THE ICE AGES NSA © Howard Falcon-Lang

CAUSE INTRODUCTION 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.

BUT HOW DID IT HAPPEN? Does anyone know? Can anyone guess?

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 ( )

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. en.wikipedia.org/wiki/Image:Milankovitch_Variations.png

EARTH ORBIT Watch Professor Iain Stewart explain how the earth’s orbit can affect the temperature on the earth Clip 12936

The orbit of the earth around the sun is an oval and not a round shape. Over the years the oval becomes ‘stretched’ due to the pull of the other planets This leads to times when the earth is further from the sun and cooling happens. Usually every 100,000 years. This is a long term cooling and is only noticed over hundreds of years

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 some good ideas

SOLAR VARIATION - Sunspots: an increase in sunspot activity may lead to a very slight increase in the sun’s output and a temporary warming of the earth. Sunspot activity follows 11 and 22 year cycles. The Little Ice Age of may have been linked to periods of very low sunspot activity. Sunspots: an increase in sunspot activity may lead to a very slight increase in the sun’s output and a temporary warming of the earth. Sunspot activity follows 11 and 22 year cycles. The Little Ice Age of may have been linked to periods of very low sunspot activity.

COLOUR OF THE POLES 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. BBC Bitesize - National 5 Geography - The albedo effect 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. Greenhouse gases help to soak up sunlight and keep the Earth warm. Air bubbles in ice cores show that levels fell during Ice Ages so this may have sped up cooling.

VOLCANOES VOLCANIC ERUPTIONS Eruptions of volcanoes can throw millions of tonnes of ash,dust and sulphur dioxide into the atmosphere. This produces aerosols that can reduce the amount of sunlight reaching the earth. This can lead to a temporary cooling of the earth. BBC Bitesize - GCSE Geography - Powerful volcanic eruptions

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 800/le-gulf-stream.jpg

COULD IT REALLY HAPPEN? The Day After Tomorrow? commons.wikimedia.org/wiki/Image:Perito_Moreno_Glacier_Patagonia_Argentina_Luca_Galuzzi_2005.JPG