Option C: Energy. Greenhouse effect

Transcription

1 Option C: Energy C.5 Environmental Impact: Global Warming Greenhouse effect Natural greenhouse effect: absorption of infrared radiation by natural greenhouse gases (CO 2 and H 2 O vapour) in the atmosphere warming the earth if not surface would be 30K cooler. Anthropogenic greenhouse effect: caused by gases emitted by human activities. 1

2 solar radiation spectrum natural greenhouse effect Greenhouse Analogy:Energy from the sun in the form of some ultraviolet and visible light (short wavelength) passes through the glass of the greenhouse. As the light strikes various surfaces in the greenhouse they are heated. These surfaces in turn re-radiate the heat in the form of infrared radiation (long wavelength). However, the IR radiation is blocked from escaping by the glass. IR is not able to pass through the glass, hence the greenhouse air heats up fairly dramatically. The greenhouse gases have the same property as the glass towards the IR radiation. Think of the greenhouse gases acting as an invisible glass shield around the earth. 2

3 T 1950 present day 3

4 Where will it occur primarily? terminology greenhouse effect= the absorbing of some of the infra-red radiation radiated from the Earth in the atmosphere which is then reradiated back to Earth; this results in global warming= a gradual increase in planet-wide temperatures 4

5 Global warming:evidence Global warming: Historic CO 2 levels Ice core from 2874 m depth, years old Thin slice of ice gas bubbles are dark 5

6 What does ice core data tell us? Global warming: CO 2 emissions 6

7 Global warming effects (1) World wide rise in sea levels resulting from: Partial melting of glaciers and polar ice caps Thermal expansion of water (as a result of heating). Changes in crop yields: some crops will grow better, other worse. Global warming effects (2) Changes in distribution of commercial crops Changes in the distribution of pests and diseasecarrying organisms e.g. malaria. More severe weather conditions: floods in particular of coastal areas; more severe storms e.g. monsoon floods in Pakistan 2010 More severe droughts e.g worst drought in Amazon 7

8 Local effects will differ why? Greenhouse factor Compares ability of a greenhouse gas to absorb IR to the same amount of carbon dioxide which has a factor of 1. Example: greenhouse factor of methane is 30 which means it absorbs as much as 30 molecules of carbon dioxide or 1 molecule of methane absorbs 30 times more as 1 molecule of carbon dioxide. 8

9 Greenhouse gases: H 2 O Sources: Human: combustion of hydrocarbons Natural: evaporation Relative effect: 0.1 -Least effective in trapping radiation but is most abundant. Sources: greenhouse gas: CO 2 Human: burning fossil fuels and wood, forest fires, burning waste Natural: respiration, decay of organic matter, natural forest fires Relative effect: Most important greenhouse gas (50% contribution) because of its great abundance (second largest after water vapour) and the large range of wavelengths over which it absorbs IR. 9

10 Greenhouse gases: CH 4 Sources: Human: cattle farming, rice paddies (wet soil means any organic matter in it is decomposed without oxygen), petroleum and natural gas production. Natural: digestive tracts of ruminants, cattle, bogs or marshes, bacterial fermentation when organic matter is decomposed anaerobically, methane gas is produced. Relative effect: 30 - Low abundance in atmosphere but it is more effective in absorbing infrared radiation, however, its atmospheric lifespan in the atmosphere is short. Greenhouse gases: N 2 O Sources: Human: use of nitrogen based fertilizers Natural: bacterial action Relative effect: 160 -Very effective in absorbing radiation, fairly long atmospheric life. 10

11 Sources: Greenhouse gases: CFCs Human: refrigerators, air-conditioning, aerosols in spraying cans, foaming agents Natural: none!!!! Relative effect: Very effective in absorbing radiation, long atmospheric life but low abundance. Greenhouse gases: SF 6 Human source: electrical insulators Greenhouse effect:

12 Greenhouse gases CO 2 released into the atmosphere combines with water according the equation above, leading to ocean acidification. The inhibits shell growth in animals and causes reproductive issues in fish. Ocean Acidification: CO 2 + H 2 O H 2 CO 3 12

13 Global Dimming The release of particulates into the atmosphere from incomplete combustion of fossil fuel use blocks light. This can lead to a reduction in global temperatures, although with consequences. 13

14 Strategies for Reducing CO 2 Levels Increased energy efficiency Reduced dependence on carbon-based fuels Capture and storage of carbon from fossil fuels. 14

15 Increased energy efficiency Reduced dependence on carbon-based fuels Capture and storage of carbon from fossil fuels. 15