Climate Change: Science Basics and Impacts Around the

Great LakesJeffrey C. Rogers

Department of Geography and Atmospheric Science Program

State Climate Office for Ohio

The Ohio State University

May 6, 2010

Ohio State University Climate Change Webinar Series

Climate Change & Water Resource Impacts

in the Great Lakes Region

Overview• Scientific basics of climate change associated

with global warming.– The gases, their sources, temporal changes, role in

climate change.

• Currently observed & the Predicted changes in both air temperature and in rainfall intensity.

• Potential changes in Great Lakes precipitation patterns and water levels.

What are Greenhouse Gases?• Greenhouse gases

(i) absorb outward bound infrared radiation from the earth’s surface.

(ii) Delay the return of infrared radiation to space

(iii) warm the atmosphere.

• The “greenhouse effect” modulates radiation in the earth-atmosphere system.

Greenhouse Gases (GHGs)(ranked by importance)

Gas Source Residency in air

Water Vapor

Evaporation from surface, fut- ure impact poorly understood

About 10 days

Carbon Dioxide

Fossil fuel consumption, deforestation

100-500 years

Methane Ag byproduct; fossil fuel extraction

12 years

Ozone Car combustion; it is part of photochemical smog

Hours/days

Nitrous Oxide

Decay of fertilizers; car exhaust

114 years

CFC’s Aerosol sprays pre-1990s Up to 3,000 yr

Increasing GHG Concentrations

N2O Methane

Earth with Greenhouse Gases

With Greenhouse gases (CO2 and H2O vapor) the planet’s average temperature fluctuates around +59ºF.

This is 60ºF warmer than with no greenhouse gases

40F° is contributed by H2O vapor,

20F° by CO2

Our societal debate is whether the observed increases in GHGs will increase the air temperature beyond 59°F, to 60°F, 61°F, etc.

Carina Van Vliet

Aerosols & Sulfate

• Aerosols: Tiny particles & liquid droplets from burning of fossil fuels that also have radiative effects in our atmosphere.

• Sulfates are aerosols from coal & oil burning; they backscatter solar radiation & cool the climate. “Global dimming”.

Attribution of Climate Change to Human Activities

• Modeled climate change (shaded gray) is close to observed variability (black line).

• The climate change is the sum of the “forcings” shown at bottom, producing a net warming.

• Natural forcings neutral.

• Modeled climate: DOE parallel climate model

Meehl et al (2004; J. Climate)

Annual Air Temperature Trends 1900-2006

Rogers, 2010; J. Climate (submitted)

Plants, Crops, & Climate Change

1990 USDA plant hardiness zones (based on 1974-1986 data)

2006 Nat’l Arbor Day Foundation (based on weather service data 1991-2005)

The U.S. Climate Change Science Program (6/19/08)

“…biggest impacts of global warming will come in the form of changes in weather and climate extremes.”

• More heat waves

• Drought more frequent & severe in some regions

• Precipitation will be less frequent but more intense, high rainfall events more common.

Trends in Heavy Precipitation Periods, 1931-1996

• Heavy precipitation events have already increased.

• Consistent with increases in atmospheric water vapor associated with human-caused greenhouse gas increases.

• Precipitation has become less frequent but more intense.

(Kunkel, Andsager and Easterling, 1999)

One Inch Rain Days per Year: Ohio

1900-1910Dayton: 6 days

Columbus: 4.5 days

Cleveland: under 4 days

2000’sDayton: Over 9 days

Columbus: ~ 8 days

Cleveland: ~ 7 days

Alternating rainfall extremes

• Consequences: flooding, property damage, increased fertilizer runoff.

• Old community water/sewer systems may not be able to handle high rain events.

• Consequences: Prolonged dry periods & drought; low soil moisture; reduced lake/stream levels, reduced community water storage; water conflicts.

Great Lakes Hydrologic Cycle

Water input from precipitation (tan arrows) and flow from the basin streams (green) and upstream lakes (purple), plus ground water.

Air temperature (& wind) controls Evaporation (red arrows) that removes water; as does flow out to other Lakes and to the Atlantic (purple).

EPA: http://www.epa.gov/glnpo/atlas/glat-ch2.html

Changes in Great Lakes’ Levels

• Will be driven by temperature, and therefore evaporation, increases.

• In all models, precipitation changes little, within ± 10%.

A basin-wide Lake-effect snowfall eventillustrating where the lake effect clouds andprecipitation typically occur.

Current Lake-effect snowfall

Reductions inLake-effectsnowfall

Warmer winters = less lake-effect snow

• Southern Lakes: snows become rain more often.

• Northern Lakes: Less ice but still cold, lake effect snow still common.

Study conducted by Kunkel, Westcott, Kristovich; Illinois State Water Survey

HadCM2 model

Summary• Earth already has a substantial greenhouse environment,

keeping the planet warmer than it should be.• Current temperature increases appear to be the result of

warming by GHGs and cooling by sulfates.• Expectations for the future emphasize increased number of

extreme events.• Large variations in precipitation.

– More frequent high rain events, flooding & infrastructure strain– Longer dry spells in between, drought, agricultural problems

• Future Great Lakes’ levels may succumb to increased evaporation.

Thank You!

References

• Kunkel, K.E., K. Andsager, and D.R. Easterling, 1999: Long-term trends in extreme precipitation events over the con-terminous United States and Canada. J. Climate, 12, 2515-2527.

• Meehl, G.A., W.M. Washington, C.A. Ammann, J.M. Arblaster, T.M.L. Wigleym and C. Tebaldi (2004). "Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate". Journal of Climate 17: 3721-3727. Wikipedia: global dimming

• Rogers, J.C., 2010: The 20th century cooling trend over the southeastern U.S. Submitted to J. Climate.