Transcript PPT - Atmospheric and Oceanic Sciences

AOS 101
Climate Change:
Introduction
March 4/6
100
BIG PICTURE
heat budget of earth and atmosphere
30
SPACE
12
58
ATMOSPHERE
20
Shortwave
50
Longwave
102
7
94
GROUND
Conduction
Convection
23
Latent
Heat
“GREENHOUSE” EFFECT
12
58
CH4 N2O
CO2
H2 O
102
Longwave
94
• 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
radiation back to the earth.
• More trace gas  More
atmospheric emittance  More
energy re-absorbed by the
earth  Warmer temperature
GROUND
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.