … burning sands”, but the expeditions journal of 1541 recorded not deserts but grasslands. (Hart and Hart. 1997. Rangelands 19:4-11)
OBSERVATIONAL INFORMATION: Photographs can provide additional qualitative information
Honey locust tree islands in Kansas Tallgrass Prairie.Present-day encroachment?Fire removal, climate change, CO2?(photograph courtesy of Alan K. Knapp).
Mesquite encroachment in SWover past two centuries
(photograph courtesy of ARS Jornada Experimental Range photo gallery).
OBSERVATIONAL INFORMATION: Quantitative monitoring for management purposes may be especially useful for climate change
Aerial photography & imagingsoftware for quantifying range condition. High resolution infor-mation for assessing rangelandecological services.
Booth, Cox & Simonds
Observation Combined with Experimental Treatments Over Time Can Be Powerful
Derner & Schuman. 2007. Jour. Soil & Water Cons. 62:77-85
0-10 ka Bignell Loess
10-13 ka Brady Soil
13-23 ka Peoria Loess
% C4 Vegetation
Warmer/dry C4 grasses
Cooler/wet C3 shrubs & grasses
Kelly and Busacca, in Prep
Plants leave geochemical fingerprints in soils !
Observational Information
• Information on ecosystem attributes, obtained in realistic environments, oftentimes of considerable time lengths
• Information is often complicated by other factors, like management, which have changed over time
• Interpretations often speculative • Limited information on future
environments, including multiple changes
Manipulative Research for Assessing Ecosystem Responses to CC
Free Air CO2 Enrichment in MojaveIR Warming on Tibetan Plateau
Precipitation manipulation in Kansas tallgrass
Mostly single factorexperiments
Run for two to several years
Photos: Nowak, Wang& Knapp
Open Top Chamber CO2 Enrichment Work on the Colorado Shortgrass Steppe: 1996-2001
USDA-ARS & Shortgrass Steppe LTER
Doubling Ambient CO2: • Increased NPP 44%• Increased plant WUE• Favored some plant spp. over others• Forage N and forage quality declined
CO2-production responses
• cool-season, C3 grasses • fringed sage, 40-fold
Prairie Heating and CO2 Enrichment (PHACE)Cheyenne, Wyoming, USA (summer, 2008)
ACN AHN ECN EHN ACIs ACId
PHACE EXPERIMENTAL TREATMENTS
CO2 A (present ambient, 380 ppm), E (elevated, 600 ppm)TEMP C (present temp), H (+ 1.5/3.0 C day/night)IRRIG Is (several seasonal water additions), N (non-irrigated)IRRIG Id (one or two annual water additions)
2 CO2 by 2 TEMP factorial (5 reps each) 2 IRRIG Trts (5 reps each)
Ambient CO2
Ambient tempNo irrigation
Ambient CO2
High temp No irrigation
High CO2
Ambient tempNo irrigation
High CO2
High TempNo irrigation
Ambient CO2
Ambient tempShallow irrigation
Ambient CO2
Ambient tempDeep irrigation
ACN AHN ECN EHN ACIs
ACId
PHACE EXPERIMENTAL TREATMENTS
CO2 A (present ambient, 380 ppm), E (elevated, 600 ppm)TEMP C (present temp), H (+ 1.5/3.0 C day/night)IRRIG Is (several seasonal water additions), N (non-irrigated)IRRIG Id (one or two annual water additions)
High CO2
Ambient tempNo irrigation
Ambient CO2
Ambient tempShallow irrigation
Does water replacementgive the same response as elevated CO2?
Prairie Heating and CO2 Enrichment (PHACE) Experiment (Cheyenne, WY, USA)
Direct Responses to GC Factors
Indirect Effects of Water
CO2 ring
SentekSWC
Trace gas exchange
Root dynamics
Plant species abundancesCanopy photosynthesis
Manipulative Experiments
• Can expose plants and plant communities to altered environmental conditions
• Can provide mechanistic information (NOT considered simulations of the future)
• Manipulations artificial, often with known and unknown artifacts
• Costly
• Few multiple GC experiments
Modeling
• Mathematical representations of reality– empirical (based on observation; practical)– theoretical (based on mechanisms)
• Useful for understanding how systems function
• Can fill in knowledge gaps
• Predictive tools
Epstein, Gill, Paruelo, Lauenroth, Jia and Burke. 2002. J. of Biogeography 29:875-888
Modeled Future Relative Abundances in Temperate Grasslands of North & South America. Based on: • GCMs • Relative Abundance Equations
Based on observations & measurements obtained in the real world.
Empirical relationships may not capture CO2 response
Plant Community Modeling
Summary
• Observation, manipulation, & modeling: useful tools for studying climate change and impacts on rangelands
• The complexities and uncertainties of climate change argue strongly for – utilizing all of these in our predictions– accepting that policy and management
decision will always rely on a certain amount of uncertainty
Summary
• Science can help us understand & deal with that uncertainty– weather forecasting, monitoring and decision
support systems can help us cope with an increasingly uncertain world
– learning from other regions/countries where today we may find examples of our future climates (e.g., Australia in terms of variable weather)
THANKS FOR YOUR ATTENTION
2008 SUMMER BIOMASS FIELD CREW