Chapter 14
Climate: an area’s long-term atmospheric conditions
Global climate change: trends and variations in Earth’s climate, involving temperature, precipitation,
and storm frequency and intensity
Global warming: an increase in Earth’s average surface temperature
- Sun, atmosphere and oceans determine Earth’s 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
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Other factors influencing climate
Milankovitch cycles – periodic changes in Earth’s rotation and orbit around the sun
- Wobbling of Earth’s rotational axis
- Tilt of the axis
- Change in the shape of Earth’s 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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