Climate Debate Over: Last Ice Age Ended By Rise in CO2 Levels

[Obama 2012 1,714]

Yup, no way in hell this was possible. The last Ice Age could not have ended without big rigs, lawn mowers, and cow farts! We are so effing doomed!

We've got to stop the CO2 people!!! We are preventing an Ice Age here! Can't you see how terrible this is?!?!?!?!?!

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http://www.bbc.co.uk/news/science-environment-17611404

A new, detailed record of past climate change provides compelling evidence that the last ice age was ended by a rise in temperature driven by an increase in atmospheric carbon dioxide.

The finding is based on a very broad range of data, including even the shells of ancient tiny ocean animals.

A paper describing the research appears in this week's edition of Nature.

The team behind the study says its work further strengthens ideas about global warming.

"At the end of the last ice age, CO2 rose from about 180 parts per million (ppm) in the atmosphere to about 260; and today we're at 392," explained lead author Dr Jeremy Shakun.

"So, in the last 100 years we've gone up about 100 ppm - about the same as at the end of the last ice age, which I think puts it into perspective because it's not a small amount. Rising CO2 at the end of the ice age had a huge effect on global climate."

The study covers the period in Earth history from roughly 20,000 to 10,000 years ago.

This was the time when the planet was emerging from its last deep chill, when the great ice sheets known to cover parts of the Northern Hemisphere were in retreat.

The key result from the new study is that it shows the carbon dioxide rise during this major transition ran slightly ahead of increases in global temperature.

This runs contrary to the record obtained solely from the analysis of Antarctic ice cores which had indicated the opposite - that temperature elevation in the southern polar region actually preceded (or at least ran concurrent to) the climb in CO2.

This observation has frequently been used by some people who are sceptical of global warming to challenge its scientific underpinnings; to claim that the warming link between the atmospheric gas and global temperature is grossly overstated.

But Dr Shakun and colleagues argue that the Antarctic temperature record is just that - a record of what was happening only on the White Continent.

By contrast, their new climate history encompasses data from all around the world to provide a much fuller picture of what was happening on a global scale.

This data incorporates additional information contained in ices drilled from Greenland, and in sediments drilled from the ocean floor and from continental lakes.

These provide a range of indicators. Air bubbles trapped in ice, for example, will record the past CO2 concentrations in the atmosphere. Past temperatures can also be inferred from ancient planktonic marine organisms buried in the sediments. That is because the amount of magnesium they would include in their calcite skeletons and shells was dependent on the warmth of the water in which they swam.

"Our global temperature looks a lot like the pattern of rising CO2 at the end of the ice age, but the interesting part in particular is that unlike with these Antarctic ice core records, the temperature lags a bit behind the CO2," said Dr Shakun, who conducted much of the research at Oregon State University but who is now affiliated to Harvard and Columbia universities.

"You put these two points together - the correlation of global temperature and CO2, and the fact that temperature lags behind the CO2 - and it really leaves you thinking that CO2 was the big driver of global warming at the end of the ice age," he told BBC News.

Dr Shakun's team has now constructed a narrative to explain both what was happening on Antarctica and what was happening globally:

This starts with a subtle change in the Earth's orbit around the Sun known as a Milankovitch "wobble", which increases the amount of light reaching northern latitudes and triggers the collapse of the hemisphere's great ice sheets

This in turn produces vast amounts of fresh water that enter the North Atlantic to upset ocean circulation

Heat at the equator that would normally be distributed northwards then backs up, raising temperatures in the Southern Hemisphere

This initiates further changes to atmospheric and ocean circulation, resulting in the Southern Ocean releasing CO2 from its waters

The rise in CO2 sets in train a global rise in temperature that pulls the whole Earth out of its glaciated state

Prof Eric Wolff from the British Antarctic Survey was the chief scientist on the longest Antarctic ice core, which was drilled at Dome Concordia in 2001/2002. This core records eight ice ages, not just the most recent, stretching back some 800,000 years.

He was not involved in the Nature study. Prof Wolff told this week's Science In Action programme on the BBC World Service:

"It looks as though whatever kicked off this whole sequence of events to get out of the ice age was something really, in global terms, rather minor and regional, and yet it led to a sequence of events that led to a complete change in the way the surface of the Earth looked, with ice sheets disappearing.

"So, that just reminds us that although climate might seem quite steady to us because it's been relatively steady for the last few thousand years, it is actually capable of undergoing big changes. And as one famous palaeoclimatologist put it: 'we poke it at our peril'."

[Obama 2012 1,714]

Shake It Off: Earth's Wobble May Have Ended Ice Age

http://www.nhpr.org/post/shake-it-earths-wobble-may-have-ended-ice-age

The last big ice age ended about 11,000 years ago, and not a moment too soon — it made a lot more of the world livable, at least for humans.

But exactly what caused the big thaw isn't clear, and new research suggests that a wobble in the Earth kicked off a complicated process that changed the whole planet.

Ice tells the history of the Earth's climate: Air bubbles in ice reveal what the atmosphere was like and what the temperature was. And scientists can read this ice, even if it's been buried for thousands of years.

But when it comes to the last ice age, ice has a mixed message.

The conventional wisdom is that carbon dioxide increased in the atmosphere starting about 19,000 years ago. Then the ice melted. The logical conclusion? The greenhouse effect.

But the Antarctic was getting warmer even before CO2 levels went up. So which came first in the Antarctic, warming or CO2?

"The problem is, [the Antarctic is] just one spot on the map, and it's a dicey way to slice up global climate change by looking at one point," says Jeremy Shakun, a climate scientist at Harvard University. So he went way beyond the Antarctic — he collected samples of ice, rock and other geologic records from 80 places around the world and found that CO2 levels did, in fact, precede global warming.

Here's his scenario for what killed the ice age, which was published in the journal Nature this week.

About 20,000 years ago, the Earth — the whole planet — wobbled on its axis. That happens periodically. But this time, a lot more summer sunlight hit the northern hemisphere. Gigantic ice sheets in the Arctic and Greenland melted.

"That water is going to go into the North Atlantic, and that happens to be the critical spot for this global conveyer belt of ocean circulation," Shakun says.

The conveyer belt is how scientists describe the huge, underwater loop-the-loop that water does in the Atlantic: Cold Arctic water sinks and moves south while warm water in the southern Atlantic moves north.

The trouble is that the sudden burst of fresh meltwater didn't sink, so the conveyer belt stopped.

"It's like, you know, sticking a fork in the conveyer belt at the grocery store," Shakun says. "The thing just jams up; it can't keep sinking, and the whole thing jams up."

So warm water in the south Atlantic stayed put. That made the Antarctic warmer. Eventually, ocean currents and wind patterns changed, and carbon dioxide rose up out of the southern oceans and into the atmosphere.

Eric Wolff, a climate scientist at the British Antarctic Survey, isn't convinced a wobble was the trigger — the planet had wobbled before and not melted the ice. But he says whatever did start the process during the ice age, the subsequent increase in CO2 created a runaway greenhouse effect worldwide.

"The CO2 increase turned what initially was a Southern Hemisphere warming into a global warming. That's a very nice sequence of events to explain what happened between about 19,000 and 11,000 years ago," Wolff says.

But that's a process that has taken about 8,000 years. And Shakun's research found that the amount of CO2 it took to end the ice age is about the same amount as humans have added to the atmosphere in the past century.