the anthropogenic greenhouse effect. anthropogenic greenhouse effect “the enhancement of the...
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The Anthropogenic Greenhouse Effect
Anthropogenic Greenhouse Effect
“The enhancement of the natural greenhouse effect due to human activity.”
The Problem:• The increase in greenhouse gas levels may
trap more IR in the atmosphere, increasing the average global temperature.
Greenhouse Effect Comparison
Anthropogenic Greenhouse Gases
• Humans have little effect on water vapour since it moves rapidly through the water cycle.
• Humans are increasing the levels of:- Carbon dioxide, CO2
- Methane, CH4
- Nitrous oxide , N2O
- Halocarbons- Ground Level Ozone
These do NOT exist naturally. They are additional GH gases added by humans.
Carbon Dioxide
Sources:• Combustion of fossil fuels.
– Transportation, heating, generating electricity, etc.
• Burning forests to clear land.• Cement making.
Methane
Sources:• Coal and natural gas processing.• Agriculture (manure).• Landfill sites (garbage).
Nitrous Oxide
Sources:• Combustion of fossil fuels.• Chemical fertilizers.• Manure and sewage.
Halocarbons
• Synthetic compounds containing carbon and halogen elements (F, Cl, Br).
• Used as cleaners, solvents, and coolants.
• Includes CFCs (chlorofluorocarbons).
CFCs and the Ozone Layer
• The ozone layer in the stratosphere absorbs harmful ultraviolet radiation:
UVozone (O3) oxygen (O2)
• UV rays can cause skin cancer and cataracts. • CFC’s act as a catalyst to speed up the
breakdown of O3:CFC
ozone (O3) oxygen (O2)
CFCs and the Ozone Layer
• CFCs banned since 1989.• Replaced by other halocarbons... but ALL
halocarbons also absorb IR radiation and act as greenhouse gases too!
Global Warming Potential (GWP)
A measure of the ability of gases to trap (absorb) IR radiation.
carbon dioxide (CO2) = 1 (least potent)methane (CH4) = 25nitrous oxide (N2O) = 298hydrofluorocarbon (HFC) = 14,800
Why Focus on Carbon?
• CO2 has a low GWP but it is the most abundant greenhouse gas.
• It is also a greenhouse gas that humans directly impact on a large scale.
• Fossil fuel use has increased exponentially since the 1800s.
• Fossil fuel extraction and combustion also releases N2O and CH4.
Ground Level Ozone
• A major component of smog.
13
• Produced by photochemical reactions between N2O and volatile organic compounds in the presence of sunlight.
• Higher levels occur from May to September, between noon and early evening.
• Very harmful to environment: damages plants and severe respiratory health problems in humans and other animals. 14
Ground Level Ozone
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