Energy in

Solar energy comes in from the sun. Heat flows out from the deep interior.

• sun’s luminosity changed by 25% over 4B years
• “faint young sun paradox” (“sun is actually dimmer before.”)

Sun spots have an ~11 year cycle, resulting in 0.1 -> 0.2 global temperature change.

Milankovitch Cycles

The eccentricity of the Earth’s cycle wrt sun has increased (cycle become more ovoid).

precession

the axis wrt the earth’s self rotation is slightly rotating

obliquity

the axis wrt the sun’s rotation is slightly rotation

Warming Sources

Multiple sources of global warming.

• carbon dioxide: 69%
• methane: 6%
• nitrus oxide: 5%:

arctic warming faster

albedo

“How much of the energy that’s coming in is absorbed and trapped?”

If there’s no snow or ice, heat would be trapped on Earth. If there is snow or ice, energy will be reflected.

The arctic would then be warming faster.

glacier temperature cycles

gradual cooling: super fast heating.

silicate mineral weathering

300,000 year time scale. Sillicate weathering consumes more CO2. This makes a vicious cycle:

1. weathering increasing results in more consumption of Co2
2. This results in increasing cooling
3. This results in less chemical weathering
4. This results in more Co2
5. which results in more weathering
6. repeating at 1

snowball earth

In 720 and 650 MA, earth was a snowball.

1. because of an extended cold spell, earth starts freezing
2. increased reflectivity results in additional cooling
3. increasing cooling results in build up of co2 in the ocean (since it froze and trap)
4. and thus warming
5. no more snowball earth.