Can anyone tell me about Dansgaard-Oeschger and Bond events and their significance, if any, to this debate?

Question

I have seen these events proposed as an alternative explanation to the current warming trend that people like me accept as being due to increasing levels of CO2 and other greenhouse gasses in the atmosphere.

Now I would have thought that, for these events to be a reasonable explanation, there must be;

(1) Something wrong with the CO2 theory,

(2) Evidence showing that the D/O&B events are now driving the upward trend in global temperatures.

So, are they real events? … or just labels people have given to unexplained random changes in the past?

Assuming they are real events, what drives them and is there any evidence they are happening now?

Are they a better explanation of the recent warming than the increase in greenhouse gasses? ... and why? ... or why not?

Answer 1

While I think Dana's article overall is good, I think he missed the mark on several of his criticisms of the D-O events as related to the current warming. I actually commented as much on the original posting of the article (commenter RobertS), but they appear to have gotten lost in his link.



To answer your questions

1) They are real events, but there is conflicting evidence as to whether or not they are actually driven by a periodic forcing. See [1] and [2].

2) Scientists are unsure of their underlying cause at this point, but several recent articles (e.g. [1] and [2] again) argue that they are purely noise driven; i.e. no underlying periodic component. Their cause could range from things like the a sudden largescale influx of freshwater due to the breaking of an ice dam (e.g. Lake Agassiz), or a comet impact, as is a suggested mechanism behind the Younger Dryas event.



The fact is that the D-O events are likely unrelated to a underlying periodic forcing, as many so-called "cycles" were missed altogether during the last glacial period, and their interglacial counterparts (Bond events) have been virtually nonexistent. If a periodic component did exist, due to the reasons stated above, its magnitude must be so small as to render it nearly undetectable. This is the position taken in several previous studies which model the D-O events using stochastic resonance, whereby a *very* weak signal is greatly amplified by noise to send the climate over a particular threshold (see [3]).



=========

Ah, thanks Dana.



Jim,

No, I am not suggesting that D-O events are due to "quasicyclical comets or periodic freshwater flushing". Comet impacts and glacial dam bursting are but two examples of mechanisms that could cause the abrupt climatic shifts seen during the last glacial. I specifically stated that I believe D-O events unlikely to be related to a periodic forcing, but if they did contain a truly periodic component, the signal must be immeasurably small. That so-called "Bond events" have been virtually absent from the proxy record indicates either that 1) There is no real 1500 year cycle, or 2) the stability of interglacials preclude them from effects of any underlying signal, which must necessarily be non-terrestrial in origin. In any case, D-O "cycles" have nothing to do with the recent warming.



Sources

[1] Ditlevsen et al. (2005), "The Recurrence Time of Dansgaard–Oeschger Events and Limits on the Possible Periodic Component". Journal of Climate.

[2] Ditlevsen et al. (2007), "The DO-climate events are probably noise induced: statistical investigation of the claimed 1470 years cycle". Climate of the Past.

[3] Rahmstorf&Alley (2001), "Stochastic Resonance in Glacial Climate ". Eos.

Answer 2

Your first problem is that you are accepting the CO2 theory without any reservation. Then you want an alternative explanation to first prove your chosen theory wrong before giving it any chance of being correct. Why is it that you cannot open your mind to each, determine which has merit, and then make up your mind as to which is most likely or the best explanation? They are not mutually exclusive anyway. There seems to be a periodic variation in climate on the order of 1500 years. This isn't the only cycle that has been identified. There are several. What the D/OB demonstrate is that there is natural variation. It was rising and generally is continuing. You want to insert your CO2 theory onto that rise. I wouldn't pretend to know what causes D/OB but it sure doesn't appear to be CO2 driving them. The very most you could do is suggest that CO2 played a role in the last 50 years but that would be speculative on your part.



(You know I notice that every time Dana follows me, I get 4 thumbs down and he get three up) Coincidence. I think not. One thing it indicates is that Dana has an aversion to science facts.



<<< We aren't assuming the end of days, we are observing it. >>>

OOOOH that is convincing. The lack of scientific reasoning is breathtaking.



Bob, I hope you don't think is remotely plausible that they are caused by quasicyclical comets or periodic freshwater flushing. If there are periods when fresh water interupts ocean currents, why wouldn't that likely be caused from periodic warming. There is no evidence that I am aware of which indicates periodic daming and subsequent dam failure of glacial runoff. Where would this take place? Perhaps you are not suggesting these aren't periodic events. Clearly there is nothing that I know of that would suggest it is. I recently heard that a Tunguska size event happens every 1500 years or so but that doesn't mean it is cyclical.



You really have to wonder why people will see something happen over and over again and then after the last time it happens, they think they caused it. It is ridiculous in the extreme. That is what AGW boils down to, nonsense and nonscience.

Answer 3

"The argument that D/O events are causing or even contributing to the current warming is riddled with errors. "



The argument that CO2 is causing (all) or even contributing (well it is at least contributing some) to the current warming is riddled with errors (and assumptions and uncertainties).

Answer 4

I wrote a section on D/O events here:

http://www.skepticalscience.com/solar-activity-sunspots-global-warming-advanced.htm



The argument that D/O events are causing or even contributing to the current warming is riddled with errors. The timing is wrong, we appear not to be experiencing D/O events during the Holocene, and the factors we believe contribute to D/O events (i.e. changing solar activity and/or freshwater input into the North Atlantic Ocean) are not happening.



Again it all boils down to causality. The planet has an energy imbalance which has to have a physical cause. Even natural cycles like D/O events are physically observable. If global warming is being caused by D/O events due to changing solar activity, then satellites monitoring solar activity would be observing this change.



The only significant physically observable cause of the current warming is the increasing greenhouse effect. And that's where jim z gets it completely wrong. We're not assuming AGW, we're observing it.



*edit* bob, I linked to the rebuttal, whereas you commented on the blog post here:

http://www.skepticalscience.com/How-we-know-the-sun-isnt-causing-global-warming.html

Answer 5

if the Bond event is the postponement of James Bond #23 then i am really sad also