After bouncing off a pay-wall, I found: https://www.atmos.washington.edu/~david/Ding_etal_2016_submitted.pdf It may be an earlier draft of the published paper. Apparently a lot of folks are making claims that may be lifting parts out of context. Regardless, an interesting read but one sentence in the abstract is likely to attract attention: Because the observed circulation variability over the Arctic is inconsistent with the expected model response to anthropogenic forcing, a significant component of sea ice loss over the last three decades may have been driven by dynamical sources of natural climate variability. To me this suggests the gap between "weather" and "climate" is being used to suggest an alternate hypothesis of "natural climate variability." For us, this is a hypothesis but the paper has just signed up for defining something called "natural climate variability". I'm hoping @wxman will join in review as ". . . atmospheric general circulation model (ECHAM5) . . ." is mentioned early in the paper. Still reading the paper but it looks like they see a high pressure system over Greenland as forcing the bulk of the warming . . . right over the Greenland ice sheet. They go on: Model experiments32 show that about 50% of the circulation change and the associated warming over Greenland is attributable to natural variability originating from the tropical Pacific Ocean. An “ad hoc” attribution through a combination of these components suggests that ~30% (= 50% × 60%) of the sea ice decline observed since 1979 during JJA is attributable to natural variability in the tropical Pacific. This "tropical Pacific Ocean" effect is curious since it points back at the La Nina and El Nino area. I notice they also selected periods of actual observations that ended during the 'great pause.' Sure this could be just the data available. A better answer is to update their methods and use fuller datasets of actuals. They also concentrated on just the Summer warming and melt. It makes sense to see if the seasonal periods outside of this narrow window shows constancy as if the Greenland high plays no part. My personal observation has been the Arctic winter freeze takes a break every time there is a "Polar Express" that freezes the Northern land masses: North America, EU, Russia, and Asia. We literally see ice melting temperatures in the polar regions as the displaced cold air mass is replaced by warmer Pacific and Atlantic air masses. This also explains part of why Antarctica is running behind. The bottom line, I don't see how they replaced the 'tropical Pacific' for 'anthropogenic forcing'. I see how they took the sea ice cover to adjust the model . . . but that is only one factor and not the whole of anthropogenic effects. For example, how did the 'tropical Pacific' get that extra heat that apparently induces the high pressure system over Greenland? Bob Wilson ps. Insertion of "anthropogenic" in a paper describing a climate-weather effect suggests 'salting the paper' to get more eyes on it. As an undergraduate, I once wrote a paper whose obvious intent was to see if we would properly 'footnote' and a 'reference table.' I got my one and only English A by citing a recent issue of Playboy magazine. I'm sure the young graduate student instructor felt it important to check my source.
I strongly suspect Dr. Ding would send you published version when/if accepted in response to email. Email address you have. It would also seem a fair question why no newer NSIDC since 2014? I do not necessarily agree that Anthropogenic here is salting. What other term better describes +CO2 over the modeled time frame?
I know sometimes a reference is used to summarize common knowledge. They may have had a word count threshold. Just I think extraordinary claims need more than a reference to another paper. I hope @wxman joins us as I am wonder if high pressure is a secondary effect of denser, cold air? Greenland is a plateau, higher altitude and larger area than the rest of the Arctic circle. If high pressure is a by-product of cold air, a fundamental premise of this paper may bear a closer look. I am tempted to follow-up with an e-mail request for the paper. Bob Wilson
After a brief search of the "ECHAM5" GCM, it appears that it is a climate analog of the ECMWF NWP (weather) model. The ECMWF NWP model is relatively a very good global model. As far a high pressure relative to cold air, surface high pressure is correlated with cold air masses. "High pressure" in the upper troposphere is actually associated with warmer air in the column (upper high pressure = higher "heights"). Warmer air expands vertically causing the higher heights.
Ok, here is the note I sent: Hi Dr. Ding, Google recently pointed to an early draft of "Influence of the recent high-latitude atmospheric circulation change on summertime Arctic sea ice". Over in PriusChat, some of us started discussing the paper I stumbled across: Influence of the recent high-latitude atmospheric circulation | PriusChat What sparked my interest were the popular press descriptions of the paper conclusions. But when I read the early draft, a couple of things had me scratching my head: "natural climate variability" - the paper suggests tropical Pacific air is causing the high pressure centered over Greenland. Yet recently there was major storm system to the east of Greenland that push a substantial amount of Atlantic air over areas including the western Arctic and this appears to be an area that is suffering significant surface ice loss. Granted, one storm does not make a climate trend but the loss of eastern Arctic ice is significant and to get an Pacific air would require passing over central America and Mexico. That seems a stretch. I was especially looking for quantification of "natural climate variability" but other than El Nino/La Nina cycles in the Pacific, I didn't see the relationship and patterns in the paper. "anthropogenic" as referenced in the paper did not seem to have a lot of detail about the specific mechanisms. Not trying to be difficult but I think the paper could have made a stronger statement IF some descriptions of the specific effects were enumerated. For example, 'dirty snow' from soot is one such source but not mentioned in the paper. Some description of the anthropogenic effects in the paper would have been appreciated. I throughly agree with the 'high pressure system over Greenland.' Just I see it as a mechanism rather than a root cause of "natural climate variability.' IMHO, it looks like a similar mechanism that keeps Antarctica fairly frozen but we might discuss this another day. One of our collaborators suggested asking if I might get a copy of the paper without going through the 'pay wall?' There may be details that the abstract and Google revealed, draft paper are missing. Bob Wilson
A much better, layman's article: Up to half of Arctic melting can be explained by natural variations - CSMonitor.com Bob Wilson
Fastest reply to a "please send pdf" email I ever received was <2 hr. Time zone of recipient gave a mental image that he was sitting by computer (in PJs?) waiting for someone to ask... Your request is OK but no need to justify it at length. Just "send to me, thank you". For stimulating discussion part, you could be very brief down to the level of bullet points. Author may here have gone TL;DR on you.
The e-mailed paper included a 'press release' that didn't really change anything. Perhaps made the paper clearer for a lay audience, the 'Cliff Notes.' But having read and cogitated on the paper: "three months of summer" - in effect they windowed the models to just the summer melt season when in fact we know to have something to melt, you have to have something to freeze. It would be a better paper had it covered the full year and didn't clip out such a small part of the Arctic, annual weather. average of climate models - apparently the anthro data fed into their model came from the average of 32 climate models. This is so wrong because we know from the Berkley Earth model survey that some are better at global temperature predictions and others at regional accuracy. For example, a model for monsoon rain is pretty important to Asia and India but they are less concerned with the other contents. Had the authors used Berkley to identify models with better global and/or regional accuracy near the Arctic, it would have been better. A lot of work went into this paper but the methodology could be improved. Certainly, I think their "anthropogenic" descriptions need more meat. I would also share the climate science reports I've seen say there are natural systems at work and not exclusive CO{2} warming but sad to say, this report seems more about mechanics and less about what drives these natural systems. Bob Wilson
One issue that was addressed in the paper is whether the rising heights found in the Arctic region are causing the circulation changes/surface warming ("top down") or is the surface warming causing the rising heights ("bottom up"). According to the narrative on page 7, the authors conclude that the mid- to upper-level circulation changes/rising heights are responsible for the surface warming ("top down"), based on modeling exercises that were conducted. Thank you Bob for sharing this paper. I was not aware of the study previously.
