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Climate Change: Paleoclimate
and the Oceanic Perspective
Some of chapters 19, 20 & 21
Pete Kozich
Climate Change Factors
• Extraterrestrial factors:
Solar output, Earth-Sun geometry,
Interstellar dust… focus on these first
• Intra-Earth System factors:
Atmospheric reflectivity (aerosols, clouds, and
precipitation) Surface reflectivity, Continental
drift, Atmospheric chemistry, Volcanic
emissions, Atmosphere-Ocean heat
exchange, Mountain building
Climate Change
Extraterrestrial factors
• Changes in solar output
Sun getting more luminous over LONG periods
• Changes in Earth-Sun geometry
Eccentricity (100 ky), Precession (26 kyr),
Obliquity (41 ky)
• Changes in interstellar dust
• Violent events
Meteoritic impacts, supernovae, gamma ray
bursts
Climate Change
• Changes in Earth-Sun geometry
• Eccentricity
Earth’s orbit nearly circular now (3% difference
between perihelion and aphelion, becoming more
circular). Cooler summers. Maximum difference of 9%.
• Precession
Wobbling of axis. North Pole currently points toward
sun at aphelion (cooler summers currently).
• Obliquity
Tilt of axis varies between 22.5 deg and 24.5 deg.
Currently in the middle. Less tilt, cooler summers.
Weaker effect than other two.
Climate Change
• Violent events
• Comet and/or asteroid impacts eject much dust
and aerosols into the atmosphere, which reflect
incoming sunlight.
--Global cooling and glaciation result.
At least partially responsible for Cretaceous mass
extinction.
• Gamma ray bursts believed to also result in global
cooling.
• Nearby supernovae explosions would also be
traumatic.
Climate change
• Intra-Earth System factors:
Atmospheric reflectivity (aerosols, clouds, and
precipitation) Surface reflectivity, Continental
drift, Atmospheric chemistry, Volcanic
emissions, Atmosphere-Ocean heat
exchange, Mountain building
Climate Change
• Continental drift. Land gains/loses energy more
quickly than water. Placement of continents
important for temperature. Increased polar ice
lowers sea level but also depresses land
underneath ice (latter is a lesser effect, though).
Rapidly expanding mid-ocean ridges displace
water onto continents.
• Volcanic emissions. Increased sulfur dioxide into
stratosphere reduces incoming solar radiation.
• Mountain building. Land pushed higher up will
be cooler. Precipitation and cloud changes also.
Climate Change
• Atmospheric-Oceanic Heat Exchange.
Oceans interact with air and land.
Evaporation, precipitation, runoff, glaciation
are common processes. Seas, air, and land
also exchange gases, and solid and liquid
compounds and affect heating and
distribution of heat on Earth.
Less air-sea interaction would most likely lead
to less transport and colder poles.
Climate
• Oceans generally tend to moderate climate.
Water has a higher heat capacity than land,
and latent heat release from water in clouds
and precipitation also moderates
temperatures over the Earth’s surface.
• Two concrete examples of the oceans
distributing heat with global implications
include the Thermohaline Circulation (THC)
and El Nino-Southern Oscillation (ENSO).
Thermohaline Circulation
• Salty, cold (dense) water near Iceland sinks
and is distributed throughout the oceans
• It slowly rises in the Pacific, especially the
northern Pacific, where overlying waters are
not warmer or less dense
• It returns to the North Atlantic, where it is
finally cool again, acquires more salinity and
sinks again
THC
• Generally speaking, glaciation removes water but
retains salt near the ocean surface.
• Salty water is denser and sinks from the surface
to the ocean bottom. This newly formed deep
water was in contact with the Earth’s atmosphere
and so contains oxygen.
• THC generally stronger during strong periods of
glaciation, though increased heat transport to
high latitudes will cap the THC strength.
• Little glaciation. Water not salty enough to sink.
The ocean stagnates.
THC
• Without heat transport via the THC, heat builds
up in the equator, and cools at the poles. This
will tend to try to get the THC going again, as
glaciation would promote THC development.
• Most of the Earth’s past 500 million years
occurred without glaciation. THC role not well
understood in past climates. THC did not
function as today in the mid-Cretaceous, when
deep oceans were anoxic.
THC
• At the moment, the THC appears to be
slowing down, due to lesser salinity in the
North Atlantic from increased melting of polar
sea ice.
• The Gulf Stream has shifted further south,
with less warm water being transported from
the equator to the poles. This may end up
cooling off the poles and could cool the Earth
or lessen the effects of global warming.
• Not sure what will happen in the future.
El Nino – Southern Oscillation
• In the deep tropics, surface winds blow from east
to west, and are reversed about 10 miles up
• In the Pacific, this effect can vary greatly.
Normally, easterly winds prevail and upwell
cooler water off of the west coast of South
America.
• During an El Nino, the trade winds weaken and
less cool water is pulled up off the South
American coast.
ENSO
• La Ninas feature even cooler than normal
water off of South America and the nearby
Pacific.
• Changes in deep clouds in the deep tropics
can alter midlatitude and polar weather.
• Overall, globe is slightly warmer during El Nino
events than La Nina events.
• Possibly correlated with global warming.
ENSO frequency does appear to show
multidecadal cycles.
Climate Change
• Future climatic shifts may be accompanied by
changes in the THC and ENSO
• Both THC and ENSO have oceanic-atmospheric
interactions and affect global heat transport
and global temperatures.
• Both alter climate and are altered by the
climate (two-way feedback between THC and
climate and between ENSO and climate).
Paleoclimate
• We can estimate climate change from the
fossil record.
• Sun emitting 5% more energy per billion years
now, but a lot of variability within it, with one
smaller scale variability about 120 – 160 my.
• Oxygen levels not high until less than 600 my.
Carbon dioxide levels fell early-mid Paleozoic
Era due to increasing photosynthetic activity.
Temperature and carbon dioxide graphs not
always match up with same trends.
Paleoclimate
Devonian
oxygen
increasing
Paleoclimate
Cretaceous
cooling
Devonian
cooling
Ordovician
glaciation
Paleoclimate
Cretaceous sea
level drop
Paleoclimate
Paleoclimate
End Cretaceous low carbon dioxide
Devonian carbon dioxide drawdown
Summary
• Most convincing evidence for glaciation at end
of Ordovician, cooling in late Devonian (effects
of plants?), and cooling during late Cretaceous
(asteroid and/or volcanism?)
• Perhaps a cooling event at end of Triassic
• End of Permian and Cambrian periods
inconsistent and currently used climate
change indicators have not provided us with a
definite picture of climate change then.