- The sun was 30% dimmer when life began, but this has had very little effect on Earth’s temperature.
- Why has Earth’s temperature not changed as the sun heated?
- The Earth used to have way more CO2.
- As time went on, CO2 was depleted by erosion (weathering/erosion includes a chemical reaction that removes CO2), and later by life (plants) on Earth.
- The two factors have roughly balanced each other out.
- We can measure ancient temperatures using isotope ratios in rock samples.
- Lighter isotopes move more when it’s hotter and therefore are less present in rocks/ice.
- Pavement gets heated up, then the UV light it emits can’t escape due to the greenhouse effect.
- CO2 is not the most powerful greenhouse gas - H2O is.
- But, small changes to CO2 levels in atmosphere make dramatic changes to Earth’s temperature.
- Until recently, CO2 in the atmosphere has been in decline.
- Earth has very little CO2 because it’s pulled from the atmosphere (weathering/erosion).
- Having life on a planet regulates CO2 levels.
- Continent placement affects climate.
- If there’s more ice surface area, more sunlight is reflected back out.
- Earth has gone through periodic swings in CO2 levels.
- But our current levels are very much not in normal ranges.
- These swings are due to Milankovic Cycles.
- Eccentricity (orbit is circle or ellipse)
- Obliquity (axis tilt)
- Precession (top of Earth spins like a top)