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Climate Change: Science Basics
and Impacts Around the
Great Lakes
Jeffrey 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, future impact poorly understood
About 10 days
Carbon
Dioxide
Methane
Fossil fuel consumption,
deforestation
Ag byproduct; fossil fuel
extraction
Car combustion; it is part of
photochemical smog
100-500 years
Decay of fertilizers; car
exhaust
Aerosol sprays pre-1990s
114 years
Ozone
Nitrous
Oxide
CFC’s
12 years
Hours/days
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 19912005)
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
1900-1910
2000’s
Dayton: 6 days
Columbus: 4.5 days
Cleveland: under 4 days
Dayton: 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 event
illustrating where the lake effect clouds and
precipitation typically occur.
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.
HadCM2 model
Reductions in
Lake-effect
snowfall
Current Lake-effect snowfall
Study conducted by Kunkel, Westcott, Kristovich; Illinois State Water Survey
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.