EES215
Lecture 22
What are potential sinks for CO2?
Role of biosphere - decrease in forests; history of forests in northern,
southern hemisphere.
Consequences of increase in greenhouse gases:
Record of temperature increase
Potential consequences of temperature increase:
There is clear agreement on a pronounced CO2 increase in the
atmosphere, general agreement that it is related to the release from the use of
fossil fuels (coal, oil and gas), and increasing agreement that it has caused
an observable, overall increase in global temperatures. There is much less of a consensus on the
potential consequences, however, leading to quite different future scenarios. Potential consequences include:
melting of icecaps; flooding of coastal areas; higher amount of precipitation;
increase in icecaps; increase (or decrease) in albedo; increase (or decrease)
in temperature; shift in precipitation patterns; shift in wind belts; shift in
ocean currents; stop of deep water formation in the North Atlantic and end to
the thermohaline convection.
Occurrence of gas hydrates
Gas hydrates form by entrapment of methane in ice, found in specific
temperature and pressure range in marine sediments. Typical conditions: water
depths between 1500 and 2000 m on continental slope; between 100 and 500 m deep
in marine sediments; other occurrence in permafrost areas and along continental
shelf in arctic areas (see graphs in Kvenvolden,
1999).
Estimates of total amount of methane found in this form: between 2 and 40x1015
m3; i.e. very large compared to known reservoirs of fossil fuels or
current use of natural gas.
Origin of gas hydrates: dating (using the 129I system) of pore
waters associated with gas hydrates on Blake Ridge shows that iodine (and
probably also methane) originated from formations much older than the current
reservoir formations à large scale
migration of methane from deep sources likely (see graphs in Fehn et al.,
2000).
Ice ages:
Observations - drop in average temperature; increase in amount of ice; ice
coverage in northern; southern hemisphere; history of ice ages; role of CO2
Forcing mechanism: Milankovitch cycle: irregularities in rotation
of earth affect insolation at high northern latitudes - temperatures remain
below zero throughout year - build-up of ice.
Forcing function related to rotation of earth around sun - eccentricity; tilt,
time of prehelion - insolation in northern summer - predicts glacial events at
19,000; 24,000; 43,000 and 100,000 yrs.
Potential problems with theory - 100,000 years not necessarily predicted at
correct time.
End of ice age: flow regime in