Climate Change: Paleoclimate and the Oceanic Perspective

Some of chapters 19, 20 & 21Pete 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

PaleoclimateOrdovician glaciationDevonian

coolingCretaceous cooling

Paleoclimate

PaleoclimateCretaceous sea level drop

Paleoclimate

Devonian carbon dioxide drawdownEnd Cretaceous low carbon dioxide

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.