CHAPTER 3
Which greenhouse gases are the most important?
Depends on their concentration in the atmosphere
Depends on the strength of their absorption of infrared radiation

CO2 is the most important of the greenhouse gases that are increasing in atmospheric concentration because of human activities.
The increase in CO2 has contributed to about 72% of the enhanced greenhouse effect to date, methane about 21% and nitrous oxide about 7%.

Radiative forcing – the change in average net radiation at the top of the troposphere which occurs because of a change in the concentration of a greenhouse gas or because of some other change in the overall climate system

Positive radiative forcing – on average warms the surface
Negative radiative forcing – on average cools the surface

CARBON CYLE
CO2 provides the dominant means through which carbon is transferred in nature between many natural carbon reservoirs.

- We contribute to cycle when breathing.
- Carbon from our food is burnt & turned into CO2 that we then exhale; in this way we are provided with the energy we need to maintain our life - Animals contribute in the same way - Fires also - Rotting wood & decomposition of organic material in the soil & elsewhere

PHOTOSYNTHESIS works in the opposite way
Plants and trees, in the presence of light, take in CO2, use the carbon for
Growth & return the oxygen back to the atmosphere
Photosynthesis & respiration also occur in the ocean.

Biota – covers all living things

The various reservoirs in the carbon cycle: the atmosphere the oceans (includes ocean biota) the soil & land biota (biosphere)

The movement of carbon in the form of CO2 in and out of the atmosphere are quite large. @ 1/5 of the total amount in the atmosphere is cycled in & out each year. partly through the land biota & partly through physical & chemical processes across the ocean surface.

The land and ocean reservoirs are much larger than the amount in the atmosphere. small changes in large reservoirs could have a large effect on the atmospheric concentration.
The release of just 2% of the carbon stored in the oceans would double the amount of atmospheric CO2.
Lifetime of about 100 years id quoted for atmospheric CO2

Before human activities became a disturbance, exchanges between reservoirs were constant.
Steady balance was maintained before industrialization
Since then, over 600,000 tonnes of C have been emitted from fossil fuel burning
Concentration of CO2 in atmosphere increased by 36%

Most of burnt fossil fuels is used to provide heating & domestic appliances, for industry and transport
90’s – emissions rose @ .7% and between 99-05, rose @ 3%

Since @ 40% of the new carbon remained to increase the atmospheric concentration, the other 60% was taken up by the oceans and land biota.

@95% of fossil fuel burning happens in the northern hemisphere, meaning there is more CO2 there.

CO2 dissolves in water.
Water and air above it exchanges CO2 continually.
Particularly as waves break
Equilibrium is established between the concentration of CO2 dissolved in the surface waters & concentration in air above surface
If atmospheric concentration changes by 10%, the concentration in water changes by only 1%
This change will occur rapidly in upper waters, but it takes longer in lower water
Ocean is not an immediate help for atmospheric CO2

Solubility pump – process when CO2 is gradually drawn from the atmosphere into the ocean’s lower levels

Biological activity in oceans play important role.
Oceans are teeming with life.
Living material in oceans is produced at some 30-40% of the rate of production on land
Mostly plant life and animal plankton
As they die/decay some of the carbon they contain is carried downwards into lower levels of ocean adding to the carbon content of those levels
Biological pump – process where CO2 in atmosphere is dissolved in sea water where it is used for photosynthesis by