Elevated CO2 and Ozone:
Causes & Consequences
Bill Holmes
University of Michigan
School of Natural Resources
& Environment
Presentation Outline
• Part I: Rising atmospheric CO2 &
tropospheric ozone
– Sources & trends
• Part II: Impacts on plants & ecosystems
– Research questions, approaches, and
findings
• Part III: Activities
– Calculate your carbon footprint
– View ozone maps, action day alerts
The Greenhouse Effect
Greenhouse Gases
Major Sources of CO2
Global Carbon Budget
Distribution of Emissions
1995 annual totals by region
Carbon Dioxide Information
Analysis Center 2003
Atmospheric CO2 Record
370 ppm
today
299 ppmv, highest in
last 420,000 years
Seasonal Oscillations in
Atmospheric CO2 Concentration
Major Consequences I
• Rising temperatures
– Increase in U.S. of 5-9 ºF by 2100
• Extreme weather
– More frequent heavy precipitation events
– Some regions get drier
• Coastal and permafrost areas vulnerable
– Sea level change
– Storm surges
– Sinking buildings and roads in Alaska
Major Consequences II
• Water quality impacts
– Floods and droughts wreak havoc, especially
in developing countries
• Public health concerns
– Floods, water borne diseases
– Heat stress, air pollution
• Agriculture & forestry impacts
– CO2 promotes productivity, but…
– More droughts, fire, and pest damage
Major Consequences III
• Ecosystem changes
– Climate will change faster than ecosystems
can migrate or adapt
– Changes in plant competition
– Grasslands invade forests in southeast U.S
– Change in disturbance regimes – more fire!
O3 Concentration (ppbv)
Tropospheric Ozone Record
80
60
40
20
0
1870
1890
1910
1930
1950
1970
1990
Redrawn from: Marenco et al. 1994.
J. Geophy. Res. 99: 16,617-16,632
Good Ozone, Bad Ozone
Too little there... CFC’s and halons from air conditioners
and refrigerators break down the protective ozone layer.
Too much here... Vehicles, power
plants and factories emit air pollution
that forms ground-level ozone.
Sources of Ground-Level Ozone
NOx, VOC + sunlight
Ozone
Global Distribution of
Tropospheric Ozone
Tropospheric Ozone Circulation
Effects of "Bad" Ozone
• Human Health
– Coughing, throat irritation, lung damage
– Worse when working or exercising outdoors
• The Environment
– Damages vegetation and ecosystems
– Increases susceptibility of trees to other
stresses (pests, diseases, weather extremes)
– Forest and crop losses
Part II: Impacts on Plants &
Ecosystems
Climate Change
temperature
air pollution
carbon dioxide
ozone
?
Ecosystem Function
plant growth
nutrient cycling
carbon sequestration
Carbon and Nitrogen Cycling in
Terrestrial Ecosystems
Plant
Productivity
Plant Litter
Biochemistry
Soil Nitrogen
Availability
Substrate
Availability
Microbial
Community
Composition & Function
Carbon and Nitrogen Cycling in
Terrestrial Ecosystems
Atmospheric
CO2 & O3
Plant
Productivity
Plant Litter
Biochemistry
Soil Nitrogen
Availability
Substrate
Availability
Atmospheric N
Deposition
Microbial
Community
Composition & Function
Carbon and Nitrogen Cycling in
Terrestrial Ecosystems
Atmospheric
CO2 & O3
Plant
Productivity
Plant Litter
Biochemistry
Soil Nitrogen
Availability
Temperature &
Precipitation
Substrate
Availability
Atmospheric N
Deposition
Microbial
Community
Composition & Function
Free-Air CO2 Enrichment (FACE)
Experiments
Open-air control of atmosphere conditions
Fairly large scale
Longer term than previous chamber
experiments
Major investment of research money
Large teams of researchers
Free-Air CO2 Enrichment (FACE) Sites
Eastern U.S. FACE Sites
Cedar Creek, MN
Rhinelander, WI
Oak Ridge, TN
Durham, NC
Aspen FACE Experiment
Rhinelander, WI
Experimental Design
4 treatments x 3 blocks = 12 rings
ppm CO2:
ppb O3:
Ambient
Control
Elevated
CO2
Elevated
O3
Elevated
CO2 + O3
360
32
560
32
360
56
560
56
Aspen FACE Site
AspenBirch
Aspen
AspenMaple
Why Study Aspen & Birch?
Global Geographic Distribution
(white & stippled areas)
Research Questions
• Will more or less CO2 be sequestered by
forest trees or in soil as CO2 levels rise?
• Will elevated CO2 alleviate other stresses
(e.g. ozone, drought, low fertility)?
• What are the interactive effects of CO2 and
ozone?
CO2 and Ozone Effects
CO2 effects:
+ photosynthesis
+ growth
+ water use efficiency
O3 effects:
– photosynthesis
– growth
+ leaf senescence
Cell-level Ozone Damage
Normal aspen chloroplast
Large starch grains
Intact thylakoid membranes
Ozone damaged chloroplast
Disintegration of thylakoid membrane
Membrane degradation material
Small starch grains
CO2 and O3 Effects on Tree Growth
Aspen
Aspen-Birch
b
b
6000
a
a
a
4000
Foliage
Stems & Branches
Coarse Roots
Fine Roots
Aspen-Maple
b
a
c
ab
a
a
a
2000
CO2 + O3
O3
CO2
Control
CO2 + O3
O3
CO2
Control
CO2 + O3
O3
CO2
0
Control
g m-2
Cumulative Net
Primary Productivity
8000
Research Findings I
• Tree growth increases under elevated CO2 and
decreases under O3
• Carbon sequestration under elevated CO2 is
overestimated in models which do not consider
O3 impacts
• O3 reduces the protective coating of leaves and
damages leaf tissues
• CO2 reduces the damaging effects of O3 and O3 reverses
growth stimulation by CO2
Research Findings II
• Biogeochemical cycling of C and N increases under
elevated CO2, but effects differ among FACE sites
• O3 counteracts most CO2-induced enhancements in
ecosystem processes (soil respiration, N availability…)
• Plant response to CO2 may be limited by N availability or
co-exposure to O3 or other factors.
• Elevated CO2 delays normal autumn leaf senescence,
predisposing some trees to winter dieback
• Aspen and birch insects and diseases increase under
elevated CO2 and O3
Part III: Activities
• What you and your students can do…
– Find ways to reduce CO2 emissions
– Learn about ozone action days
• Get on the web!
– Calculate your carbon footprint
– View ozone maps and action day alerts
Reduce CO2 Emissions
•
•
•
•
Reduce home heating & cooling energy use
Reduce transportation energy use
Increase energy efficiency
Learn about implementation of Kyoto protocol
guidelines in other countries (Canada, UK)
• Carbon offsets: reforestation and forest
conservation programs
Avoid and Reduce “Bad” Ozone
• Check local air quality forecast
– Limit physical exertion outdoors in afternoon
and early evening
• Ozone action days
– Conserve energy
– Avoid driving or filling up fuel tank
– Avoid using lawn mower or other two-stroke
powered equipment
Ideas
• Find and compare different carbon
calculators
• Build your own carbon calculator
• Look up unit conversions
Ex: CCF to therms for natural gas
• Brainstorm ideas for CO2 offsets
• Learn about Kyoto protocol