Download 10.aos2.global.notes.. - Atmospheric and Oceanic Sciences

Global Climate Change
The sky is falling!
The sky is falling!
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Global Climate Change
• Radiative Equilibrium, Solar and
Earth Radiation
• Atmospheric Greenhouse Effect
• Greenhouse Gases
• Global Climate Change
➡ Predictions: Temperature, Sea Level
➡ Feedback Effects
➡ Alternative Causes
➡ Historical Climate Trends
• Remediation: Greenhouse Gas
Emission Reduction
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Radiative Equilibrium
Absorption
Emission
Radiative Equilibrium: amount of EMR
absorbed equals amount of EMR emitted
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Sun and Earth are both near-blackbodies
Sunlight
I
Terrestrial
radiation
λ
Sun, 6000K: emits mostly visible light
Earth, 255K: emits mostly infrared
radiation
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Atmospheric Absorption
• Earth’s atmosphere is a selective
absorber (not a BB)
➡ Transmits visible light (such as
sunlight)
➡ Absorbs infrared radiation (such as
terrestrial radiation)
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The Atmospheric Greenhouse Effect
S
E
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The Atmospheric Greenhouse Effect
S
E
A
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Greenhouse Gases
• These are gases that are
transparent to visible light,
partially opaque to infrared
radiation
• Earth’s major greenhouse gases:
Water
vapor
Methane
Nitrous
oxide
Carbon
dioxide
CFCs
Ozone
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Global Warming Potential (GWP)
—related to amount of predicted
warming (“radiative forcing”) from a
unit increase in gas concentration
GWPs relative to carbon dioxide:
Carbon dioxide
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Methane
Nitrous oxide
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310
Chlorofluorocarbons 4000–20000
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Water Vapor (H2O)
• Sources
➡ Evaporation of oceans, land surface
water
➡ Anthropogenic emissions
(insignificant)
• Sinks
➡ Condensation, precipitation
Largely out of the control of humans;
at higher air temperatures, water vapor
content is often higher than at lower
temperatures
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Carbon Dioxide (CO2)
• Sources
➡ Aerobic respiration
➡ Outgassing by land and oceans
➡ Fossil fuel combustion
• Sinks
➡ Green plant photosynthesis
➡ Dissolution in oceans
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Carbon Cycle
Atmosphere
Plants
Animals
Fossil Fuel
Land
Oceans
Deep Ocean
Sediments
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Anthropogenic Carbon
Dioxide Inventory
Cement
Production
2%
Deforestation
25%
Fossil Fuel
Combustion
73%
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Methane (CH4)
• Sources
➡ Cellulose digestion/breakdown
➡ Organic decay
• Sinks
➡ Chemical reactions
➡ Soil uptake
Recent rapid increase due to food production
and gas field leaks
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Nitrous Oxide (N2O)
• Sources
➡ Soil bacteria
➡ Oceanic outgassing
➡ Combustion, atmospheric chemical
reactions
• Sinks
➡ Chemical reactions in stratosphere
Very slow increase over time (until
recently); linked to agricultural production
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Chlorofluorocarbons
(CFCs)
• Sources
➡ Industrial/consumer leakage, direct
emission (all anthropogenic)
• Sinks
➡ Chemical reactions in stratosphere
Concentration trend dependent on
production of CFCs and regulation
in developed and less-developed
countries
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Global Change
• Climate change due to anthropogenic
greenhouse gas emissions
• Assume: carbon dioxide mixing ratio
doubles in next 50–100 years
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Sea level rises from:
Polar ice cap melt
Thermal expansion of sea water
Vegetation loss from drought,
weather changes
Uncertainties:
Effect of non-CO2 greenhouse gases with
higher GWPs
Emission forecasts
Feedback effects
Limited numerical forecast models
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Feedback Effects
Enhance
Cause
Effect
Suppress
• Positive feedback: the effects enhance or
reinforce the cause, resulting in increased
effect (the “vicious circle”)
• Negative feedback: the effects suppress
the cause, decreasing the effect (“selfcorrecting” or “thermostatic”)
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Albedo
• Reflectivity of a surface
➡ Higher albedo = less absorption of
EMR
➡ Less EMR absorption = lower
temperatures
Overall albedo of Earth-atmosphere system: 30%
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Feedbacks
• Sea level and ice cover changes
➡ Melting ice delays onset of
atmospheric warming
➡ Rising sea level and receding ice
cover decreases albedo —
enhancing warming (positive
feedback)
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• Water vapor and cloud cover
changes
➡ Warmer air can contain more water
vapor—positive feedback
➡ Cloudiness may increase when water
vapor content increases
• Precipitation patterns altered —
vegetation coverage changes
➡ Affects amount of carbon dioxide sink
capacity
➡ Affects albedo
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Other Possible Causes of
Climate Change
• Sunspot cycle (approx. 22 years
long)
➡ Longer cycle = lower solar intensity
➡ Intensity variation less than 0.5%
• Natural variations in solar activity
(flares, prominences, general
increase/decrease in intensity)
➡ Small and unpredictable
➡ General intensity change usually over
geologic time
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Earth’s Climatological Record
Natural carbon dioxide concentration
and temperature appear correlated…do
humans really affect global temperature?
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Year to Year Variation
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What We “Know”
• Humans are increasing the
atmospheric carbon dioxide content
• About 0.5–1.0°C increase in global
temperature during the last 100
years
• The major greenhouse gas
concentrations will continue to rise
• Increasing greenhouse gas
concentrations tend to warm the
planet
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What is “Likely”
• Scientific analysis shows a high
likelihood of a connection
between anthropogenic increases
in greenhouse gas concentrations
and the observed warming trend
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What is Not Certain
• How much warming will occur in the
future and how quickly
• Feedback of warming on other
climatic features (e.g., precipitation)
and the Earth System
• Need more information about natural
variations, solar variation, impacts of
clouds and land use, relative
contribution of human activities vs.
natural influences, future greenhouse
gas emissions
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Reduction of GH Gas
Emissions and Accumulation
• Why bother?
• Purpose: risk reduction
➡ Decrease fossil fuel usage
➡ Reduce forest clearing
➡ Increase plant biomass (?)
• Carbon dioxide controlled by
these measures, but what about
methane and nitrous oxide?
➡ Difficult—agricultural link
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Non-Fossil Energy
Sources
•
•
•
•
•
•
•
•
Biomass
Nuclear Fission
Geothermal Heat
Solar Heat Collection
Wind Power
Hydroelectric Power
Photovoltaic Cells
Hydrogen Fuel Cells
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Non-Fossil Energy
Sources
•
•
•
•
Biomass
Nuclear Fission
Geothermal Heat
Solar Heat Collection
Heat
Steam
Electricity
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Non-Fossil Energy
Sources
• Wind Power
• Hydroelectric Power
Kinetic energy
Electricity
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Non-Fossil Energy
Sources
[Energy]
Electricity
• Photovoltaic Cells
• Hydrogen Fuel Cells
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Regulated Carbon Markets
• Set emissions quota, divide into
chunks (“emission credits”),
allocate to polluters
• Unused credits can be sold in
open market
➡ Depending on pollutant, ability to
sell or buy may be regulated
• Quota reduced year-to-year
• Subject to political abuse
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Engineering Climate Change
(or Unchange)
• Problem: Carbon dioxide emission
rate exceeds carbon dioxide sink
rate
Natural
Anthropogenic
Natural
Sources
Sinks
• Solutions:
➡ Decrease source rate
➡ Add anthropogenic sinks
➡ Alter the physical environment
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• Carbon Sequestering
➡ Grow biomass, then
bury it deep in the
ground
➡ Pump carbon dioxide
to bottom of ocean,
letting pressure liquify
the CO2
➡ In both techniques,
the point is to keep
the carbon dioxide in
the ground/ocean, and
out of the atmosphere
CO2
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• Altering the physical environment:
Increase planetary albedo
➡ Install mirrors in the atmosphere or on
Earth’s surface
➡ Distribute light-colored dusts in the air
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