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.

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• 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