Today's climate more sensitive to carbon dioxide than in past 12 million years

Jun 06, 2012
Core samples were collected at the sites noted in the North Pacific Ocean. Credit: Jonathan LaRiviere/Ocean Data View

Until now, studies of Earth's climate have documented a strong correlation between global climate and atmospheric carbon dioxide; that is, during warm periods, high concentrations of CO2 persist, while colder times correspond to relatively low levels.

However, in this week's issue of the journal Nature, researchers reveal that about 12-5 million years ago climate was decoupled from atmospheric carbon dioxide concentrations. New evidence of this comes from deep-sea dated to the late of Earth's history.

During that time, temperatures across a broad swath of the North Pacific were 9-14 degrees Fahrenheit warmer than today, while concentrations remained low--near values prior to the Industrial Revolution.

The research shows that, in the last five million years, changes in ocean circulation allowed Earth's climate to become more closely coupled to changes in carbon dioxide concentrations in the atmosphere.

The findings also demonstrate that the climate of modern times more readily responds to changing carbon dioxide levels than it has during the past 12 million years.

"This work represents an important advance in understanding how Earth's past climate may be used to predict future ," says Jamie Allan, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research.

The research team, led by Jonathan LaRiviere and Christina Ravelo of the University of California at Santa Cruz (UCSC), generated the first continuous reconstructions of open-ocean Pacific temperatures during the late .

It was a time of nearly ice-free conditions in the and warmer-than-modern conditions across the continents.

The research relies on evidence of preserved in microscopic plankton skeletons--called microfossils--that long-ago sank to the sea-floor and ultimately were buried beneath it in sediments.

Samples of those sediments were recently brought to the surface in cores drilled into the ocean bottom. The cores were retrieved by marine scientists working aboard the drillship JOIDES Resolution.

The , the scientists discovered, contain clues to a time when the Earth's climate system functioned much differently than it does today.

"It's a surprising finding, given our understanding that climate and carbon dioxide are strongly coupled to each other," LaRiviere says.

"In the late Miocene, there must have been some other way for the world to be warm. One possibility is that large-scale patterns in ocean circulation, determined by the very different shape of the ocean basins at the time, allowed warm temperatures to persist despite low levels of carbon dioxide."

The Pacific Ocean in the late Miocene was very warm, and the thermocline, the boundary that separates warmer surface waters from cooler underlying waters, was much deeper than in the present.

The scientists suggest that this deep thermocline resulted in a distribution of atmospheric water vapor and clouds that could have maintained the warm .

"The results explain the seeming paradox of the warm--but low greenhouse gas--world of the Miocene," says Candace Major, program director in NSF's Division of Ocean Sciences.

Several major differences in the world's waterways could have contributed to the deep thermocline and the warm temperatures of the late Miocene.

For example, the Central American Seaway remained open, the Indonesian Seaway was much wider than it is now, and the Bering Strait was closed.

These differences in the boundaries of the world's largest ocean, the Pacific, would have resulted in very different circulation patterns than those observed today.

By the onset of the Pliocene epoch, about five million years ago, the waterways and continents of the world had shifted into roughly the positions they occupy now.

That also coincides with a drop in average global temperatures, a shoaling of the thermocline, and the appearance of large ice sheets in the Northern Hemisphere--in short, the climate humans have known throughout recorded history.

"This study highlights the importance of in determining climate conditions," says Ravelo. "It tells us that the Earth's climate system has evolved, and that climate sensitivity is possibly at an all-time high."

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NotParker
2.1 / 5 (11) Jun 06, 2012
"that is, during warm periods, high concentrations of CO2 persist, while colder times correspond to relatively low levels."

Actually, during the Eemian CO2 went up after temperature went up and then went down as temperature fell.

And then it was an ice age again.

http://www.ferdin...ian.html
ekim
3.9 / 5 (7) Jun 07, 2012
It appears that the warming occurred over thousands of years during the Eemian. Current warming has occurred over the past century and a half.
Vendicar_Decarian
3.2 / 5 (9) Jun 07, 2012
Global warming preceded by increasing carbon dioxide concentrations during the last deglaciation

Nature 484, 4954 (05 April 2012) doi:10.1038/nature10915

"Actually, during the Eemian CO2 went up after temperature went up and then went down as temperature fell." - ParkerTard

Poor mentally diseased ParkerTard. He will say anything to defend is failed Conservative ideology.
Parsec
4.4 / 5 (7) Jun 07, 2012
@NotParker - do you really think all of the data indicating AGW is real is fabricated? Somehow a global conspiracy to convince everyone to spend money unnecessarily is taking place?

I suspect you understand what it means to cherry-pick data, or to make ad hominiem attacks on the messengers so you don't have to deal with the message they carry. But I have confidence that if you actually studied the data, you would understand the problem.

It's really hard, for example, to say that sea level's aren't really rising when coastlines around the world are undergoing drastic modifications due to that same rising. Its also hard to argue that warming isn't occurring when every instrument used to measure it are in agreement that it is. You can poke holes in the why all you want, but to argue that what is really happening really isn't seems foolish.
Mike_Massen
3.5 / 5 (8) Jun 07, 2012
I'm in Perth, Western Australia.
We had two tornado's overnight causing damage, not as big as those in USA but it is not common at all to get any here before approx the last 20 years.

The average humidity is up.
There is more cold water coming off Antarctica.
The currents off our west coast are changing.

And some people look at anomalies where regions are cooler, obviously sea currents are changing.

If the Atlantic conveyor collapses Europe will have an ice age as a result of global warming. The heat that is no longer being carried north of the equator will build up more around the equatorial regions.

Sea levels are already up by ~20 to 30cm in Tuvali in the last 30 years and rising faster than ever before...

Sure, there are likely to be any number of correlations millennia past for all sorts of reasons. As humans have pumped so much green house gases into the atmosphere new correlations will arise, there is no more any static expectation previous patterns will be repeated...
Vendicar_Decarian
3 / 5 (6) Jun 07, 2012
ParkerTard is a true believer, and undoubtedly a per message employee of some right wing propaganda group.

"@NotParker - do you really think all of the data indicating AGW is real is fabricated?" - Parsec

I've seen his kind before.
Birger
4.2 / 5 (5) Jun 07, 2012
True believers will not have their faith shaken by mere facts.
And politicians pander to those True Believers if they see an avantage in it.
Alas, in some political circels, expressing concern about climate is enough to be labelled "Not one of us".
So we stumble on towards the edge of the cliff...
dogbert
1.7 / 5 (7) Jun 07, 2012
Noting that CO2 levels and climate do not track together as is noted in this article would tend to show that AGW due to CO2 was a wrong conclusion.

The article concludes instead that "climate sensitivity is possibly at an all-time high."

Data does not matter when the conclusion is predetermined by political agenda.
rubberman
4.3 / 5 (6) Jun 07, 2012
Noting that CO2 levels and climate do not track together as is noted in this article would tend to show that AGW due to CO2 was a wrong conclusion.

The article concludes instead that "climate sensitivity is possibly at an all-time high."

Data does not matter when the conclusion is predetermined by political agenda.


"The research shows that, in the last five million years, changes in ocean circulation allowed Earth's climate to become more closely coupled to changes in carbon dioxide concentrations in the atmosphere." - from the article

If the research doesn't show it, they can't say that the research shows it....try again.
Sigh
4 / 5 (4) Jun 07, 2012
Noting that CO2 levels and climate do not track together as is noted in this article would tend to show that AGW due to CO2 was a wrong conclusion.

Not necessarily. Another conclusion consistent with this study is that there is more than one way to get warming.

You might die from old age, you might die in a car accident. If I find you died young, I have not shown that you can't die from old age.
barakn
3.7 / 5 (3) Jun 07, 2012
Noting that CO2 levels and climate do not track together as is noted in this article would tend to show that AGW due to CO2 was a wrong conclusion.

No. It shows that in the past, a natural trigger such as a change in the Earth's tilt could cause a minor warming, releasing enough CO2 to accelerate and magnify that initial warming.
NotParker
1.5 / 5 (8) Jun 07, 2012
Noting that CO2 levels and climate do not track together as is noted in this article would tend to show that AGW due to CO2 was a wrong conclusion.

No. It shows that in the past, a natural trigger such as a change in the Earth's tilt could cause a minor warming, releasing enough CO2 to accelerate and magnify that initial warming.


And then the tilt changes again, the temperature goes down, and the ice age returns. Warming causes CO2, not CO2 causes warming. The post-LIA warming caused CO2 to go up.

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