AOS 101 March 4/6 Climate Change: Introduction

BIG PICTURE heat budget of earth and atmosphere Conduction Convection Latent Heat Longwave Shortwave GROUND ATMOSPHERE SPACE

GROUND Longwave “GREENHOUSE” EFFECT Very little of the Earth’s LW escapes to space. Most is absorbed by atmospheric trace gases: H 2 O, CO 2, CH 4, N 2 O. RE-EMITThese gases then RE-EMIT radiation back to the earth. More trace gas  More atmospheric emittance  More energy re-absorbed by the earth  Warmer temperature H2OH2O CO 2 CH 4 N2ON2O

Causes CO 2 (most important GH gas) has increased –from 280 ppm to 379 ppm since Industrial Revolution –mainly from fossil fuel use Methane and N 2 O 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 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) 1.1 o -6.4 o C increase in global temperature over the next century Permanent Arctic ice may disappear by Hot extremes, heat waves, heavy precipitation more common 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.