Ice core data
Temperature,CO2 and CH4
are all in phase
Are the gasconcentrationsa cause or aneffect of warming or both ?
Figure 12.3
Wobble of Earth’s axis
Variation of Earth’s orbit
Variation of Earth’s tilt
Milankovitch Cycles
Methane Flux and Climate Change
Under saturated conditions, decomposition of organic matter leads to a slow release of CH4 andCO2, instead of a quicker release of CO2
CH4 evolution is the result of decompostion by anaerobic or methanogenic bacteria (Archaea)
Radiative forcing of CH4 is 21 times that of CO2 on a per-molecule basis
C6H12O6 3CO2 + 3CH4
Total : 30% (~100-200 Tg CH4/year)
Natural Sources of Atmospheric Methane
Though natural, emissions of CH4 from wetlands and hydratesmay increase as a result of warming
Clathrates
Ice-like solid with CH4, surroundedby H2O molecules in a lattice
Ices that locked up huge volumes of CH4 in the muck of cold seabedsof continental shelves
Form under cold conditions withhigh pressure
Released under warm conditionsand low pressure
Source: NASAhttp://www.giss.nasa.gov/research/briefs/schidt_02/fig1.gif
Did a release of methane from clathratescause the Late PaleoceneThermal Maximum?
Methane formed severalmillenia ago is releasedwhen permafrost melts
POSITIVEFEEDBACK TOGLOBALCLIMATEWARMING
Sinks for tropospheric CHSinks for tropospheric CH44
• 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 1.3C higher than without methane
• Dissociation of CH4 leads to CO2: climatic forcing not eliminated
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.
Nitrous Oxide – N2O
NH4NO3 → N2O + 2H2O
Nitrogen-based fertilisers
Sewage treatment plants
Burning fossil fuels and wood
Atmospheric lifetime of N2O: 150 years
Sources of nitrous oxide
Oceans
Rainforests
Nylon production
Catalytic converters
Manure application and handling
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!
CAUSE:
Chlorofluorocarbons (CFC’s)
Chlorine and brominemolecules are converted to more active forms onPolar Stratospheric Clouds
PSCs form within thePOLAR 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 increaseH2O vapour concentrations in high latitudes
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