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