1. Climate
Change

3. Ice core data
Temperature,
CO2 and CH4
are all in
phase
Are the gas
concentrations
a cause or an
effect of
warming or
both ?

4. Source: IPCC

5. Milankovitch Cycles Variation of Earth’s tilt
Variation of Earth’s orbit
Wobble of Earth’s axis
Figure 12.3

7. Source: IPCC

8. 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)
Radiative forcing of CH4 is 21 times that of CO2 on
a per-molecule basis
C6H12O6  3CO2 + 3CH4

10. Natural Sources of Atmospheric Methane
Though natural, emissions of
CH4 from wetlands and hydrates
may increase as a result of warming
Total : 30% (~ Tg CH4/year)

11. 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

12. Did a release of methane from clathrates cause the Late Paleocene
Thermal Maximum?
Source: NASA
briefs/schidt_02/fig1.gif

13. Methane formed several millenia ago is released when permafrost melts
POSITIVE FEEDBACK TO GLOBAL CLIMATE WARMING

14. Anthropogenic Sources of
Atmospheric Methane
Total : 70% (~ Tg CH4/year)

15. Sinks for tropospheric CH4
Reaction with hydroxyl radical (~90%)
Transport to the stratosphere (~5%)
Dry soil oxidation (~5%) +
Total : ~560 Tg CH4/y

16. 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

17. Nitrous Oxide – N2O NH4NO3 → N2O + 2H2O
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

18. Also:
Manure

19. Sources of nitrous oxide
Nitrogen-based fertilisers
Nylon production
Oceans
Manure application and handling
Sewage treatment plants
Catalytic converters
Rainforests
Burning fossil fuels and wood
Atmospheric lifetime of N2O: 150 years

20. Agriculture: 80% of anthropogenic N2O sources
Industrial sources: Remaining 20%

22. 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!

23. Stratospheric Cooling
Why ? Ozone depletion
Tropospheric [CO2] increases

24. STRATOSPHERIC OZONE DEPLETION
CAUSE:
Chlorofluorocarbons (CFC’s)
Chlorine and bromine
molecules are converted
to more active forms on
Polar Stratospheric Clouds
PSCs form within the
POLAR VORTEX

26. 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

27. Many
aerosols
can have
a cooling
effect