The Greenhouse Effect

Greenhouse Effect Radiation from the sun easily penetrates the layer of gases surrounding the Earth (the atmosphere) Some of this energy is absorbed by the Earth as heat and some is re-radiated back up into the atmosphere Greenhouse gases in the atmosphere absorb and re- emit infrared radiation which produces a warming effect essential for maintaining liveable temperatures on Earth Greenhouse Effect Video

The Greenhouse Effect

Greenhouse Gases 99% of the atmosphere is made up of nitrogen (N 2 ) and oxygen (O 2 ) neither of these gases contribute to the Greenhouse Effect (don’t absorb infrared radiation) Note: The source of greenhouse gases can be natural, anthropogenic or both. A sink is a process that removes greenhouse gases from the atmosphere.

Sources and Sinks of Carbon

Greenhouse Gases 1)Water vapour 2)Carbon dioxide 3)Methane 4)Ozone 5)Other gases like nitrous oxide Do not copy

Greenhouse gases are listed in green

Greenhouse Gases 1. Water vapour (H 2 O): the most abundant greenhouse gas responsible for 65 – 85 % of the greenhouse effect water vapour is not added to or removed from the atmosphere in significant amounts due to human activity water vapour enters atmosphere through evaporation rate of evaporation depends on the temperature of air and oceans high temperature = higher rate of evaporation

Greenhouse Gases 2. Carbon dioxide (CO 2 ): Sources: a) animal respiration (oxygen inhaled and carbon dioxide exhaled)  natural b) burning of fossil fuels  anthropogenic Sinks: a) Plants remove carbon dioxide from the atmosphere and convert it to stored carbon (found in glucose) during photosynthesis b) Oceans – marine organisms use dissolved carbon dioxide to build shells; eventually forms sedimentary rocks

Greenhouse Gases 3. Methane (CH 4 ): Sources: methane is produced by bacteria that break down waste matter in oxygen- free environments like: - bogs and swamps - rice paddies - digestive system of some animals (ex: cows) - decomposing garbage - processing of coal/natural gas - tanks of liquid manure

3. Methane (CH 4 ): There are no natural methane sinks Some suggested methods to reduce or capture methane: - feeding cattle clover or alfalfa instead of grain - reducing amount of red meat consumed or switching to alternative meats like kangaroo (produce little methane) - putting ‘backpacks’ on cattle that capture the methane produced and then use it as a fuel Greenhouse Gases

4. Ozone (O 3 ): Occurs naturally in the upper atmosphere and blocks harmful UV radiation Ozone can be depleted by addition of gases that contain chlorine Production and use of aerosols containing chlorine is strictly controlled Ground-level ozone comes from vehicle exhaust reacting with sunlight and is a major contributor to smog and ground-level warming

Greenhouse Gases 5. Nitrous oxide (N 2 O): Sources: a) damp, tropical soils and oceans - natural b) produced by bacteria when they break down nitrogen compounds c) chemical fertilizers, manure, sewage treatment, vehicle exhausts – anthropogenic

Greenhouse Gases 6. CFCs (and other halocarbons): Chlorofluorocarbons are purely anthropogenic (no natural sources exist) Use in solvents, cleaners, coolants in fridges and air conditioners last indefinitely in the atmosphere and break apart ozone molecules in upper atmosphere Use has been banned since 1987 in developed countries

Anthropogenic Greenhouse Effect Levels of greenhouse gases (other than water) have increased since about 1750 (Industrial Revolution) some scientists attribute this to: a) burning of fossil fuels b) deforestation c) agriculture d) industrial activities e) pollutants

Greenhouse Gas Concentrations Before and After the Industrial Revolution (See page 329) Greenhouse gasLevel before 1750Current LevelIncrease since 1750 Carbon dioxide280 ppm384 ppm104 ppm Methane700 ppb1745 ppb1045 ppb Nitrous oxide270 ppb314 ppb44 ppb CFCs0 ppb533 ppb

Global Warming Potential (GWP) The contribution of a particular greenhouse gas to global warming depends on: 1)Concentration of gas in atmosphere 2)Ability of gas to absorb heat 3)Length of time gas remains in the atmosphere To compare gases, scientists use a measure, global warming potential (GWP)

Carbon dioxide is assigned a GWP of 1 and all other gases are compared to it Methane  GWP = 25 (takes about 12 years to be broken down and absorbs more heat) Nitrous oxide  GWP = 298 (takes 115 years to be broken down) CFC`s  GWP = (remain in the atmosphere indefinitely and can absorb thousands of times more heat than carbon dioxide) Global Warming Potential (GWP)

Homework p. 326 # 1 p. 332 # 1 – 8