Periodic 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 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 wobbles Orbital wobbles en.wikipedia.org/wiki/Milutin_Milankovićcommons.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 ( )

Oribital 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 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 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: Cooling en.wikipedia.org/wiki/Image:AntarcticaDomeCSnow.jpg

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 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 mechanism Not understood 800/le-gulf-stream.jpg

How to Prevent Next One?  If long term climatology holds – we can expect another mini ice age to start in about 10,000 years  This would: a) reduce the availibility of fresh water and b) reduce the available land mass for habitation  Would likely be a very large problem, if humanity is still here in 10,000 years.

Ice Age Europe: Coasts 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 Geography 20,000 years ago 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 Effects

Eventually Glacial Lake Missoula Was Formed from Melting Ice Lake contained about 500 cubic miles of water.

Etched Wave Shelves

PNW Analog – The Bretz Floods  Ice Dam on Glacial Lake Missoula breaks suddenly

Catastrophe and Culture  The Bretz/Missoula Flood(s) was another post Ice Age deluge that would have catastrophically dispersed any native population in random directions.