Atmosphere

• the troposphere is from ground level to 10km
• the stratosphere extends from 10-50km
• the mesosphere is from 50-80km
• temperature trends fluctuate, but between each layer there is a --pause (e.g: tropopause) where the temperature remains the same despite increasing altitude
• 80% of atmospheric gases are found in the troposphere, with 99.9% being in the stratosphere and troposphere

Remember: tropospheric ozone has bad helath implications including eye irritation and respiratory difficulties, but stratospheric ozone is good because it helps to reduce the damaging UV radiation from reaching Earth

- Gases include N2 (78%) O2 (21%) CO2 (0.04%) rare gases (1%) and O3 (0.000007)

- The concentration of these gases is in a dynamic equilibrium (state of long-term balance with short-term fluctuations) - e.g short changes include daily changes in CO2 due to day/night cycles corresponding with photosynthesis and respiration rates

- nitrogen is needed for proteins, while carbon is the base of all organic molecules. Carbohydrates, lipids and proteins all need carbon in addition to oxygen and hydrogen

- these gases in the atmosphere are responsible for transferring heat across the world, by pressure changes (see atmospheric circulation model) in the air as well as creating ocean currents (North Atlantic Gulf Stream)

- without the atmosphere, Earth would be an average of 33C cooler - less able to sustain life

- greenhouse gases absorb the IR energy emitted from the Earth and re-radiate this in all directions, including back to Earth

Residency time = the length of time the gas exists in the atmosphere reservoir for

Relative effects = the effects per molecule compared to CO2

CO2 - from fossil fuel combustion, drying of peat bogs, ploughng or soils - 1

CH4 - from coalmines, anaerobic respiration, landfill, rice padis - 25

NOx - combustion in the presence of air in vehicle exhausts and power stations - 160 (for NO)

CFCs - used in aerosol propellants, fire extinguishers, coolants, solvents - typically 25 000

Tropospheric O3 - secondary pollutant from photolysis of NO2 and reactions with oxygen - 2000

As shown above, some greenhouse gases have greater greenhouse potential but are released less. This is why CO2 is such a concern, as it has a low potential but in the excessive amounts we release it in currently, it has the greatest warming power

- temperature can affect species directly (eg: corals will lose their zooxanthellae algae)

- precipitation changes could change water availability (think of wetlands - they could dry out)

- increased plant growth could result in dependent species suffering from time errors

- hibernation disruption but lack of food (leads to death by starvation, eg: dormice)

- timing of flowering changes

- changes in species distribution (could lead to migration or simply species loss)

1. wind pattern - affects distribution of heat, and is affected by temperature gradients. Jet streams are growing smaller/weaker

2. rainfall - high evaporation rates lead to more rainfall, but coupled with the different wind patterns, impacts are uncertain - some places could get floods and some droughts

- changes in the cryosphere: increased retreat of glaciers, reduced snow extent, reduced ice thickness, perhaps increased extent of sea ice as land meltwater mixes with saline water and reduces its density so it freezes more readily, more glacial lake floods, changes to flow of seasonal rivers in glacial areas

- weather extremes: more droughts and floods, partially due to increased freq. of El Nino and La Nina weather (from ocean currents) which cause extreme events like these

- sea level rise: due to 2 factors - melting of land ice, thermal expansion of water

Rowland Molina Hypothesis - properties of CFCs that cause ozone depletion

• Persistence - chemically stable so can reach the atmosphere
• Dissociation by UV - emit a free radical Cl atom
• Reactions with chlorine and ozone - free radical can be involved in the breakdown of ozone as well as the prevention of ozone formation

CFCl3 + UV ---> CFCl2 + Cl

Cl + O3 ---> ClO + O2

ClO + O ---> Cl + O2

Destruction of O3 disrupts the dynamic equlibrium in ozone creation and depletion - net loss.

The final reaction prevents monatomic O producing ozone, and releases the Cl free radical to continue damage - this is a cycle that continues

Effects of ozone loss: increased UVB reaching the Earth, resulting in 

• human health issues - increased cases of skin cancer, cataracts, tumours
• damage to plants - leaf tissue damage and reduced photosynthesis
• damage to marine organisms - algae, corals and planktonic organisms affected

MONTREAL PROTOCOL - 2 years after the Vienna Convention (1985) the Montreal Protocol was an international agreement which had legally-binding goals. Main aspects:

• manufacture and use of CFCs and ozone-damaging substances will be phased out & banned
• phase out HCFC use by 2030
• permit the neessary uses of some ODSs (halon fire extinguishers)
• establish a fund to help with implementation of the Montreal Protocol

Key Difficulties:

• time delay between cause and effect
• interconnected systems (jet stream and gulf stream control UK temperature)
• natural fluctuations (e.g: Milankovitch cycles can mask anthropogenic impacts)
• time and spatial scales - difficult to be sure that individual events are part of a longterm trend
• feedback mechanisms and unknown tipping points - to what extent does negative feedback offset positive feedback?
• limited reliability of proxy data for interpreting the climate of the past
• uncertain impacts - species survival is impacted by biotic and abiotic factors; climate also affects population distribution and could fragment it (e.g: flooding being a physical barrier)

1. Flood control - build higher river banks and flood defences like the Thames Barrier floodgates

2. Coastal erosion control - use coastal defences (sea wall, gabions)

3. Managed retreat - controlled flooding of areas involving evacuating the area etc.

4. Urban drainage control - use permeable surfaces to allow infiltration; river flow management can reduce the flow of a higher main river level

5. Adapting buildings - use stils/raised platforms or floating houses

1. Controlling GHGs - through legislation, reducing fossil fuel exploitation, reducing landfill waste, catalytic converters reduce NOx and tropospheric ozone, etc.

2. Carbon Capture and Storage - CCs involves removal of carbon (either pre- or post-combustion), transport, and storage in depleted aquifers, oilfields etc. (underground)

4. Carbon Sequestration - afforestation to increase carbon dioxide removed from the atmosphere. in geoengineering, nutrients can be added to the ocean to increase planktonic growth - they will sink to the bottom when dead and store carbon in sediment

3. Geoengineering - technologies largely untried. Examples include increasing Earth's albedo by painting roofs white, using solar shades in orbit to reduce insolation

Alternative Processes: pump-action sprays negate the need for CFC propellants; stick/roll on deodorants

Alternative Materials:

• HCFCs replaced CFCs but still contain chlorine, so are replaced by HFCs, however they are still greenhouse gases and they are more expensive
• hydrocarbons (propane) replace CFC propellants but are flammable
• safe disposal of CFCs - old fridges and air conditioning units must be drained and incinerated 
• replacements for CFC solvents include alcohols, CO2, HCFCs

Why was the Montreal Protocol (1987) so successful?

- international recognition (role of scientists and evidence)  

- agreement between nearly every country (cooperation)

- development of alternative materials and menthods for ODSs so they were made unnecessary