SATire, have you read the paper? The material you seem to think is missing is thoroughly referenced. It's not *discussed* to speak of, but then it would be surprising for it to be given that the paper has a different focus. A vast amount of research has come before, as is obvious from the paper's extensive (>100) references. You might consider reading up on PRISM and PlioMIP in general. Anyway, it looks to me as if you may have run into some people who mainly wanted an argument. If that wasn't the case, it seems like they would have noticed that the science points strongly away from tectonically-driven circulation changes as a major cause for the cooling, and toward reduced CO2 as the primary cause of the circulation changes.

To repeat the point for those above who missed it, the video is discussing a paper prior to the one that was just published. SATire, the key point missing in that discussion is that global/polar temps *increased* from the Zanclean through the mid-Piacenzean even while the Central American and Indonesian seaways were completing their process of closure. Note that the deep currents would disappear earlier than complete closure. The mid-Piacenzian warming is basically not explainable by anything other than CO2, as demonstrated IIRC by several recent modeling studies. There's been a huge amount of other recent progress in the study of the detailed causes of Pliocene warming, which I suggest you catch up with. I'll save you some time by pointing to Hansen's latest. Note also that even the material you linked to claims a climatic effect of seaway changes primarily by way of affecting atmospheric CO2 levels, rather than a more direct mechanism. The introduction to Etourneau et al. (2009) makes this point unambiguously. Neven, all of this confusion makes me think you should clarify the foregoing in the post and put a label on that second graphic. You've done a great job so far, but I'm afraid it takes eternal vigilance to keep this blog from dissolving into amateur hour. Alex, just to be clear on this point, the major difficulty with the second graphic isn't so much the 2100 date (although that is a problem, even presented notionally), but that you're comparing Arctic-wide apples with the relatively cool Lake E orange. Ultimately we would expect ~400 ppm at equilibrium to get us to more like +~18C in the high Arctic (based on recent results from northern Ellesmere, note immediately adjacent to the sea ice "refugium" and the GIS). BTW, I need to now take the time to re-read everything more carefully myself since all of this material doesn't sink in all that well on a first pass, but my impression is that the key novel finding of the new paper is not that the Arctic was very warm (we've known that for years) but that the Lake E record shows relatively (and surprisingly) little effect from Milankovitch cycles (as opposed to more recent times, e.g. MIS 11 and 31 as discussed in the video). The important implication is that the CO2 is very dominant indeed, and that NH Arctic ice (all of it) and the WAIS simply disappear at current CO2 levels. Oops.

Congrats, Neven! It's quite the milestone. Just to be clear, the video discusses a phase of research prior to the current paper. Alex, are those your graphics? In any case the second one showing a +8C rise by 2100 is misleading in that there's no basis for saying what date it will happen by. Also note that the +8C is specifically for the Lake E site, which is a somewhat continental location on the edge of the Arctic and so on the low side for an Arctic average.

Erimaassa, I expect that part of the point is to study the spread of responses in regard to such things.

Speaking of consensus, it looks like Springer is providing a useful service in issuing open-access summaries of the state of the science within each Earth Science specialty (many, but not all, will pertain to climate science). The new polar science one is further organized by sub-specialty, each containing a brief discussion of the science and (most valuable IMO) links to a number of papers comprising the state of the science. It's short enough so that someone unfamiliar with the field can acquire an overview in short order. Apparently the plan is to update annually. It seems worth highlighting here, Neven. I should add that IMO this is more or less what the IPCC should be doing, noting that after seven years of waiting the forthcoming WG1 report section on Arctic sea ice looks likely to be a virtual dead letter upon issuance as a consequence of publication lags, scheduled as it is to be made public within days of the likely 2013 minimum. (Check out the IPCC front page just now, BTW; someone there at least has a sense of humor.)

Remko, relative to recent years there's nothing unusual about the drop so far. It would become notable if it breaks out of the pack of prior year trends before June 1 or so, but even if this turns out to be an extreme melt year that might not happen.

"I'll nag TypePad about that as soon as the spam system works properly." It may not be the Arctic Ocean, but I'm very confident something will be frozen over when that happens. :)

You seem to have misunderstood me, sofouuk. I mentioned China because of all the major countries with the capability of undertaking a project like sulfate geoengineering on their own, they're the one that's most under the gun in terms of climate change impacts. It sounds as if you might not have been aware of that. Re the nukes, while a nuclear war will remain possible so long as the weapons remain, my point was that such intimidation would be ineffective against them (as would any form of military intimidation). "Messy" was a reference to both the politics of such a circumstance and the consequences the geoengineering itself, although I could have been more clear about that.

Thanks for the Dyer link, Lodger. It's part of the view I've held for a while now, although of course he expresses it far better than I could. It's going to come down to sulfates, and I'm afraid that by then the amount needed to actually stop and reverse warming is going to have consequences even more severe than just letting the warming continue. But a country getting the worst of the warming impacts that has the technical capability to do the injection (i.e. China) indeed may just do it anyway (albeit badly since to be very effective the injection has to be done more or less evenly around the globe). And note they have nukes to defend themselves from anyone who objects. Messy.

Bear in mind that a number of scientists thin the weather link is to Arctic amplification generally rather than just sea ice loss. That makes it a lot easier to consider the effect on spring events.

Open a topic, Geoff, and note that there's been a huge amount of research on the subject in the intervening 6 years. It would be interesting to ask Bala how his views have changed. See this but also this, both published very recently. My impression from these and other results from the last few years is that new forests are a net plus with the benefit tapering off over time, but that the negative impact of a warming climate on existing forests is far larger.

Also, for much of the year at those latitudes albedo is either zero or small. For much of the remaining part there is little or no snow.

The Canute canard strikes again! :) As many will know, Canute in fact was proving to his suck-up courtiers, who apparently had gotten rather carried away with praising him, that any attempt to command the tides to change their behavior would be useless. Great graphic once again. Am I detecting a theme? :)

Sure, Vaughan, but also don't forget that spring and fall are poor times of year to look for temperature extremes, plus of course the NA West Coast is rather famous for having moderated weather most of the time. One can have an extreme anomaly (although I suspect your present weather falls short of that), as most of the U.S. did last year with a May-like March, but it won't be perceived as extreme because it's not in an absolute sense.

Just to add, this makes three Arctic land feedbacks that have had their warming effect calculated substantially upward recently: Vegetation, permafrost and microbial activity. GCM results for the Arctic don't include these at all since they're slow feedbacks, and to my knowledge ESM (earth system model) results have incorporated only the permafrost, and that only by way of the calculation in the paper describing the increase in the effect. And of course these three feedbacks will feed back on each other, so it will be interesting to see how the effects are handled.

The albedo effect is larger than any CO2 sequestration benefit, especially locally (since the CO2 is effectively drawn from the whole atmosphere). Vegetation that's taller than the snow is deep doesn't get covered very well.

Yet another near-future Arctic feedback has been found to be much stronger than assumed in the models. I have to say that at some point surprise becomes a difficult response to muster. Next?

Alexander, your interaction with your friend demonstrates yet again that many if not most people will be able to make light of even sharp changes in the Arctic unless there are clear, immediate implications that will impact them. So IMO we need to speak in terms of feedbacks that will affect crops via drought, floods and temperature excursions (mainly heat but still some cold, as we are seeing more and more). Europeans and Americans have lost their cultural memory of famine, so it's going to be harder to get them to pay attention.

Late snow means April flooding. Something to look forward to. Re the short-term ice trend, we, scientists and all, are just guessing at this point. All we really know is that GCM-based projections of a slow process appear incorrect. Maslowski's RCM -based projection may be correct, but just the other day he was lecturing Neven about jumping the gun on this stuff (although to be fair the context was Neven's question was about how soon the Arctic could go entirely sea ice-free). My personal guess at this point is to agree with A-Team, albeit with large error bars. :) But I'll repeat again the larger context, which is that the last time CO2 was ~350 ppm for any length of time Arctic temps were 18C +/- 4C greater than present, and the models are unable to replicate this even with varying assumptions about changed boundary conditions. Push on the Arctic and something big happens, and we don't really know what it is. We can't say for sure that we're seeing the beginning stages of a rapid shift toward such a state now, but nor can we say we're not.

SH, a lot like what we're seeing now. Those highs like to set up in a couple specific places, then everything else follows.

Could be a coincidence. Or not. What are the physics?

Ah, Venus on the Half Shell (for any Kilgore Trout fans present). IIRC it didn't start well.

Wow. Has this sort of cracking pattern been seen before at any time of year?

SH, ocean circulation is hugely critical to climate. Dumping a bunch of heat into the oceans is going to have effects, potentially ones worse than if it was going into the atmosphere. Melting ice is fun to watch and is certainly a visible canary in the coal mine, but the impact we care about most is shifting rainfall patterns affecting the crop-growing regions, noting that we're already seeing some of that.

Judah Cohen and colleague have a new open-access snow paper. There's an accompanying video, which is a nice added feature.