Global Warming Part I

Greenhouse Effect

Shown above is an Infrared Map of the Earth. Red areas represent regions of high heat retention in the atmosphere. This is an equatorial band because that is where the atmosphere has the most water vapor.

The earth has a natural greenhouse effect due to trace amounts of H20 and CO2 that naturally occur. The enhanced greenhouse effect refers to the augmentation of these natural gases by human activities.

What's the evidence?

The energy balance in the atmosphere is shown here:

The main components in this diagram are the following:

What Happens to the 69% of the incoming radiation that doesn't get reflected back:

Achieving Thermal Equilibrium:

This short wavelength radiation is absorbed by the earth which heats the earth to a finite temperature. Since the earth wants to stay in thermal equilibrium, it must re-radiate this energy.

The earth has an equilibrium temperature of about 300 Kelvins . At this temperature, the wavelength of the emitted radiation is in the infrared.

What happens to the outgoing infrared radiation?

So clearly, if human activities increase the ability for the earth's atmosphere to absorb IR radiation, this produces a net warming of the atmosphere over time. This is the Enhanced Greenhouse effect:

 

Table 1

Characteristics of some major (climate changing) greenhouse gases

Greenhouse gas

Sources

Sinks

Importance for climate

Carbon Dioxide

(CO2)

1) Burning of fossil fuel

2) Land-use change (deforestation)

1) Ocean Uptake

2) Plants!& photosynthesis

Absorbs infrared radiation; affects stratospheric O3

Methane

(CH4)

1) Biomass burning

2) Enteric fermentation

3)Rice paddies

1) Reactions with OH

2) Microorganisms uptake by soils

Absorbs infrared radiation; affects tropospheric O3 and OH; affects stratospheric O3 and H2O; produces CO2

Nitrous Oxide

(N2O)

1) Biomass burning

2) Fossil-fuel combustion

3) Fertilizers

1) Removal by soils

2) Stratospheric photolysis and reaction with O

Absorbs infrared radiation; affects stratospheric O3

Ozone

(O3)

Photochemical reactions involving O2

Catalytic chemical reactions involving NOx, ClOx and HOx species.

Absorbs ultraviolet and infrared radiation

Carbon Monoxide

(CO)

1) Plant emissions

2) Man-made release (transport, industrial)

1) Soil uptake

2) Reactions with OH

Affects stratospheric O3 and OH cycles; produces CO2

Chlorofluorocarbons

(CFCs)

Industrial production

Insignificant in troposphere, dissociated in stratosphere (photolysis and reaction with O)

Absorbs infrared radiation; affects stratospheric O3

Sulphur Dioxide

(SO2)

1) Volcanoes

2) Coal and Biomass burning

1) Dry and wet deposition

2) Reactions with OH

Forms aerosols, which scatter solar radiation

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