I. The Greenhouse Effect

A. Review of Greenhouse Effect - absorption of radiated long-wave energy by Gases and aerosols in the atmosphere

B.Human action is adding to the greenhouse effect by increasing the concentrations of greenhouse gases and aerosols through:

1.industrial activity (burning of fossil fuels) 2.deforestation 3.releases of chlorofluorocarbons

A. Ultimate effects of human activity is still controversial

1.what will happen to climate globally and regionally?

a.temperature response? b.Rainfall patterns?

2.what will be the effect on ecosystems - both natural and agricultural? 2.What are the political, social, and economic consequences?

A.Greenhouse gases

1.carbon dioxide -

a.increases over last few decades b.increases over last few centuries

2.nitrous oxide

a.contributes to a minor extent to destruction of ozone in stratosphere b.trends in time

3.methane -very effective greenhouse gas

a.trends in time

4.chlorofluorocarbons - exclusively of industrial origin

a.responsible for ozone depletion b.in small quantities but highly chemically reactive and long-lived c.trends in time

5.ozone -

a.natural sources - electrical storms, decomposing plants, fires b.important greenhouse gas - absorbs uv radiation c.occurs in troposphere and stratosphere d.a pollutant in the troposphere (responsible for smog - toxic) e.in stratosphere it filters out 99% of uv radiation - acts as a protective shield against ionizing radiation f.trends in time g.most dramatic effects have been in the Antarctic - circumpolar winds then collect, trap, and concentrate CFCs delivered to this part of the planet from high latitudes. During period of sunlight, CFCs are photochemically activated and breakdown ozone layer h.Montreal Protocol of 1987 - resulted in worldwide decrease in production and use of CFCs

6. water vapor - the principal greenhouse gas

a.although amount of water in atmosphere is not increasing - global warming from increases in other greenhouse gases could lead to enhanced evaporation and increases in water vapor

A.Geographic Distribution

1.CO2 is responsible for about 60% of human-enhanced greenhouse effect

2.Geographic distribution of carbon dioxide emissions

3.Methane is associated more with plantation agriculture, especially rice production

A.Potential Effects - widely debated

1.global warming - how much? Has it begun? How should we respond?

2.Record of land-based temperature since 1861

3.1980s and 1990s have been warm decades

4.Middle troposphere records indicate cooling of atmosphere during this same period

5.Intergovernmental Panel of Climate Change (IPCC) estimates of future warming -almost all work on predictions involves global climatic models (GCMs) the validity of which is largely unknown

6.Changes in sea level - difficult to estimate but could have catastrophic consequences - many people live around the world live in environments only a few cm above current sea level

7.Summary - general concensus among atmospheric scientists is that details of global warming are unpredictable, but that overall warming is highly probable

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