Reliability of Greenland ice cores questioned for Younger Dryas only

29 Jun
It seems now that the main proxy to understand Northern Hemisphere glaciation, the Greenland ice cores, is not as straightforward as scientists used to think. At least that is what a new study claims in relation to the Younger Dryas (only):
Zhengyu Liu, Younger Dryas cooling and the Greenland climate response to CO2. PNAS 2012. Pay per view (6-month embargo or depending on world region).


Greenland ice-core δ18O-temperature reconstructions suggest a dramatic cooling during the Younger Dryas (YD; 12.9–11.7 ka), with temperatures being as cold as the earlier Oldest Dryas (OD; 18.0–14.6 ka) despite an approximately 50 ppm rise in atmospheric CO2. Such YD cooling implies a muted Greenland climate response to atmospheric CO2, contrary to physical predictions of an enhanced high-latitude response to future increases in CO2. Here we show that North Atlantic sea surface temperature reconstructions as well as transient climate model simulations suggest that the YD over Greenland should be substantially warmer than the OD by approximately 5 °C in response to increased atmospheric CO2. Additional experiments with an isotope-enabled model suggest that the apparent YD temperature reconstruction derived from the ice-core δ18O record is likely an artifact of an altered temperature-δ18O relationship due to changing deglacial atmospheric circulation. Our results thus suggest that Greenland climate was warmer during the YD relative to the OD in response to rising atmospheric CO2, consistent with sea surface temperature reconstructions and physical predictions, and has a sensitivity approximately twice that found in climate models for current climate due to an enhanced albedo feedback during the last deglaciation.

The problem is that, when compared with other records, the Greenland Ice cores’ oxygen isotope ration does not hold. The explanation is complex and related to CO2 levels, the North American Ice Sheet (which was already in retreat) and the different composition of oxygen isotopes when they arrived from the Pacific Ocean.

From the Archaeology News Network:

Working with UW-Madison climatologist Zhengyu Liu, collaborators at the National Center for Atmospheric Research and others, Carlson found their computer climate model breaking down on the Younger Dryas.
While it could reliably recreate temperatures in the Oldest Dryas — a similar cooling period about 18,000 years ago — they just couldn’t find a lever in the model that would simulate a Younger Dryas that matched the Greenland ice cores.
“You can totally turn off ocean circulation, have Arctic sea ice advance all the way across the North Atlantic, and you still will have a warmer climate during the Younger Dryas than the Oldest Dryas because of the carbon dioxide,” Carlson says.
By the time the Younger Dryas rolled around, there was more carbon dioxide in the air — about 50 parts per million more. The warming effects of that much CO2 overwhelmed the rest of the conditions that make the Oldest and Younger Dryas so alike, and demonstrates a heightened sensitivity for Arctic temperatures to rising greenhouse gases in the atmosphere.
The researchers zeroed in on the Northern Hemisphere’s temperature outlier, Greenland ice cores, and found that the conversion of oxygen isotope ratio to temperature typically used on the ice cores did not account for the sort of crash climate change occurring during the Younger Dryas. It assumes prevailing winds and jet streams and storm tracks are providing the moisture for Greenland precipitation from the Atlantic Ocean.

“The Laurentide ice sheet, which covered much of North America down into the northern United States, is getting smaller as the Younger Dryas approaches,” Carlson says. “That’s like taking out a mountain of ice three kilometers high. As that melts, it allows more Pacific Ocean moisture to cross the continent and hit the Greenland ice sheet.” The two oceans have distinctly different ratios of oxygen isotopes, allowing for a different isotope ratio where the water falls as snow.

Hat tip: Pileta.

Some temperature proxies for the Younger Dryas

12 responses to “Reliability of Greenland ice cores questioned for Younger Dryas only

  1. Caz

    July 5, 2012 at 2:01 am

    Another piece of evidence highlighting the flaws of the CO2-drives-climate hypothesis.

  2. Maju

    July 5, 2012 at 2:40 am

    It has nothing to do with your nonsense. If you don't believe in modern climate warning, just look at photos of the Kilimanjaro (or any other glacier on Earth): it's warming and fast. This only highlights that there are some hidden complexities but not at all what you wish to imagine: we are walking the path of human self-caused extinction and denial is of no help at all.

  3. Caz

    July 5, 2012 at 3:10 am

    You are a scientist. I recommend you read up on climate science. You will discover all this alarm is nonsense. I suggest you start by reading how Steve McIntyre discovered Michael Mann's infamous hockey stick graph is statistically unsound. Then please read about the many warm periods during the holocene, including the Medieval Warm period and the Minoan Warmth, which were both much warmer than today. Then as a third helping, be sure to follow the reading on how CO2 lags the beginning of warm period, proving it is the result of ocean out-gassing, and thus not causative of the warming. Don't let these climate activists convince you to stop thinking and let them alone determine the truth. That is religion, not science. You are intelligent. Read it for yourself. I did. That is how I became a skeptic. There are some good blogs which discuss all the recent papers, of which WattsUpWithThat is by far the most popular, and Judith Curry's site probably the most respected.

  4. Maju

    July 5, 2012 at 4:54 am

    Have you read both sides or only the Tea Party denialists? The "hockey-stick" graph is real and there is nothing absolutely nothing debunking it. Just some neofascist jerk paid by multinational oil and mining corporations (he's now member of the board of directors of Trelawney Mining and Exploration Inc. – no innocent hand at all!) and supported by the mass media. We know for a fact that almost every single glacier on Earth and even the Arctic itself is melting right before our eyes. Ask the Inuit, ask the Chagga who live under the shadow of the Kilimanjaro, ask the peoples of every alpine valley from Chile to Switzerland, from Bhutan to Idaho… ask the polar bears… I don't know who you are but I know that you are a naive right-winger (conservative or reactionary) who clearly hopes that the very concepts of (technological) "progress" and "growth" are real and not, as thermodynamics demands, mere extractions and transformations within the quasi-closed environment of Earth. We have transferred massive resources from Earth to the human sphere and that has brutal effects, climate warming being just one. Essentially Earth is in crisis and Humankind risks survival in this crisis we have provoked ourselves. Whatever the case there is nothing "necessary" in the hockey-stick shape (that's a fallacy) and there have been never, at least since the last glaciation, record temperatures like the ones we are experiencing in the last decade or two. Not even in the Neolithic climate optimum, which was warmer than anything else we know from Human (pre-)history.If things would be normal we'd be in the prelude of a new Ice Age… but things are anything but normal these days and we may be causing a climate similar to that of the Jurassic. That together with other man-made pressure to the environment (too much people, too much cattle, too much industry, too much deforestation, too many agricultural poisons…) is destroying species every day, leaving to our children an impoverished and highly unstable planet. And there is no alternative Earth.

  5. Caz

    July 5, 2012 at 1:41 pm

    Like I said, I read the peer review papers, not the politically digested forms. You should do the same. And if you think I am being paid by the oil companies, then please tell them to send the check. I have no received anything yet.

  6. Caz

    July 5, 2012 at 1:44 pm

    oh, and one detail…the Kilimanjaro glaciers returned recently. Their shrinkage in the 90s was proven to be due to drought, not climate change.

  7. Maju

    July 5, 2012 at 2:47 pm

    I meant McIntyre. You're obviously just a useful fool. A conservative naive who just wants that the things that he was taught and he likes like big wasteful cars are still ethically "good". I know the ones like you: you'll support any ideology that makes you feel better in your destructive way of life. "Wishful thinking for the win!", riiiiight?

  8. Maju

    July 5, 2012 at 2:55 pm

    Not sure about Kilimanjaro but notice that in 2008-2011 we were into the longest solar minimum in a century or more. As you may know (no, you probably won't, anecdotal data is your "friend") solar minimums cause temperatures to fall down quite a bit. And that's why the NW passage has not been opened since 2007 but will most probably be again this year. The solar cycle has 11 years and we are just moving away from the relieving solar minimum, what can we expect for the solar maximum of c. 2016? I'm rather scared. And the next solar minimum c. 2021 won't be as much relieving as this one was, most likely.

  9. Caz

    July 5, 2012 at 5:01 pm

    Aha!! My point exactly! Yes, it is the sun! It plays the major role, with CO2 a mere bit-player. Ocean currents and even H2O vapor play larger roles than CO2. Congratulations. You got there all on your own.

  10. Caz

    July 5, 2012 at 5:12 pm

    My, my, what assumptions you make about me. All wrong. And equating healthy scientific skepticism with radical denial of atrocities is both ludicrous and insulting. You do not win me over with that approach. Furthermore, you are breaking your own rules of decency, posted below. I do not want or expect an apology. I just want science.What I find interesting is that you display healthy skepticism when you comment on articles that you know a lot about (in paleontology). You make all sorts of valid criticisms and accept personal biases exist among the researchers that you are familiar with. I enjoy reading your blog for that reason. But for climate science, you treat it like religion – not to be questioned! Strange.

  11. Maju

    July 5, 2012 at 5:44 pm

    I have looked at the matter and I see absolutely NOT wrong the issue of unusual and very dangerous global warming with likely man-made origin (CO2 and such). You know planet Venus, don't you? Neither you nor that mercenary McIntyre have ever posited a single reason or even a single clear hypothesis, all you guys know how to do is to say "hockey stick", as if that would make any sense. I have a brother who is engineer (and hence should known better) who does exactly the same (because he's conservative-reactionary). He has no idea of the alleged science behind, the same you don't but he WISHES that McIntyre would be right, exactly the same he WISHES that Christian preachers would be right about life after death…All wishful thinking. Convenient self-deceit.

  12. Maju

    July 5, 2012 at 5:47 pm

    The Sun has cycles, notably the 11 year cycle and it is well known that it does affect average temperatures (higher in the maximum and lower in the minimum). So the unusually intense and long 2008-2011 solar minimum should have been very cold, everything else equal. But, as we are immersed in massive man-made global warming, it was just mild, average, it barely pushed warming back a tiny bit… Now that it's over, beware!


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