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31 Oct 2010
Chapter 14
Climate: an area’s long-term atmospheric conditions
Global climate change: trends and variations in Earths climate, involving temperature, precipitation,
and storm frequency and intensity
Global warming: an increase in Earths average surface temperature
- Sun, atmosphere and oceans determine Earths climate
Sun supplies energy atmosphere, clouds, land, ice, and water absorb 70% of insolation, reflecting 30%
- absorbs incoming short-wavelength solar radiation
- surface materials increase in temperature and emit infrared radiation (radiation with longer
wavelengths than visible light)
Greenhouse gases (GHGs)/radiatively active gases: water vapour, ozone (O3), carbon dioxide (CO2),
nitrious oxide (N2O), methane (CH4) and halocarbons absorb infrared radiation
- Reemits infrared energy of different wavelengths
- Some is lost to space, some returns warming the troposphere/surface (greenhouse effect)
- Human activities (anthropogenic) increased concentrations of GHGs over 250-300 years
- Global warming potential: the relative ability of one molecule of a given greenhouse gas to
contribute to warming
- carbon dioxide is most abundant, most potent GHG
- decay of organic material volcanoes
Carbon is sequestered in the lithosphere deposition, partial decay, and compression of organic matter
- Burned fossil fuels faster than can be replenished, cleared/burned forests
- increased methane tapping into fossil fuel deposits, raising livestock that emit methane as a
metabolic waste product, disposing of organic matter in landfills, growing certain crops (rice) risen
250% since 1750
- nitrious oxides feedlots, chemical manufacturing plants, auto emissions, synthetic nitrogen
fertilizers risen 18% since 1750
- ozone UV filter, radiatively active gas risen 36% since 1750
- water vapour contributes most to greenhouse effect
Radiative forcing: amount of change in energy that a given factor causes
- Positive forcing Æ warms, negative forcing Æ cools
Other factors influencing climate
Milankovitch cycles periodic changes in Earths rotation and orbit around the sun
- Wobbling of Earths rotational axis
- Tilt of the axis
- Change in the shape of Earths orbit around the Sun
Solar output the Sun varies in the amount of radiation it emits over short/long timescales
Ocean absorption oceans absorb CO2 slower than it is added into the atmosphere
Ocean circulation cooler water is denser than warmer water so cool water at the poles sink while
warmer surface water surfaces
Thermohaline circulation: a worldwide current system in which warmer, fresher water moves along the
surface and colder, saltier water (more dense) moves deep beneath the surface
Paleoclimate: evidence about climate in the geologic past
Proxy indicators: types of indirect evidence that serve as proxies or substitutes for direct measurement
Stable isotope geochemistry: the study of the behaviour of isotopes that is not radioactive
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