Lecture 11 – Key Points
- Red is irradiated from the Earth, by
- A lot comes out to the atmosphere
where it is absorbed, mostly by
- Once the heat is absorbed, it can be
irradiated out, or some back to earth.
- Back radiation is the greenhouse
- Light passes through, but heat gets
- Greenhouse is natural effect, and has
a significant effect on Earth. With no
greenhouse, our temperature would
- This can change by these 4 key places.
- Incoming solar radiation
- (earth changes orbit, or sun doesn’t send as much)
- Reflected by clouds, aerosols, and atmosphere
- Mostly aerosols will reflect more, causing Earth to be cooler.
- Volcanos will cause Earth to cool due to volcanic ash (aerosols)
- Greenhouse gases
- Surface of the Earth
- Atmosphere with Ocean or land.
Yellow = short wave (light), red = long wave (heat)
Milankovitch cycle: one of three variations in the Earth’s rotation and
orbit around the sun that result in slight changes in the relative amount
of solar radiation that reaches the earth.
There are 3 cycles (a, b, and c)
- These cycles are all different, and will act at different times, so
2 can be warming, and one cooling, etc…
- Earth orbits the sun in an elipse cycle (c)
- Each one effects more or less sunlight
hitting the earth.
1. is natural
2. Can be natural (volcanic ash) or anthropogenic
Yellow = short wave (light), red = long wave (heat) Class
- Most abundant greenhouse gas is water vapour, but
changes very irregularly around the globe.
- CO2 comes from burning of fossil fuels
- Increase is due to burning fossil fuels
- Mauna Loa is where the first CO2 monitor was.
- This is in the middle of the ocean where there isn’t
- CO2 goes up during winter, and down during summer
- CO2 is more abundant in the atmosphere than any other
GHG àincrease in [CO2] = in temperature
Direct measurement is possible for current trends instead of
proxies. Does not show causation
Warming trend, seaonality: land mass in Northern hemisphere >> southern. Northern
summer = more photosynthesis
- We want to think not only about the abundance of GHGs,
but the different types
- There is ppm on the top, and ppb on methane and nitrous
oxide. So here is 1000 times more CH4 and NO2
- Each molecule has a different capacity to absorb heat
- If we set CO2 to 1 (heat capacity)
- CH4 is 25
- NO2 is 300
- So relative strength is important (that’s why water isn’t as important since
it has a low heat capacity, less than one)
- All these happen naturally, but there is a antropogenic effect.
Profs Total effect depends on abundance (see units on Y axis) and warming potential. Setting
CO2 to 1, heat trapping ability/warming potentials are CH4 = 25, N2O = 298,
Some CFC’s = 15,000
- Where is there lots?
- In Earth in sedimentary rock
- Stock in fossil fuels
- In plants/animals
- In the atmosphere
- Net sink of 2 units per year between
atmosphere and ocean
- GPP is photosynthesis
- Resperation from land and forest balances
- Net deforestation and fossil fuel tip the
balance of the others. Without us, there would be 2 going into the atmosphere,
but with us, it is +5 going into atmosphere.
1. Pools: Sedimentary rock >>Oceans >>Fossil Fuels > Soil > Atm: units = g x 10
2. Flows: sources and sinks: g x 10 exp 15 per yr
3. Ocean = net sink +2
4. Missing carbon: atm = +3.2; inputs = .9 + 6 + .1 = 7; outputs = 2; differnce = 5
5. Soil accumulation is a sink: Boreal peatlands may absorbe missing carbon - Increase in CO2 causes and increase in the GHGs, causing more heat to be sent
back to earth.
- Tipping points of Ocean and atmosphere interact is a little more tricky.
- The uncertainty comes mostly from #4
Yellow = short wave (light), red = long wave (h