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.