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on which time scales does climate vary?
what is a monsoon?
a seasonal climate oscillation, marked by a reversal of winds and rainfall patterns
why are monsoons important to society?
because some billions of people depend critically on monsoon rains for food
wind patterns associated with asian summer monsoon
from southwest to north east
what is the ENSO?
- atmospheric see-saw pattern between Northern Australia and Tahiti
- an ocean warming along coast of S. america
what is the recurrence time of ENSO events?
why is ENSO prediction valuable to society 1-2 yrs in advance?
because it gives decision-makers some lead time to prepare for its impacts
what is the ultimate cause of the seasonal cycle?
tilt + revolution
why are corals a preferred archive to gain insight into ENSO's past behavior?
- they can live for centuries
- can be accurately dated
- their skeleton incorporates isotopic variations that are closely related to temperature/precipitation changes
what is the North Atlantic Oscillation (NAO)?
a pattern of atmospheric variability defined by the sea-level pressure difference between iceland and the Azores
what creates climate variability?
- internal climate feedbacks (Bjerknes feedback)
- natural climate forcings (sun, volcanic eruptions)
- anthropogenic forcings
ice albedo feedback is an example of
what are 2 examples of negative feedbacks?
- silicate weathering thermostat
- stefan-boltzman law (radiative heat loss increasing with temperature)
what are 3 examples of positive feedbacks?
- water vapor feedback
- ice albedo feedback
- land vegetation-drought feedback
Bjerknes feedback involves mutually reinforcing interactions between
slackening of the trade winds, eastward movement of the pacific warm pool
what controls the carbon cycle on geologic time scales (millions of years)?
volcanic emissions and silicate weathering
since 1950, CO2 has risen in the atmosphere at about ___ the rate of annual fossil fuel consumption
why has CO2 risen in the atmosphere at about half the rate of annual fossil fuel consumption since 1950?
the continental biosphere and the world's ocean offset fossil fuel burning (5.43 GtC/year) by soaking up 3GtC/year
what types of proxy data do scientists use to reconstruct pre-historic climates?
- ice cores
- tree rings
what about deep sea sediment cores informs us about past glacial periods?
d18O of deep-dwelling foraminifera shells records ice volume
the cenozoic is the geologic eon corresponding to the past 65 million years. how do we know the timing of the events that punctuated such a period?
- principle of superposition
- radiometric dating with long-lived nuclides
overall, what happens to the oxygen isotopic composition of the deep ocean over the cenozoic?
- it gets more positive
- it gets heavier
why does the oxygen isotopic composition of the ocean change during the cenozoic?
the lighter isotope 16O is preferentially evaporated from the ocean and stored on land in glaciers, causing the ocean to become isotopically heavier
during which period was the antarctic continent ice-free?
paleocene-eocene thermal maximum
the paleocene-eocene thermal max happened approximately
what are glaciers?
accumulations of snow on land, turning into ice over time
where can we find glaciers today?
what do ice cores record about climate?
- temperature of snow formation
- atmospheric composition
what do antarctic ice cores teach us about climate and CO2?
temperature and CO2 have gone hand-in-hand for the past ~800k yrs
oscillations in global ice volume. pattern: a slow gradual, descent into cold conditions, and an abrupt return to warm conditions. what do we call such warming episodes?
over the past million years or so, what was the average spacing between ice ages?
according to milankovitch theory, what is the pacemaker of the ice ages?
the insolation received at 65N during summer
what determines the average yearly insolation received by a point on earth?
when did the last glacial max occur?
20,000 yrs ago
at the last glacial maximum, a large ice sheet covered much of north america, in particular the northern half of the USA and canada. what was it named?
Laurentide ice sheet
in his AGU lecture, Dr Richard Alley calls CO2 "the biggest control knob" because
it seems to be explaining a large part of global temperature change
did the last glaciation happen smoothly?
no, it was marked by some abrupt cold reversal around 13kya
what defines abrupt climate change?
- faster than the responsible forcing
- too fast for living systems to adapt
2 examples of abrupt climate change
- Younger Dryas
- Dansgaard-Oeschger events
what processes matter for abrupt climate change?
- destabilization of the methane clathrates
- weakening of the thermohaline circulation by freshening
- melting permafrost
what physical notion can help explain the abrupt nature of certain climate events?
climate reconstructions of the past millennium are
quantitative proxy estimates based on a network of well-dated proxy records
which of the following climate events happened in the last millennium?
Little ice age
last glacial max
little ice age
what is the hockey stick controversy about?
whether the current global warmth is unprecedented in the past millenium
amongst the following civilization collapses, which was unlikely to be related to climate change?
the anasazi indians lived in the US southwest, a region presently marginal for agriculture. archeological records indicate that their population peaked around 1100AD, but that their main center was abandoned around 1170AD. what is a likely explanation?
the population peaked before the most severe megadrought of the millennium
what lesson can we derive from the climate-induced collapse of past civilizations?
even advanced societies can break down if climate change overcomes their resilience
the anthropocene is the name given to
the geological era marked by widespread human-caused environmental change
major evolutionary change happened around 3.2mya in human's family tree. what notable environmental change may help explain this?
aridification of east africa, resulting in a shift from woodland to grassland vegetation