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Chapter 9

ESS102H1 Chapter Notes - Chapter 9: Global Warming Potential, Black Carbon, Radiative Forcing

Earth Sciences
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[GLG Text Notes Chapter 9-10] 1
Chapter 9: Global Climate Change
Climate: describes an area’s long-term atmospheric conditions, including temperature, moisture
content, wind, precipitation, barometric pressure, solar radiation, and other characteristics
o Climate differs from weather in that weather specifies conditions localized sites over
hours or days, whereas climate describes conditions across broader regions over
seasons, years, or millennia
o Global climate change: describes trends and variation in Earth’s climate, involving
aspects such as temperature, precipitation, and storm frequency and intensity
Global warming: refers to change in average global surface temperature
Three factors exert more influence on Earth’s climate than all others:
o Sun (provides heat + energy)
o Atmosphere (keeps a habitable temperature; moderates temp)
o Oceans (shape climate; stores + transports heat and moisture)
Greenhouse gases such as nitrous oxide and carbon dioxide absorb and re-emit infrared
radiation, some of which travel into space while others are projected downward back to the
surface thus warming the surface known as greenhouse effect
Global warming potential refers to the relative ability of one molecule of a given greenhouse
gas to contribute to warming
Carbon dioxide is the greenhouse gas of primary concern: although it does not have most
potential, its abundance in the atmosphere makes it the most significant; human activity has
boosts its concentration in the atmosphere; burning fossil fuels add CO2
o Other greenhouse gases also add to warning: methane by tapping into fuel deposits,
nitrous oxide is by-product of chemical manufacturing plants, water vapour (it is not
view as having driven industrial-age climate change because its global concentration has
not changed)
Aerosols: microscopic droplets and particles, can have either a warming or cooling effect; e.g.
soot or black carbon aerosols can cause warming by absorbing solar energy, but most
phosphoric aerosols cool the atmosphere by reflecting the sun’s rays
The amount of change in energy that a given factor causes is called its radiative forcing
o Positive forcing warms the surface, whereas negative forcing cools it
o Currently, Earth is experience an overall radiative forcing of 1.6 watts per m2
Other factors that influence the climate, besides the composition of the atmosphere:
o Milankovitch cycles: three periodic changes in Earth’s rotation and orbit around the sun
which alter the way solar radiation is distributed over the Earth’s surface
o Solar output: 11-year sunspot cycle; radiation emitted by sun various over short and
long time scales; however, it is concluded that it does not have enough change to drive
significant temp change on Earth’s surface
o Ocean absorption: oceans absorb the CO2 but are absorbing at a slower rate than
humans are adding it; also, as oceans are warmed it slows down even more at
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