Has the puzzle of rapid climate change in the last ice age been solved?

Aug 19, 2014
Figure A: The Northern Hemisphere in a cold (stadial) phase During the cold stadial periods of the last ice age, massive ice sheets covered northern parts of North America and Europe. Strong northwest winds drove the Arctic sea ice southward, even as far as the French coast. Since the extended ice cover over the North Atlantic prevented the exchange of heat between the atmosphere and the ocean, the strong driving forces for the ocean currents that prevail today were lacking. Ocean circulation, which is a powerful “conveyor belt” in the world’s oceans, was thus much weaker than at present, and consequently transported less heat to northern regions. Map: Alfred-Wegener-Institut Figure A: The Northern Hemisphere in a cold (stadial) phase

Over the past one hundred thousand years cold temperatures largely prevailed over the planet in what is known as the last ice age. However, the cold period was repeatedly interrupted by much warmer climate conditions. Scientists have long attempted to find out why these drastic temperature jumps of up to ten degrees took place in the far northern latitudes within just a few decades. Now, for the first time, a group of researchers at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have been able to reconstruct these climate changes during the last ice age using a series of model simulations. The surprising finding is that minor variations in the ice sheet size can be sufficient to trigger abrupt climate changes. The new study was published online in the scientific journal Nature last week and will be appearing in the 21 August print issue.

During the last ice age a large part of North America was covered with a massive ice sheet up to 3km thick. The water stored in this is part of the reason why the was then about 120 meters lower than today. Young Chinese scientist Xu Zhang, lead author of the study who undertook his PhD at the Alfred Wegener Institute, explains. "The rapid changes known in the scientific world as Dansgaard-Oeschger events were limited to a period of time from 110,000 to 23,000 years before present. The did not take place at the extreme low sea levels, corresponding to the time of maximum glaciation 20,000 years ago, nor at high sea levels such as those prevailing today - they occurred during periods of intermediate ice volume and intermediate sea levels." The results presented by the AWI researchers can explain the history of climate changes during glacial periods, comparing simulated model data with that retrieved from ice cores and marine sediments.

During the cold stadial periods of the last ice age, massive ice sheets covered northern parts of North America and Europe. Strong westerly winds drove the Arctic sea ice southward, even as far as the French coast. Since the extended ice cover over the North Atlantic prevented the exchange of heat between the atmosphere and the ocean, the strong driving forces for the ocean currents that prevail today were lacking. Ocean circulation, which is a powerful "conveyor belt" in the world's oceans, was thus much weaker than at present, and consequently transported less heat to northern regions.

Figure B: The Northern Hemisphere in a warm phase (a brief, warm interstadial phase during glacial climates) During the extended cold phases the ice sheets continued to thicken. When higher ice sheets prevailed over North America, typical in periods of intermediate sea levels, the prevailing northwest winds split into two branches. The major wind field ran to the north of the so-called Laurentide Ice Sheet and ensured that the sea ice boundary off the European coast shifted to the north. Ice-free seas permit heat exchange to take place between the atmosphere and the ocean. At the same time, the southern branch of the northwesterly winds drove warmer water into the ice-free areas of the northeast Atlantic and thus amplified the transportation of heat to the north. The modified conditions stimulated enhanced circulation in the ocean. Consequently, a thicker Laurentide Ice Sheet over North America resulted in increased ocean circulation and therefore greater transportation of heat to the north. The climate in the Northern Hemisphere became dramatically warmer within a few decades until, due to the retreat of the glaciers over North America and the renewed change in wind conditions, it began to cool off again. Map: Alfred-Wegener-Institut

During the extended cold phases the ice sheets continued to thicken. When higher ice sheets prevailed over North America, typical in periods of intermediate sea levels, the prevailing westerly winds split into two branches. The major wind field ran to the north of the so-called Laurentide Ice Sheet and ensured that the sea ice boundary off the European coast shifted to the north. Ice-free seas permit heat exchange to take place between the atmosphere and the ocean. At the same time, the southern branch of the northwesterly winds drove warmer water into the ice-free areas of the northeast Atlantic and thus amplified the transportation of heat to the north. The modified conditions stimulated enhanced circulation in the ocean. Consequently, a thicker Laurentide Ice Sheet over North America resulted in increased ocean circulation and therefore greater transportation of heat to the north. The climate in the Northern Hemisphere became dramatically warmer within a few decades until, due to the retreat of the glaciers over North America and the renewed change in wind conditions, it began to cool off again.

"Using the simulations performed with our climate model, we were able to demonstrate that the climate system can respond to small changes with abrupt climate swings," explains Professor Gerrit Lohmann, leader of the Paleoclimate Dynamics group at the Alfred Wegener Institute, Germany. In doing so he illustrates the new study's significance with regards to contemporary . "At medium sea levels, powerful forces, such as the dramatic acceleration of polar ice cap melting, are not necessary to result in abrupt climate shifts and associated drastic temperature changes."

At present, the extent of Arctic sea ice is far less than during the last glacial period. The Laurentide Ice Sheet, the major driving force for ocean circulation during the glacials, has also disappeared. Climate changes following the pattern of the last age are therefore not to be anticipated under today's conditions.

Figure C: Schematic depiction of current climate conditions in the Northern Hemisphere At present, the extent of the Arctic sea ice is far less than during the last glacial period. The Laurentide Ice Sheet, the major driving force for ocean circulation during the glacials, has also disappeared. Model simulations demonstrate that today’s climate is much more robust in resisting the changes which existed during phases of intermediate ice thickness and intermediate sea levels. It was then, during the last ice age, that the most rapid temperature swings in the Northern Hemisphere took place. Map: Alfred-Wegener-Institut

"There are apparently some situations in which the climate system is more resistant to change while in others the system tends toward strong fluctuations," summarises Gerrit Lohmann. "In terms of the Earth's history, we are currently in one of the climate system's more stable phases. The preconditions, which gave rise to rapid temperature changes during the last do not exist today. But this does not mean that sudden climate changes can be excluded in the future."

Explore further: Large sea ice changes North of Swalbard

More information: Xu Zhang, Gerrit Lohmann, Gregor Knorr, Conor Purcell: Abrupt glacial climate shifts controlled by ice sheet changes. Nature, DOI: 10.1038/nature13592

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User comments : 11

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Science Officer
1 / 5 (6) Aug 19, 2014
We're actually still in an Ice Age, which has lasted for about 2.6 million years. Enjoy the current inter glacial warming period while you can, it's the exception, rather than the norm. Compared to massive ice sheets covering the continents, the current climate is just fine. In fact, if we can warm things up a little bit more, maybe we can postpone the next Big Chill for awhile.
Scroofinator
5 / 5 (2) Aug 19, 2014
We're actually still in an Ice Age, which has lasted for about 2.6 million years.

Do you have a link supporting this? I would be interested to see this explanation.
Vietvet
3.7 / 5 (3) Aug 19, 2014
We're actually still in an Ice Age, which has lasted for about 2.6 million years.

Do you have a link supporting this? I would be interested to see this explanation.


He can't provide any peer reviewed studies supporting his POV. I'm sure there are plenty of denialist blogs he could link to, but I think that's what you want to find.
Scroofinator
1 / 5 (2) Aug 19, 2014
I don't care what the source is, as long as it's remotely scientific and corroborating I'll read it. You see, I judge science based on content, not by who writes it.
Vietvet
3.7 / 5 (3) Aug 19, 2014
@Scroofinator.

"remotely scientific"?

The only place that exists is on pseudoscience sites meant for the gullible and run by charlatans.
antigoracle
1 / 5 (3) Aug 19, 2014
Do you have a link supporting this? I would be interested to see this explanation.

I know it's tough for you in the AGW Cult's peanut gallery, you know having to share a lone neuron and all. So, let me google that for you...mkay.

https://www.googl...fW0YHQCQ
Scroofinator
1 / 5 (3) Aug 19, 2014
Vietvet, what makes you think you get to judge what other people want to consider as science? It's surely not your 'veteran' status. I highly doubt you actually are, I bet you get paid by the same guy as Stumpy. Two convenient excuses for why you two are constantly posting the same BS all the time. A couple of old retired guys who claim to be scientific but rarely offer anything to science. The only thing your kind does is stagnate true scientific progress, all for a dime.
Vietvet
3.7 / 5 (3) Aug 19, 2014
Do you have a link supporting this? I would be interested to see this explanation.

I know it's tough for you in the AGW Cult's peanut gallery, you know having to share a lone neuron and all. So, let me google that for you...mkay.

https://www.googl...fW0YHQCQ


http://www.smiths.../?no-ist
Scroofinator
not rated yet Aug 19, 2014
anti-gore-butthole

you must not pay attention too often, I'm def not in the "AGW Cult's peanut gallery". Really don't know where you could get that.

I was asking for a specific source backing his/her specific claim. Something that he/she should readily be able to supply.
Vietvet
4 / 5 (4) Aug 19, 2014
Vietvet, what makes you think you get to judge what other people want to consider as science?


Do you want to reconsider that statement? Think about it.

There is a huge difference between science and pseudoscience and when I read a comment spouting unscientific garbage I'm going to call them on it.
Vietvet
4 / 5 (4) Aug 20, 2014
I bet you get paid by the same guy as Stumpy.


If only that were true. I can always use some extra cash for my book buying addiction.

I am retired but I'm considerably older than Captain Stumpy while he is the superior writer.

You can believe what you want about me but the importance of speaking the truth to power I learned in the Marine Corps. Telling a superior officer, when asked, what they didn't want to hear was expected and respected. That integrity was ingrained in me and carried over into my career as a construction superintendent.

When I smell bullshit I'm not going to call it perfume.

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