Periodic Ice AgesPeriodic Ice Ages

• When the Last Ice Age was at its maximum, ice sheets covered much of Europe and North America. So what caused it?

NASA

Many Ice AgesMany Ice Ages

© Ian and Tanya West

• By studying the layers of gravel left behind by the ice, geologists figured out that there hadn’t been just one Great Ice Age.

Ice age layers

• Rather, over the last two and a half million years, there had been many ice ages each separated by a short warmer period.

Orbital wobblesOrbital wobblesen.wikipedia.org/wiki/Milutin_Milanković commons.wikimedia.org/wiki/Image:Milankovitch-cycles_hg.png

• In the 1940s, Milanković wondered whether wobbles in the Earth’s orbit around the Sun could explain multiple Ice Ages by changing the amount of heating reaching the Earth

Milutin Milanković (1879-1958)

Oribital Irradiance CyclesOribital Irradiance Cycles

• Milanković added up all the orbital wobbles and predicted that ice ages should occur in regular cycles - probably happening every hundred thousand years or so.

The Big QuestionThe Big Question

• But one big question remained: Exactly how did changes in the amount of solar energy reaching the Earth trigger Ice Age cycles?

• So far there are no firm answers but three good ideas

Reflectivity of the Poles –Runaway Reflectivity of the Poles –Runaway Effect?Effect?

• The first idea is that as the Earth cooled, green forests in the far north were replaced by white ice.

• Ice reflects back more of the sun’s energy, so this would have caused further cooling, leading to an Ice Age.

Absorbs energy: Warming

Reflects energy: Coolingen.wikipedia.org/wiki/Image:AntarcticaDomeCSnow.jpg

Greenhouse Gases Greenhouse Gases

© NOAA

Greenhouse Gas levels dropped during Ice Ages

Last Ice Age =Low Greenhouse Gas

• The second idea is that changes in greenhouse gas levels were to blame.

• Air bubbles in ice cores show that levels fell during Ice Ages so this may have sped up cooling.

Mechanism for change is Not well understood

Ocean CurrentsOcean Currents

Gulf Stream warms the Arctic

• The third idea is that ocean currents like the Gulf Stream were important.

• This current helps warm up the Arctic. If it switched off this would cool the Arctic further and increase the likelihood of an Ice Age

Again, “switch-off mechanismNot understood

www.sott.net/image/image/tmp/1168547904.692692.7800/le-gulf-stream.jpg

How to Prevent Next One?How to Prevent Next One?

If long term climatology holds – we can If long term climatology holds – we can expect another mini ice age to start in about expect another mini ice age to start in about 10,000 years10,000 years

This would: a) reduce the availibility of fresh This would: a) reduce the availibility of fresh water and b) reduce the available land mass water and b) reduce the available land mass for habitationfor habitation

Would likely be a very large problem, if Would likely be a very large problem, if humanity is still here in 10,000 years.humanity is still here in 10,000 years.

Ice Age Europe: CoastsIce Age Europe: Coastswww.uwgb.edu/dutchs/EarthSC202Notes/GLACgeog.HTM

Ice sheet

Tundra

• With so much water locked up as ice, sea level was much lower in the Last Ice Age and Britain was attached to mainland Europe.

• This allowed humans, animals and plants to migrate far and wide.

Ice Age Europe GeographyIce Age Europe Geography20,000 years ago

www.geocities.com/reginheim/europeiceage.gif

• Europe was very different at the height of the Last Ice Age.

Thick ice sheets in north

Frozen tundra in centre

Conifer forests in south

• We will focus on the tundra region of southern England.

Pacific NW EffectsPacific NW Effects

Eventually Glacial Lake Missoula Eventually Glacial Lake Missoula Was Formed from Melting IceWas Formed from Melting Ice

Lake contained about 500 cubic miles of Lake contained about 500 cubic miles of water.water.

Etched Wave ShelvesEtched Wave Shelves

PNW Analog – The Bretz FloodsPNW Analog – The Bretz Floods

Ice Dam on Glacial Lake Missoula breaks Ice Dam on Glacial Lake Missoula breaks suddenlysuddenly

Catastrophe and CultureCatastrophe and Culture The Bretz/Missoula Flood(s) was another The Bretz/Missoula Flood(s) was another

post Ice Age deluge that would have post Ice Age deluge that would have catastrophically dispersed any native catastrophically dispersed any native population in random directions.population in random directions.