The Anthropogenic Greenhouse Effect Anthropogenic Greenhouse Effect The

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, CO 2 - Methane, CH 4 - Nitrous oxide , N 2 O - Halocarbons These do NOT exist naturally. They are additional GH gases - Ground Level Ozone 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: UV ozone (O 3) oxygen (O 2) • UV rays can cause skin cancer and cataracts. • CFC’s act as a catalyst to speed up the breakdown of O 3: CFC ozone (O 3) oxygen (O 2)

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 (CO 2) methane (CH 4) nitrous oxide (N 2 O) hydrofluorocarbon (HFC) = = = 1 (least potent) = 25 298 14, 800

Why Focus on Carbon? • CO 2 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 1800 s. • Fossil fuel extraction and combustion also releases N 2 O and CH 4.

Ground Level Ozone • A major component of smog. • Produced by photochemical reactions between N 2 O and volatile organic compounds in the presence of sunlight. 13

Ground Level Ozone • 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