Climate Change

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

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 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

Also: Manure

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

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!

Stratospheric Cooling Why ? Ozone depletion Tropospheric [CO2] increases

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 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