Ice core data
Temperature,
CO2 and CH4
are all in
phase
Are the gas
concentrations
a cause or an
effect of
warming or
both ?
Source: IPCC
Milankovitch Cycles
Variation of
Earth’s tilt
Variation of
Earth’s orbit
Wobble of
Earth’s axis
Figure 12.3
Source: IPCC
Methane Flux and Climate Change
Under saturated conditions, decomposition of
organic matter leads to a slow release of CH4 and
CO2, instead of a quicker release of CO2
CH4 evolution is the result of decompostion by
anaerobic or methanogenic bacteria (Archaea)
C6H12O6  3CO2 + 3CH4
Radiative forcing of CH4 is 21 times that of CO2 on
a per-molecule basis
Natural Sources of Atmospheric Methane
Though natural, emissions of
CH4 from wetlands and hydrates
may increase as a result of warming
Total : 30% (~100-200 Tg CH4/year)
Clathrates
Ice-like solid with CH4, surrounded
by H2O molecules in a lattice
Ices that locked up huge volumes
of CH4 in the muck of cold seabeds
of continental shelves
Form under cold conditions with
high pressure
Released under warm conditions
and low pressure
Did a release of methane
from clathrates
cause the Late Paleocene
Thermal Maximum?
Source: NASA
http://www.giss.nasa.gov/research/
briefs/schidt_02/fig1.gif
Methane formed several
millenia ago is released
when permafrost melts
POSITIVE
FEEDBACK TO
GLOBAL
CLIMATE
WARMING
Anthropogenic Sources of
Atmospheric Methane
Total : 70% (~100-200 Tg CH4/year)
Sinks for tropospheric CH4
• Reaction with hydroxyl radical (~90%)
• Transport to the stratosphere (~5%)
• Dry soil oxidation (~5%)
+
Total : ~560 Tg CH4/y
CH4 impact on Climate
• CH4 absorbs L↑
• Globally-averaged surface temperature
1.3C higher than without methane
• Dissociation of CH4 leads to CO2:
climatic forcing not eliminated
Nitrous Oxide – N2O
Less than 1/1000 as abundant as carbon dioxide.
296 times more effective at absorbing longwave radiation
4 to 6% of the greenhouse effect enhancement
Denitrication:
Micro-organisms remove nitrogen from the soil and put it
back into the atmosphere
Denitrification produces nitrous oxide.
NH4NO3 → N2O + 2H2O
Also:
Manure
Sources of nitrous oxide
Nitrogen-based fertilisers
Oceans
Nylon production
Manure application and handling
Sewage treatment plants
Catalytic converters
Rainforests
Burning fossil fuels and wood
Atmospheric lifetime of N2O: 150 years
Agriculture: 80% of anthropogenic N2O sources
Industrial sources: Remaining 20%
Chlorofluorocarbons (CFCs) are produced by:
Refrigerators and air conditioners
(CFCs are used as a coolant)
Plastic foams and packaging materials
(CFCs are used as a blowing agent)
Aerosol sprays
(CFCs are used as a propellant)
Manufacturing electronics
(CFCs are used as cleaning solvents)
In addition to ozone layer destruction, CFCs are the most potent
greenhouse gases on a per-molecule basis!
Why ?
Ozone depletion
Tropospheric [CO2] increases
CAUSE:
Chlorofluorocarbons (CFC’s)
Chlorine and bromine
molecules are converted
to more active forms on
Polar Stratospheric Clouds
PSCs form within the
POLAR VORTEX
http://www.cfm.brown.edu/people/sean/Vortex/
Water Vapour
The most important greenhouse gas
Little directional effect from human activities
Strong potential for positive feedback to
global climate warming
How? Global warming would greatly increase
H2O vapour concentrations in high latitudes
Many
aerosols
can have
a cooling
effect