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AOS 101
March 4/6
Climate Change:Introduction
BIG PICTUREheat budget of earth and atmosphere
30
100
20
50
102
12
94
58
7 23
Conduction Convection
Latent HeatLongwave
Shortwave
GROUND
ATMOSPHERE
SPACE
102
12
94
58
GROUND
Longwave
“GREENHOUSE” EFFECT
• Very little of the Earth’s LW escapes to space.
• Most is absorbed by atmospheric trace gases: H2O, CO2, CH4, N2O.
• These gases then RE-EMIT RE-EMIT radiation back to the earth.
• More trace gas More atmospheric emittance More energy re-absorbed by the earth Warmer temperature
H2OCO2
CH4 N2O
Causes
• CO2 (most important GH gas) has increased – from 280 ppm to 379 ppm since Industrial Revolution– mainly from fossil fuel use
• Methane and N2O have increased as well due to agriculture/fossil fuels
• Aerosols (e.g. dust) have increased but this would likely lead to cooling.
• Variability of incoming solar radiation may also be a factor.
Feedbacks
• Positive (Self-amplifying) feedback: – an increase will lead to a further increase
through some process.– Population increase = birth rate increase
• Negative (Self-limiting) feedback:– an increase will lead to a decrease back to the
initial state (homeostasis).– Body temp warms = sweating = cooling
Positive Feedback in the Atmosphere:
• Warming earth causes melting of snow/ice = decrease in earth’s albedo (more SW absorbed) = even warmer temperatures
Negative Feedback in the Atmosphere:
• Warming earth causes more clouds = increase in earth’s albedo (less SW absorbed) = temperature stays nearly the same
The fear is that global warming will result in a positive feedback which cause temperatures to increase very rapidly.
Direct Observations of GW
• Eleven of the last 12 years rank as the 12 warmest on record (globally).
• Atmospheric water vapor has increased.• Oceans have warmed.• Snowpack/glaciers are melting.• Sea levels have risen 15-20 cm over the
last century due to expansion and melting.
Arguments against
• Correlation does not imply causation.• Natural variability has caused similar
magnitude changes in the past.• Data:
– temperature data begins ~1800 (end of little ice age)
– reliability of tree rings/ice cores (only account for certain regions).
Projections (*IPCC)
• 1.1o-6.4oC increase in global temperature over the next century
• Permanent Arctic ice may disappear by 2100.
• Hot extremes, heat waves, heavy precipitation more common.
• 20-60 cm sea level rise by 2100.
Decisions
• ADAPTATION– Accept warming planet and make
changes as problems arise.
• MITIGATION– Try to reverse climate change to
prevent negative effects.
• Both will cost money.