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thisweekinscience:

New and exciting discoveries in the earth’s past ice age

DURING the summer of 2008, workers excavating Ground Zero in Lower Manhattan dug right down to the bedrock. There, they found something unexpected: a huge pothole more than 10 metres deep, the crevices around it crammed with stones of several different kinds of rock. The consulting geologist immediately recognised these features. The stones had been carried there from many miles away by a glacier that had ground across the bedrock. At some point, a swirling torrent of glacial meltwater had carved out the pothole.

From potholes in New York City to forests beneath the sea, evidence of the time ice dominated the world is all around us. The last great ice age began around 120,000 years ago. One massive ice sheet, more than 3 kilometres thick in places, grew in fits and starts until it covered almost all of Canada and stretched down as far as Manhattan. Another spread across most of Siberia, northern Europe and Britain, stopping just short of what is now London. Elsewhere many smaller ice sheets and glaciers grew, vast areas turned into tundra and deserts expanded as the planet became drier.

With so much ice on land, sea level was 120 metres lower than it is today. Britain and Ireland were part of mainland Europe. Florida was twice the size it is now, with Tampa stranded far from the coast. Australia, Tasmania and New Guinea were all part of a single land mass called Sahul. The planet was barely recognisable.

Then, 20,000 years ago, a great thaw began. Over the following 10,000 years, the average global temperature rose by 3.5 °C and most of the ice melted. Rising seas swallowed up low-lying areas such as the English Channel and North Sea, forcing our ancestors to abandon many settlements. So what drove this dramatic transformation of the planet? Continue reading 

scinerds:

Volcanoes and the Little Ice Age: Not the Smoking Gun?
By Erik Klemetti

There is the tendency in our fast-paced world for lots and lots of articles to get written about science before anyone beyond the researchers and the reviewers actually sees the science. This is mostly thanks to the fact that press releases come out before the actual study – and who has time to read a study when there is a handy press release with all the bits? Yesterday saw an example of just this – a whole lot of “news” without a lot of assessment of the study itself.

The paper itself is called “Abrupt Onset of the Little Ice Age triggered by volcanism and sustained by sea-ice/ocean feedbacks” by Gifford Miller and a host of coauthors (mostly climatologists) in the Geophysical Research Letters. After seeing a post about it on Dot Earth, I knew that the media would eat this up and wouldn’t you know it, within hours there were dozens of articles mostly telling us what the initial press release already said … and not much else. It took a while for the PDF of the article to appear on the GRL website, but after it did, I sat down with it to see what the “smoking guns” were that they identified.

I’m not going to discuss the climate models or interpretation – more or less, they sampled moss and lake sediment in Canada and Iceland to constrain the dates of the onset of the Little Ice Age. Then, they used climate models and data about volcanic atmospheric sulfur (from Gao et al., 2008, more on this paper in a bit) to model how the atmosphere and oceans would respond and if it correlated with their ages. The long and short is they found that a large sulfur loading in the atmosphere could trigger increased sea ice that would prompt cooler global climate, thus the Little Ice Age.

Continue reading over at Wired.