Melt pond May alliterates well and the name conveys what it's about: the time when melt ponds first start to form. Luckily, a couple of weeks ago, someone on the forum (forgot who, but thanks!) helped me find a perfect alliteration for June: Junction June. This name refers to the month's importance for the rest of the melting season.
The idea is simple: the fraction of the ice pack's area that is covered by melt ponds during May and June, preconditions the ice for the rest of the melting season, because melt ponds lower the pack's albedo and thus soak up more solar radiation. This in turn increases melting momentum, which can sustain a high decrease during the second half of the melting season, even if weather conditions aren't perfect for melting, compaction and transport. Conversely, if melting momentum is low, chances of new September records are minimal, unless weather conditions during July and August favour huge losses. Hence the word 'junction'. The trajectory for the melting season is largely determined during May and June.
Just like last month, I'll analyse the melt pond situation by comparing this year's weather conditions with those of previous years that generated records (2007, 2011 and 2012) as well as rebounds (2013 and 2014). But first I want to look at the melt pond distribution maps that were sent to me by David Schröder from the University of Reading and are based on his research published last year. A model, using NCEP reanalysis data for atmospheric forcing, simulates the melt pond distribution across the Arctic, and although pond area in May is only around 1% of the total melting season area, this melt pond cover fraction according to Schröder et al seems to have the strongest impact on the sea-ice state in September.
This correlation has been contested in a recent study by Jiping Liu et al, published in Environmental Research Letters back in May. The paper states that "a significantly strong relationship (high predictability) first emerges as the melt pond fraction is integrated from early May to late June, with a persistent strong relationship only occurring after late July." Either way, late June is now well behind us, so here are the melt pond distribution maps for 2012, 2014 and this year (click for a larger version):
Mind you, these maps are model results and don't display the exact locations of melt ponds.
Eyeballing the maps it's clear that 2015 has more melt ponds than 2014, but doesn't come even close to 2012. Dr. Schröder writes:
I just submitted our SIPN SIO prediction: 5.27 +/- 0.44 million km^2.
Very close to 2013 and 2014, but considerably larger than in 2012. Although the air temperature was generally higher in June 2015 than in 2014, the melt-pond area in May and June is very similar to 2014 and below the 1979 to 2015 trend line. This is mainly due to a lower fraction of thin-ice in our model simulation in comparison to previous years.
Basically, if I've understood correctly, the difference in melt pond cover fraction is compensated by the fact that the ice is thicker on average than last year. That makes sense, as 2015 is still behind last year when it comes to total volume, as calculated by the PIOMAS model (see latest update).
Let's have a look at what temperature anomaly and average sea level pressure have been doing during June. Again, I've divided the month up into two halves, and here's the first map for June 1st to 15th:
It's clear that the first half of June this year was warmer than in 2013 and 2014, and the SLP map shows a beautiful Dipole configuration with the Arctic perfectly divided along the prime meridian, with low pressure on the Siberian and high pressure on the American side of the Arctic, leading to the only period so far this melting season of serious sea ice transport through Fram Strait. It's also clear that 2015 doesn't come close to the relative warmth of 2007, 2011 and 2012, the years with the lowest September minimums on records.
Here's the comparison map for June 16th-30th:
Practically all the maps look cooler in general, compared to the first half of June. 2015 has all of the heat concentrating on the Pacific side of the Arctic, where most of the action has been so far this melting season. Lots of cold around Hudson Bay, where the ice still hasn't melted out. Again, if you look at years like 2007 and 2012, there is much more heat on the periphery. 2015 doesn't do better than 2013.
Over all, weather conditions during June echo the model results, leading us to conclude that not much melting momentum has been built up during these crucial first two months of the melting season. It resembles the past two rebound years, meaning there is virtually no chance that new records will be set in September. The main question now is: will 2015 be another rebound year or will it end up lower than 2013 and 2014?
Of course, there isn't a clear cut-off date for melt pond formation and its inertia-like effect on the ice pack. Subsequent weather conditions still play an important role. This melting season, for instance, has run quite a bit warmer than 2013 and 2014 so far, and although the effects of this have taken a while to show up, they are doing so now with a vengeance on our third piece of evidence: compactness maps.
As I wrote last month:
Compactness is calculated by dividing sea ice area numbers with sea ice extent numbers, which gives us a percentage. Short explanation: the Arctic is divided into grid cells. When 15% or more of a grid cell is covered with sea ice it will be counted as 100% covered with ice for extent (meaning the total km2 of the grid cell will be counted for total sea ice extent), whereas the exact amount of km2 that is covered with sea ice will be counted for area. This means that area will always be lower than extent, because of leads or open water within the grid cell.
Here's the thing: melt ponds fool the satellite sensors into thinking that there is open water where there is none. This will get counted for area, but not for extent (unless a melt pond is so big that the 15% threshold is passed). So, if there are a lot of melt ponds, area will go down faster than extent, and the percentage will drop.
Here's the latest CAPIE graph (Cryosphere Today sea ice area per IJIS sea ice extent) I use for the bi-weekly ASI udpates:
From being highest at the start of June, the 2015 trend line has dropped quite a bit to the middle of the pack, and now halfway July it is one of the lowest on record. In fact, the compactness graph below, made and updated by commenter Wipneus, that uses SIE and SIA data with higher resolution (smaller grid cells) from the same data providers, shows 2015 dropping to record low levels:
This is partly caused by large-scale divergence on the Pacific side of the Arctic, as the multi-year ice there is interspersed with first year ice that is melting out, and there isn't much of a compacting wind blowing. On the other hand, melt ponds also heavily impact the percentage, as a massive heat wave has been pounding the ice from Greenland to the Chukchi Sea, with the Canadian Arctic Archipelago and the Beaufort Sea in between, for the past two weeks (and forecast to continue for a while longer, though less massive).
Melting momentum is still being built up, but the question is whether this heat damages the ice enough for it to become visible in the extent and area numbers in August and September. If it does, 2015 will definitely end up below the past two rebound years. In fact, if these weather conditions persist, the trend line might even start to move towards lower years in the 2006-2015 period. But we'll have to wait and see if July and August weather can compensate for the lack of preconditioning during May and June. More on that in the forthcoming ASI updates.
CAPIE is biased high due to the 2 or 3-day lag of CT data, right?
Posted by: Nightvid Cole | July 16, 2015 at 14:08
Well, there is no more lag now that Wipneus pre-calculates CT data based on NSIDC extent data. But I divide SIE numbers by the SIA numbers on the same date. CT SIA dating is a bit confusing so there might be a 1-day offset.
Wipneus' compactness graphs are superior, because of lower resolution and SIE and SIA coming from the same provider.
Posted by: Neven | July 16, 2015 at 15:10
It's been pretty cloudy and foggy over the Beaufort Sea for the last ten days or so. Otherwise the Arctic ice map would be showing a truly scary 2012-ish shape.
Posted by: navegante | July 16, 2015 at 16:54
It's getting more and more of that heat now. The Bremen maps show continuing melt despite the cloud cover and a tendency to an early Northern Sea root being open fairly soon.
Much more interesting season this year storms or not...
Posted by: NeilT | July 17, 2015 at 14:52
I'm intrigued with the Beaufort Sea. With the thin ice melting away the embedded chunks of MYI are becoming increasingly surrounded by water. This way the shoreline of the Beaufort ice is becoming almost infinite. It will be interesting how that influences the melting process there.
Posted by: Joe Wentrup | July 17, 2015 at 19:32
I think that there are at least two variables which are not being considered when trying to correlate June melt pond fraction with September area/extent.
The first is snow cover, - one might speculate that snow changes in volume more quickly than ice, allowing voids to form on top of lower-lying areas of the ice surface, which can fill with water to become ponds. This prompts the question "what if there isn't any snow?" (as was the case with much of the anomalously low June melt-pond area depicted for 2015)
The second is the ice surface topology. Most of the ice which had anomalously low melt-pond fraction in June is FYI which formed is Sep/Oct/Nov/Dec last year - it therefore has a relatively uniform surface with no ready-made depressions in which liquid water can accumulate.
Considering the above it seems to me very likely that the June melt-pond fraction won't be a reliable prognosticator this year...
...and I think that this is starting to become evident even from just eyeballing EOSDIS/worldview. E.g. Look at the current state of the CAB north of Laptev at around 85 degrees N - there's a large area which looks similar in condition to fast ice in the southern laptev just before it dissolves into nothing. There's a slightly less dramatically rotten, but huge, area along a 100 mile long strip running E-W north of Greenland - just above the boundary between MYI & FYI.
I guess what I'm trying to say is, we know that this year weather has strongly favored melt across much of the arctic. We can't see it but that doesn't mean it's not happening. We don't have direct instrumentation over most of those areas - and none in FYI. We rely instead on proxy observations, such as melt ponds - but this might cause us to be misled because they are only reliable if we've considered all the variables.
Just going by the weak winter (over the CAB, at least), and the strong summer, and the evident mixing of air and water between the northern and southern latitudes, conditions have been just about perfect for creating a huge surprise for anyone who relies on estimates of ice formation and melt progress which were validated in an earlier era. Unfortunately, that's all of them.
So as seems to have become a habit of late, I'm not saying it's this year it largely goes poof - but I haven't yet seen anything to rule it out...
Posted by: epiphyte | July 18, 2015 at 03:41
the ice in the north end of the North West passage seems to be breaking up quite dramatically at the moment the fixed ice front has moved south by about 200km in the last week or so.
Posted by: philiponfire | July 18, 2015 at 10:14
sorry poor wording, I mean the edge of the unbroken ice has moved south by 200km and it looks as though there will be more breaking up in the near future significant cracks even further south.
Posted by: philiponfire | July 18, 2015 at 10:17
i do not often comment as I do not have any expert knowledge to impart but I think that it is worth observing that this year will not be the next new record minimum that title will probably go to September 2017.
I think that too much emphasis is being placed on the three most common metrics for measuring the state of the ice in a time when they are no longer as important as they once were. I think that focusing on these things tends to blind people to the real world. since a significant part of all sea ice is now first year ice which breaks up easily exposing any chunks of older ice to nice warm water is it not likely that the Beaufort sea will melt out more or less completely. Look at its visibly shattered state rather than thinking about its theoretical thickness.
Sea ice area is going to drop to 3.1 million km +/- a margin for a weather event with an appropriate extent to match. here is today's AMSR2 graphic.
ftp://ftp-projects.zmaw.de/seaice/AMSR2/Arc_latest_yesterday_AMSR2_3.125km.png
if you compare this with the same graphic for similar dates for the last 2 years this year is significantly more blue.
It is my opinion that there is an approximately five year cycle superimposed on the downward trend in sea ice extent/area.This is what my brain sees when I look at graphs of recent years.
I would put money on 2017 being the next record unless it is interrupted by a weather event, such as that which created 2014.
Posted by: philiponfire | July 18, 2015 at 10:46
http://arctic.atmos.uiuc.edu/cryosphere/arctic.sea.ice.interactive.html
shows how much both 2013 and 2014 were weather events and not long term climate. both had an anomalous long pause in the melt beginning at about day 200. this has not been seen in any other year in the satellite era if my reading of the graphic is correct.
Posted by: philiponfire | July 18, 2015 at 10:54
Is the ARC-HYCOM ice thickness map trustworthy in general? Although the other values (ice volume, area, extent) point to another rebound or at least remaining at 2013/2014 levels, the map shows less ice that's thicker than 2 meters (some of that had just thinned drastically in the Beaufort). If thick ice is waning, wouldn't that mean the arctic still becomes more vulnerable to weather events?
Posted by: AmbiValent | July 18, 2015 at 12:30
AmbiValent - See this exchange on the HYCOM forum:
https://groups.google.com/a/hycom.org/forum/#!topic/forum/5Zw5E0-3peU
and the related ASIF thread:
What's wrong with HYCOM?
Posted by: Jim Hunt | July 18, 2015 at 13:16
Ambivalent, I have no ambivalent feelings about this year's minimum extent well below rebound years'. The devil is on the details.
Posted by: navegante | July 18, 2015 at 14:44
Calling 2013 and 2014 rebound years implies a reversal of climate please point to one single piece of evidence that supports that idea.
there is clear evidence that this was in both cases a weather event superimposed on the ongoing trend.
why is it that so many people go charging off searching for unicorns when there is a bloody great elephant in the room?
Posted by: philiponfire | July 18, 2015 at 16:40
I don't agree, Philip. A rebound is not the same as a recovery. It is 'normal' for sea ice to rebound after a record, especially after record smasher 2012 (which, of course, was also a weather event on the ongoing trend, if we're going to look at it that way).
Posted by: Neven | July 18, 2015 at 16:45
I (for myself) was not implying that a reversal of climate had happened before.
If I understood well, calling for a reversal of climate would take like 30 rebound years.
10 would make one slightly suspicious of something
15 would make one say like what the hell is going on
30 and that's it, the sun or whatever is saving our skin
:-) kidding obviously, I don't have a clue on what would take for scientists to call for a climate reversal, but surely two or three years of cooler Arctic doesn't make it.
Posted by: navegante | July 18, 2015 at 17:57
Weighing in on the discussion, I’d say that MODIS now ‘s reflecting pretty much 2012 features. As Baffin fast-ice is now collapsing, Hudson Bay is discharging it’s ice cover within the next ten days, extent data should rapidly line up with the record years.
In the Pacific sector, ice quality is deteriorating at a freightening speed. As it is, ECMWF forecasts a lingering dipole config for about a week. After that period, Lows should take over reign in the CAB. Some stability might re-appear then.
Nevertheless, extreme Pacific SST’s are making their call in the Arctic. In the line of my earlier thought, there’s a perfect fit for this season. It is paving the way for continuation of the fast downward trend and maybe a ‘black swan’-event in ’17. It might even be ’16.
There’s not much solace in any news, these days…
Posted by: Werther | July 18, 2015 at 23:28
Personally when talk of "rebound" or "Pause" or anything else is going on about the Arctic Ice, I tend to go back to this link pop it up to normal size then run it from left to right.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/sea.ice.anomaly.timeseries.jpg
I think it would be better to rename "rebound" to "Return to the long term trend".
Because, as this chart shows, that is exactly what it is doing.
Also another salient point to note with this chart is that the trend is from 1979 to 2008 and the anomaly is measured from that trend.
Were the trend to be 1979 to 2000, then the result would be a hell of a lot more alarming...
That tape also, very clearly, shows 2012 as the outlier it really is.
Another thing I like to note with that anomaly chart is where it enters -1 and where it exits it again for the year. This, to me, is important because that is where the majority of the energy is sucked up by the sun.
Notably there is a clear departure from previous years/decades at 2007 and onwards. I shall be watching it again this year. But I won't be expecting much, I will be willing to be surprised.
Posted by: NeilT | July 19, 2015 at 00:26
An illustration to my post last night on the rapid line-up with 2012:
The > +4dC anomaly North of Ellesmere through July hurts where it is worst. In this 350K km2 the heart of the remaining MYI is losing volume at freightening speed. The well known structure, large rhomboid floes up to 1600 km2 within broad leads, is gone. It has taken on the form common in more peripheral parts of the sea ice over the last years. It is desintegrating into loose floes in large debris fields. And these are blue with melt ponds and even taking a brownish hue, like in the Chukchi Sea days before complete melt out.
This weather pattern and location hasn’t occurred before. I’d call the ‘black swan’ event if it were 2017…
Posted by: Werther | July 19, 2015 at 09:28
The critical factor we know nothing about at this time is the late summer heat.
http://ocean.dmi.dk/arctic/plots/meanTarchive/meanT_2012.png
2012 was the hottest year across the Arctic from Jun to Sept by a considerable margin of about 0.5 degrees Celsius. The melt ponds came early and the heat only dropped near other years in August. Comparing it to other years on the DMI graphs shows only 2007 had similar late heat above 80N.
http://ocean.dmi.dk/arctic/plots/meanTarchive/meanT_2007.png
This year June temperatures recovered from a very cool May to be very close to warmest in June. DMI suggests July has continued this trend.
If the El Nino has any impact by holding temperatures high from now to the end of September we could easily see extent drop down between 2007 and 2012. Currently an average season would take us near 4.4 M Km^2 if we accept that the Hudson/Baffin bay anomaly will disappear soon.
Posted by: DavidR | July 19, 2015 at 10:49
Hi DavidR,
I agree in larger terms with your posting. Still, although 2012 shows some warmer anomalies in the end July-end August period, the challenge is not that big. 2015 only has to continue some +1-+2dC anomaly over the CAB. That doesn’t seem to be a difficult benchmark to keep up to, given world-wide higher temp and a probably extreme ENSO event.
On top of that, the present two-three weeks spell of +4dC anomaly is located exactly over the ‘last stand’ of MYI.
Further, the ‘killer’ for ’12 was the GAC2012 storm between 5-10 August that year. The somewhat higher temp anomalies weren’t enough for the record minimum on a stand-alone basis.
Posted by: Werther | July 19, 2015 at 11:33
Of course we do have to remember that the state of the MYI at the beginning of 2015 is somewhat different to the MYI state at the beginning of 2012.
Which should, if all things are even, produce a different result with similar input...
Posted by: NeilT | July 19, 2015 at 20:20
Does anyone have a list of dates for when the Northern Sea Route has gone ice free? I don't have a source handy but IIRC the first time in recent history it opened up a completely ice free passage was 2007 and the pattern has repeated in some of the years since then but not all. It looks to me as if an ice free pathway is about to open and I wish to compare dates over the last decade for when this has taken place.
Posted by: Tanada1945 | July 20, 2015 at 09:45
Tanada - How do you define "ice free"? Whether the NSR is navigable depends upon the ice class of your vessel and whether you have assistance from the likes of "50 Years of Victory" or not.
https://youtu.be/VVtDX46cTJQ
I'm not aware of any "official list", but here's some handy links plus videos of ice movement along the NSR from 2012 onwards:
http://GreatWhiteCon.info/resources/arctic-regional-graphs/northern-sea-route/
Posted by: Jim Hunt | July 20, 2015 at 10:40
Jim I was thinking in the context of standard hull cargo ships being able to pass through with an ice breaker escort that doesn't have to break them a pathway at any point in the journey. I think it would be foolish to take a standard hull ship through without an escort and if you go around that side Russia demands an escort be along in case of trouble. Not too long ago China, South Korea and Japan were exploring regular transits as a way to save time and money on shipping to Europe. China even went so far as to send their own icebreaker through the passage to gain real world experience.
Posted by: Tanada1945 | July 20, 2015 at 19:26
Werther,
2012 was 0.6 dC higher than the next hottest year in June and September across the Arctic circle and 0.3 dC in July. This may not seem like a lot but in both cases the next 7 hottest years were all within 0.6dC of the second place getter.
The hottest August was 2007 which was 0.3 dC warmer than 2012.
If July and August are both 'hottest on record' this year, then we could end up anywhere (low).
Posted by: DavidR | July 21, 2015 at 05:41
Jim Hunt wrote:
Indeed.
Back in 2012 [IIRC] there was some commotion when from June on the Russian government introduced a regular traffic of mammuth tankers from Murmansk to the East, over the North-East route of course. Tankers escorted, preceeded, by the atom ice breaker Jamal. Moreover, from 2017 the traffic will be continued all the year around when a new atom ice breaker will be ready, an atom ice breaker custom builded to the job.
Other than that, already in 2009 the Jamal escorted two German cargo ships over the North-East route to the Bering Strait.
Bottom line, this isn't even an issue anymore.
Incidentally, some of the Russian mammuth tankers are ice breakers as well, and we really don't know what they are doing all the time, do we? :-)
Posted by: Kris | July 21, 2015 at 07:34
http://eh2r.blogspot.ca/2015/07/it-seems-already-time-to-pronounce-bye.html
My confidence grows day by day, 2015 exceeding 2012 record low minima should happen, will not wait much longer to make a non official declaration in advance, the only thing to stop this from happening would be massive clouds coverage from now on.
Posted by: wayne | July 21, 2015 at 09:41
I don't think 2015 will break the 2012 record. The melting season simple started too late and progressed too slow during June to break that record.
But there is so much fragmented ice at the ice margin and lower elevations, that it seems pretty clear that area and extent will be going down pretty steeply for quite some time.
This (low concentration in the ice margin) is also apparent on the low resolution observations as we can see from Wipneus' concentration graph :
https://sites.google.com/site/arctischepinguin/home/amsr2/grf/amsr2-compact-compare.png
So I don't think there will be any slow-down over the next couple of weeks, as we saw with 2013 and 2014.
Posted by: Rob Dekker | July 21, 2015 at 10:28
Rob Dekker wrote:
Still to early to call. Remember, in 2012 mid July we had about the same situation as it is now, with the difference now the Beaufort side is even more fragmented.
Remember, in 2012 the turning point came with “the storm” in early August, a cyclon which scattered the entire Arctic apart.
So, “to storm or not to storm, that is the question.” And to be sure we'll have to wait till August as usually only then this type of cyclons can enter the Arctic.
Posted by: Kris | July 21, 2015 at 12:35
Kris, a Cyclone similar to August 5 2012 is likely, but its the pre- existing ice conditions which matter.
"So I don't think there will be any slow-down over the next couple of weeks, as we saw with 2013 and 2014."
2013 was very special Rob,
there was a huge melt in place with literally no compaction, 2014 had a blitz melt later in August which was very impressive. I have added and collected the evidence:
presently:
http://eh2r.blogspot.ca/2015/07/it-seems-already-time-to-pronounce-bye.html
and here it is as was in 2014:
http://eh2r.blogspot.ca/2014/08/7-day-ice-melt-as-fast-as-it-goes-but.html
and here
http://eh2r.blogspot.ca/2014/08/spontaneous-meltdown-matter-of-ice.html
However, there is no indications for 2015 to go down significantly below 2012, there was a substantial consolidation and strengthening of sea ice over the main pack during the winter just past at about the Arctic 90 degree longitude region. Remaining sea ice appears to be still quite potent, and can literally replenish itself by stimulating favourable weather patterns. When weather won't matter anymore then a yearly melt season "crash" will occur.
Posted by: wayne | July 21, 2015 at 17:15
A new James Hansen Analysis
I have not seen this mentioned before, but apologize if I missed it.
There is only press reporting, not the article.
http://www.slate.com/blogs/the_slatest/2015/07/20/sea_level_study_james_hansen_issues_dire_climate_warning.html
The assertion is that the sea level rise for the next 50 years is likely to be ten feet or more, not one foot. Your mileage may vary.
Posted by: George Phillies | July 21, 2015 at 19:30
A new James Hansen Analysis
I have not seen this mentioned before, but apologize if I missed it.
There is only press reporting, not the article.
http://www.slate.com/blogs/the_slatest/2015/07/20/sea_level_study_james_hansen_issues_dire_climate_warning.html
The assertion is that the sea level rise for the next 50 years is likely to be ten feet or more, not one foot. Your mileage may vary.
Posted by: George Phillies | July 21, 2015 at 19:30
Wayne, the way you put it, robust ice induces preserving weather, so next season even more robust ice.
I think very warm weather sustained during a season may bring the crash one of these years because the Earth climate is getting warmer and warmer. So bad warm weather is most important for the crash (and I mean weather, caused by warmer climate).
I no longer believe in the "ice is so thin that weather does not matter" as I used to before 2014.
Posted by: navegante | July 21, 2015 at 21:22
I assumed this was the case because of events during the 2011 and 2012 melting seasons. This depends, of course, on initial ice thickness. But preconditioning plays a very important role after that.
Posted by: Neven | July 21, 2015 at 21:29
Yes, I admit I am following your current of thought because it makes sense to me.
Posted by: navegante | July 21, 2015 at 21:32
Navegante: "robust ice induces preserving weather, so next season even more robust ice."
Not quite, the extent of very resilient thick sea ice matters,
so say 2015 minima beats 2012, the holistic effect of sea ice as part of Earth's climate system will be less important as a result. Size matters.
Posted by: wayne | July 21, 2015 at 23:19
George Ph notes: "A new James Hansen paper with 12 co-authors... Lots of press reporting, not one person links to or quotes from the article.'
Because no one has seen the article. They screwed up royally by sending out the press release without an embargo contingent on article release. It is not available at Hansen's scholarly publication sites nor at ResearchGate.
It is supposed to be released sometime "this week" at ACPD; by then the media cycle will have moved on, way on. We'd all be hollering foul play if the Southern Corp does this with Willie Soon's Nov 2015 paper.
The link to the paper should be:
http://www.atmos-chem-phys-discuss.net/papers_in_open_discussion.html
Posted by: A-Team | July 22, 2015 at 03:09
That's a great paper, even if it reads more like several different but related papers. The have exponential extrapolation of freshwater input in a way consistent with modern measured values and Eemian sea levels leading to flat global temperatures at the current time, which later turn downwards. This is due to high heat flux to the oceans. The warming at the base of Antarctic glaciers makes it potentially self-consistent.
Posted by: Blaine | July 24, 2015 at 11:10
I agree, Blain. What a wonderful read.
For the record, here is the paper in full :
http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015.pdf
What I find especially important about this paper is that it addresses several issues that have been points of contingencies in discussions with 'sceptics'. Such as :
Which points out clearly that if we worm our planet a bit more than we already have, that there will be serious concequences.
and
which clearly addresses the issue of why Antarctic ice extent appears to be increasing while Antarctica (and the planet) is warming.
and
Which explains why CO2 is lagging behind temperature in the paleoclimate record (an issue which was brought up time and again in discussions about Al Gore's movie), while emphasizing that CO2 is the control knob on global climate.
and
Which re-states that we should not expect the same "millennial" timeframe delay in climate change now that we are increasing CO2 levels directly, and instead we should expect an exponential (doubling time of 10-40 years) increase in ice sheet melt, going forward.
and finally the statement that Earth's energy imbalance is crucial in what we can expect to happen in the near future :
And that was just the abstract. Massive amount of evidence in the paper itself.
Posted by: Rob Dekker | July 26, 2015 at 11:51
An epic paper if you ask me.
Posted by: Rob Dekker | July 26, 2015 at 11:54
At 121 pages this is going to take me a while to get through, reflect upon and consider before I can offer opinion.
One problem I have always had with using past rapid sea level rise events is that the Laurentide and Eurasian ice sheets (+Greenland + Antarctic) were far more extensive than just Greenland and Antarctic now. So there may have been an increased opportunity for rapid sea level rise by virtue of that, and drawing direct analogy may not be sound. I don't recall that being addressed in the past Hansen papers on this issue, I haven't read enough to say whether it will be in this (page 10 and I have some other work to do).
Posted by: Chris Reynolds | July 26, 2015 at 13:19
Chris,
Antarctica is quite a bit larger than the Laurentide ever was.
And in the paleo-climate record, Antarctica's ice sheet seems to be mostly regulated by CO2 levels instead of insolation.
So Hansen has a point that Antarctica's ice sheet may be subject to exponential melt, not inhibited by the millennial delay that used to regulate ice sheet decay, now that CO2 levels are way above where they ever were during the Eemian.
Either way, the nice thing is that this is a "discussion" paper, and several comments have already been posted :
http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015-discussion.html
Posted by: Rob Dekker | July 28, 2015 at 10:07