lec 15 climates of the distant past

trends

patterns of global changes over a longer period of time

rhythms

shorter-term repeating climate cycles

icehouse earth

a period with permanent ice caps, us now

glacial period

when glaciers are growing

interglacial period

glaciers are receding, where we are now (beginning 11k years ago)

snowball earth

when extreme cold can lead to global glaciation

hothouse earth

no persistent polar ice caps present, more common in earth's history and last happened 40 MY ago

examples of climate forcings

amount of radiation or CO2, positions of continents

feedbacks

processes which can amplify or dampen a climate forcing

tipping points

regime changes, states when an irreversible threshold of forcings is crossed

long-term change in solar radiation is driven by

availability of sun's hydrogen fuel and the rate at which it is burned

why was earth still warm when sun was weaker

CO2 was 10% of atmosphere vs 0.04% now

first life was releasing which gas and consuming which gas

methane and CO2

when ocean life formed, it started

photosynthesizing, decreasing CO2 and releasing oxygen

after methanogens died due to oxygen, methane started to

react with oxygen and convert to CO2, further promoting photosynthesis

huronian glaciations caused by

replacement of methane and CO2 with oxygen, and because solar luminosity was weaker

plate tectonics cycle carbon between

the atmosphere and the mantle

continental drift causes

new landmasses to form and ocean currents to redirect

if land is more concentrated at low latitudes

planet absorbs less energy

when ocean currents change due to continent movement

heat transfer changes direction and heat is redistributed differently e.g. opening of the Drake Passage allows cold to stay trapped by Antarctica and South Atlantic warmth cannot penetrate

gulf stream created when

the Isthmus of Panama closed 3MY ago, leading to greater moisture transport to the Northerm Hemisphere, snowfall and then ice cover

eccentricity

extent of orbit's deviation from a circle in a 100k year cycle

obliquity

earth's rotation on an angle with respect to the orbital plane, affecting the extremes between seasons in a 41k year cycle

precession

tilt direction, gradually rotating with a 26000 year period and changes the season when earth is closes to the sun

milankovic cycles

those that cause changes in the amount and location of solar radiation

high latitude summer insolation

northern hemisphere ice builds up in the winter and only diminished in the summer, while southern is not connected with lower latitudes so ice doesn’t really spread