http://www.weru.ksu.edu/new_weru/multimedia/storms/big/duststm4.jpg

Ice core data

Temperature,CO2 and CH4

are all in phase

Are the gasconcentrationsa cause or aneffect of warming or both ?

Source: IPCC

Figure 12.3

Wobble of Earth’s axis

Variation of Earth’s orbit

Variation of Earth’s tilt

Milankovitch Cycles

Source: IPCC

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

Anthropogenic Sources of Atmospheric Methane

Total : 70% (~100-200 Tg CH4/year)

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

Also:Manure

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

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 depletionTropospheric [CO2] increases

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

Manyaerosolscan havea cooling effect