lec 12: Climates Distant Past Flashcards
what is characteristic to ancient climates?
extreme long periods at one of the 2 temperature extremes
what is an ice age?
a period of time where at least some region of the globe is cold enough to form persistent glaciers, so big regions of ice that last more than a season.
what are the 2 states of an ice age?
glacial period: glaciers are growing
interglacial period: glaciers are receding
what is a snowball earth?
a period of extreme glaciation where the entire surface of the earth is covered in glaciers
what is a hot house earth?
no glaciers present
how does a planet make a switch from these extreme temperatures?
3 concepts:
1.climate forcing
2. feedbacks
3. tipping points
what are trends?
global temperature change over a set period of time, generally over long geological time periods
what are rhythms?
repeating cycles of climate, generally shorter on a geological time scale
what is a climate forcing?
factors which have shown to influence global or regional climate
what are feedbacks?
A process which can amplify or dampen a climate forcing (positive vs negative)
What is a tipping point?
the physical or ecological state of an area (or the planet) crosses an “irreversible” threshold of climate forcings
Irreversible on a human scale
on a geological time scale, all climatic changes on earth to date have been shown to be reversible
what changes in the life span of the sun
how much energy it can output, depends on how much hydrogen fuel there is (fusion)
how is energy formed (in the sun)
Hydrogen atoms are forced tgt through intense pressure from gravity (fuse into helium + releases energy)
Helium is heavier than hydrogen = increases pressure at the core = increases rate of hydrogen fusion! [feedback]
has an increase in solar radiation increased global temperature?
it has but not in a significative way
how did solar radiation have a major role in changing temperatures in the global climate distant past?
there was considerably less energy reaching the surface of the earth (less energy to heat the planet)
How could less energy maintain the same average warm temperatures we see globally today?
A change in atmosphere composition! It used to have a much higher carbon concentration (10%) (it’s now around 0,04%)
how was the first atmosphere likely formed?
gases released from cooling planetary rocks kept close due to gravity
what are the later atmospheric influences?
Life and Oxidation
what are the notable features of early atmosphere (3)
- Lack of O2 (and O3)
- High level of CH4
- High level of CO2
how did methane appear?
thanks to methanogens! birth of the organic carbon cycle !
Why does CO2 decrease gradually?
because of the evolution of photosynthesis!
the first ones were bacterias
why did methane decline later on?
the methanogens cannot survive when there is O2, it reacts with O2 and creates CO2
what happens to global temperatures when O2 replaces CH4 and CO2 ?
appears a series of cycles between extreme temperatures (ice ages, glaciation and interglacial periods)
what is the ice-albedo feedback?
positive feedback between ice formation and increasing albedo lowering temperatures
what are some ways in which the planet is a technonically active planet?
- continental drift
- redirection of ocean currents
- new landmasses formed
- carbon is cycled
link plate tectonics and continental drift + the impact
tectonic plates move (producing new crust and recycling old crust)
location of landmass influence:
- ocean currents
- solar radiation budget
- precipitation
link continental drift to ocean currents + impact
global ocean current = transport heat energy (surplus to shortage)
continental drift can isolate or redirect oceanic currents:
1. changes direction of heat transfer
2. eliminate heat transfer region (ex of Antarctica)
link continental drift to solar radiation
angle of insolation and energy distribution
why do equatorial regions have greater rainfall than other lattitudes ?
because it is warmer!
what are the types of movement are linked to orbital processes?
eccentricity
obliquity (tilt angle)
precession (tilt direction)
what is eccentricity?
changing distance between the earth and the sun as the earth orbits the sun
what are 2 things that the orbit path influences?
- solar radiation on earth
- lengths of seasons
what does a greater tilt (obliquity) induce?
greater extreme between seasons
what is precession?
it is the direction of the tilt
what is a Milankovitch cycle?
all changes in Earth’s movement influence climate on a short geological time scale,
during, changes in solar radiation amount and location can change to up to 25%
