Lecture 9 and 10 Flashcards
Anthropogenic influences on climate change, including time and spatial scale
Land use change - instantaneous, regional, comtinental
Aerosols - instantaneous + constant, regional
Ozone depletion - decades, mostly at poles but minor global affect too
Fossil fuels - decades/centuries, global
What is Radiative forcing?
Most commonly used climate change metrics
Measures how the energy balance of the earth-atmosphere system is influenced when factors that affect climate are altered (IPCC)
Concentration of a gas/pollutant is measured…
Molecules per cubic centimetre cm-3
Gas/pollutant densities are measured…
Microgram per cubic metre
What is the history of CO2 on earth?
40% increase from pre industrial
Atmospheric concentration of co2 in 2013 exceeds the natural range over last 650,000 yrs
2000-2010 average growth = 1.9ppm/yr
Primary source is fossil fuels and small contribution of land use change
Methane
Principal component of natural gas
GH effect higher than CO2
Chemically active + has important role forming the tropospheric ozone
Emissions more uncertain than CO2
Principal loss process = chemical destruction (oxidation), inc. sunlight, oxygen, ozone and water vapour
Atmospheric Lifetime = approx 9 years
Methane concentrations
More than doubled since 1800
Rate of increase recently smaller due to leakage control/ changes to oxidising capacity of the atmosphere
Stored in hydrates beneath sediments of ocean floor, if ocean temps increase could be released into atmosphere
Economic interest as new source of power
Methane plumes found in arctic waters from Sonar images
Methane feedback mechanisms
Warming wetland peat
Subsea floor methane hydrate
Melting permafrost
What do methane feedback mechanisms lead to?
Increase of global temperature
How it the tropospheric ozone formed?
Sunlight + nitrogen oxide + volatile organic compounds + water vapour = ozone
Enhanced globally after industrial phase
How does the stratospheric ozone form? (20-50km altitude)
Photodissociation of the oxygen molecule
Require SW radiation
How is the ozone measured?
Satellites, laser beams, high-altitude aircraft, balloon sondes, large air craft, ground base systems
TOMS: total ozone mapping spectrometer
OMI: ozone measuring instrument
What are Dobson units (DU) used to measure?
Total content of ozone in atmosphere (a vertical ‘ozone column’)
If you compress vertical ozone column to standard temp + pressure then a 1 mm thick ozone layer would correspond to 100 DU
Principal steps in ozone depletion
Emissions Accumulation Transport Conversion Chemical reaction Removal
How is stratospheric ozone destroyed?
Catalytic cycles
In the stratosphere, how are reactive halogen gases and ‘reservoir gases’ formed?
CFCs (chemically inert at lower altitudes) broken up by UV light (photolysed) and the halogen atoms react
Where is ozone depletion strongest?
Polar stratosphere - formation of reactive halogens is particularly effective
Conditions for ozone depletion (at the poles)
Low temperatures (formation of PSC) Isolated conditions (chemical processes) Polar stratospheric clouds (reaction on surface of cloud crystals increases destruction efficiency by 100x)
Ozone destruction - at higher latitudes there is…
Lower temperatures which mean less depletion due to slower reactions
At which summit, did the monitoring by TOMs show that the ozone hole was stabilised because of emission reduction?
Rio 1992
The decrease in the stratospheric ozone layer has what effects?
Small cooling effect on global temperatures
Increase in UV radiation - particularly in Southern Hemisphere, caused more skin cancer cases
When is full recovery expected for the ozone?
By 2050 in mid latitudes, Antarctica will occur later
Direct effects of aerosols
E.g.
Eruption of mount Pinatubo 1991
Approx 10km3 material ejected
Noticeable drop in temperatures, called ‘volcanic winter’
Impressive sunsets worldwide
Indirect aerosol effects
Not related to direct interface of the particle with radiation
Important effect = impact on cloud droplet size which affects clouds albedo and amount of precipitation
Further effects = impacts on heterogenous chemistry, cloud condensation processes etc
