Arctic Sea Ice

June 2019, one hell of a month

Before the latest PIOMAS data are published, somewhere next week, I wanted to present an overview of all the things that have been happening in the Arctic these past couple of weeks, and what they may mean for the outcome of the 2019 melting season. You've guessed it, I'm going to be talking about melting momentum (for those not familiar with the concept, here's the archive). 

But I want to start off with something else. Almost every melting season is marked by some spectacular event nowadays. From the Great Arctic Cyclone of 2012, the huge cracking event of February 2013, the possibility to sail beyond 85N in September 2014, to the almost circumnavigation of Greenland in August last year. This year, another event has really stood out so far.

Every melting season, the entire North American coast clears of ice at some point, making it possible to sail from Bering Strait to M'Clure Strait (western exit/entrance of the Northwest Passage central route). Back in 2016, there was a chance of this happening record early, but it didn't pan out. This year it did, four weeks earlier than any other year in the Concentration Maps section of the ASIG. The event was reported by Rick Thoman (ACCAP) and Lars Kaleschke (University of Hamburg), both providing some great graphs and animations (see here).

Here's an animation of Uni Bremen Sea Ice Concentration maps showing how it all came about (we even had a great poll on the ASIF to speculate about the date when there would be open water all the way):

But just one event does not a record melting season make. What does make a record melting season, is melting momentum. Here follows a barrage of maps and graphs, with short commentary, to give you an idea of how the 2019 melting season stacks up so far (click on the images for larger versions).

As we approach the final stretch...

For years we've talked about one of the most fascinating phenomena of Arctic sea ice loss as it progresses from year to year: The moment when the ice disappears regardless of the weather. We've seen some of that, back in July 2012, when extent and area numbers kept going down steadily, even though weather conditions weren't conducive to melt and should have caused a marked slowdown on the graphs (like they did in the preceding years). Some time later I concluded that this had to do with what I now call melting momentum.

The idea is that if during May and July the ice gets hit by lot of sunshine, lots of melt ponds form and they soak up a lot of heat. This doesn't immediately cause the ice to melt, but starts to make itself felt towards the later stage of the melting season. The built-up momentum keeps the melting going. For this reason I've been focusing on things like compactness, that tells us something about the amount of water within the ice pack, whether open water or melt ponds (satellite sensors can't see the difference).

But does this still hold true? Will there be a moment when the ice disappears regardless of melting momentum as well? We saw in 2016 that there wasn't much melting momentum built up during May and June, but despite the cloudiness, a record warm winter and persistent high air temperatures were enough to make the ice vulnerable enough for a big cyclone and massive dipole to have 2016 come in second on almost all graphs (see this overview). Yes, melting momentum is important, but there are other things at play as well, of course.

NSIDC Compactness (are divided by extent) as of July 29th

Now, this year has been extremely interesting so far. For the third time in a row, the winter preceding the melting season was relatively mild, the maximum was low (second lowest on record), and the trend line on many a graph went low from the get-go. Not as low as 2016, but low. However, as in previous years, clouds moved in and things slowed down to a crawl, taking the trend line as high up as 11th lowest on record on the JAXA sea ice extent chart last week. But then this happened in the last couple of days, suggesting spectacular melting on the Pacific side of the Arctic:

So, what's going on?

Melting momentum: May 2017

Here's a quick blog post, which is mostly a copy of a comment I just wrote on the 2017 melting season thread on the Arctic Sea Ice Forum. For those who want to know more about what melting momentum means, read these blog posts from 2015 and 2016.

I've been in contact with Dr David Schröder from the University of Reading and he has confirmed (or rather his model) that this year (again) there is less melt pond formation than in years with low minimums. Below is a comparison of 2012, 2013, 2016 and this year:

Caveat: This is a model result, and so the distribution of melt ponds doesn't necessarily reflect reality.

As you can see, according to the model, there are even fewer melt ponds than last year. In fact, it looks very similar to 2013. Dr. Schröder wrote to me in an e-mail:

We predict the September Arctic sea ice extent 2017 to be slightly larger than last year: 5.0 +/- 0.5 mill. km2. In spite of the lowest Arctic ice volume in April, the May melt pond fraction in May is the second lowest of the last 10 years in our simulation with the sea ice model CICE. Anomaly figures with respect to 2006 to 2015 are shown for May 2017, 2016, 2012 (highest pond fraction) and 2013 (lowest pond fraction). Stronger melting and pond formation only occurred north of Canada and some parts of the Beaufort Sea. Otherwise the pond fraction is very similar to May 2013. Below average air temperatures (with respect to 2008 to 2015) and increased snow depth seem to have had a stronger impact in reducing pond formation than the thinner ice in increasing pond formation.

What's nice about this, is that it confirms our suspicions back in February when we discussed what could be the reason there was such a divergence between PIOMAS and CryoSat (as mentioned in the March PIOMAS update). The number one suspect was snow cover, mostly due to the relentless series of storms coming in from the Atlantic. Persisting snow on the ice is the best explanation for the fact that we haven't seen much melt ponding (ice turning blue on satellite images) so far, despite ideal weather conditions during the past two weeks.

As I wrote on the ASIF back in February:

This is pretty big, IMO, as it tells us something about snow depth on the sea ice which may have consequences for the state in which the ice pack enters the melting season.

Maybe we're in the process of getting the answer to that question. The last time there was such a divergence between PIOMAS and CryoSat was during the 2012/2013 winter. Remember, 2013 was cold and cyclonic, causing an unexpected rebound after 2012's spectacle. I don't think this year will be the same, if only for the fact that volume is at a record low because of a record mild winter, but 2017 could be 2016's rebound.

As always, everything depends on weather conditions, but also on sea surface temperatures, as I suspect this was a very important factor last year, causing the September minimum to end up as low as it did, despite a lack of melting momentum.

Back to the sabbatical now (this was too important not to mention).

2016 melting momentum, part 3

Melting momentum, it's what I call the absorption of heat and solar radiation during May and June that does not directly lead to melt and a reduction in ice cover, but rather comes into play during July and August (I had a more wordy explanation last year).

This is part 3 in the series.

As we saw last month, the melt pond fraction during May wasn't particularly high compared to previous years, and quite below that of 2012, effectively cancelling out the advantage that was built up on the extent charts. Back then it already looked highly unlikely that the 2012 record low minimum will be broken in September. This trend continued during June.

Dr David Schröder has been so kind as to send me the June melt pond fraction maps he uses for his SIPN 2016 Sea Ice Outlook prediction (blog post on June Report here). These results are based on the melt pond fraction simulation model developed by CPOM researchers at the University of Reading (more info). The comparison below shows melt pond anomalies for the years 2010, 2012, 2015 and 2016 compared to the average for the last 10 years:

Caveat: This is a model result, and so the distribution of melt ponds doesn't necessarily reflect reality.

The difference with 2010 and 2012 is clearly quite large. Just like last year May and June saw very little melting momentum being built up. Last year then caught up a bit because of one of the hottest Julys on record, eventually ending in third place with a September average of 4.63 million km2 (just like 2011, with 2007 and 2012 coming in at 4.30 and 3.63 million km2 respectively).

Dr. Schröder writes:

2016 melting momentum, part 1

Melting momentum, it's what I call the absorption of heat and solar radiation during May and June that does not directly lead to melt and a reduction in ice cover, but rather comes into play during July and August (I had a more wordy explanation last year).

As important as it seems to be for the final outcome of the melting season, it is one of those aspects of Arctic sea ice that has proven to be really difficult to measure. Observations based on satellite images have been developed in the recent past, but for some strange reason, this research didn't receive further funding.

I will discuss some indirect and experimental measurements further below, but start off with the best tool we have by far to get a feel for how much melting momentum is being built up during this crucial period in the melting season: the melt pond fraction simulation model developed by CPOM researchers at the University of Reading (more info).

Again this year, Dr David Schröder has been so kind as to send me the May melt pond fraction maps he uses for his SIPN 2016 Sea Ice Outlook prediction, showing melt pond anomalies for the years 2012, 2014, 2015 and 2016 compared to the average for the last 10 years:

Caveat: This is a model result, and so the distribution of melt ponds doesn't necessarily reflect reality.

This past May has been similar to last year's, but nowhere near May 2012. Here are two more maps that show the difference in melt pond fraction with May 2012 and 2015 (red = more melt ponds now, blue = less melt ponds now):

Beaufort quick update

It's been a week since I announced that the ice in the Beaufort Sea was going to come under early pressure. Here's a quick update on what has happened so far, how the forecast played out, and what the short-term conditions for this part of the Arctic will be.

As expected, the Beaufort Gyre kicked into action, big time, with winds causing large cracks in the ice pack, moving it westwards and away from the Alaskan and Canadian coasts. The massive polynyas that are left behind, get partially covered with a thin veneer of ice.

Here's an animation showing the difference between LANCE-MODIS satellite images on the first of the month and two weeks later:

Quite impressive, isn't it? As if someone threw a giant brick into it.

Here's an animation showing all days between April 1st and 14th (the file is somewhat large, apologies if it loads slowly):

2015 minimum overview, part 2

This is a continuation of Part 1, wherein I posted several graphs and maps depicting the 2015 minimum, and the weather conditions leading up to it (Tamino has a great blog post showing the long-term sea ice extent trends, all of them, not just the cherry-picked, meaningless one the GWPF selected to mislead).

Before jumping into the ice age and volume data that is (perhaps) most interesting, intriguing, but also incomplete, I want to refer to one more factor that - besides weather conditions and ocean heat flux - can play an important role in how a single melting season plays out: land snow cover.

Here are the monthly Northern Hemisphere snow cover anomaly graphs from the Rutger University Global Snow Lab during the melting season:

It's clear snow cover got pretty low during June and July. It's a bit of a chicken-or-the-egg kind of mutual influence thing, with an albedo feedback leading to warming over land, leading to increased snow melt, etc. which then starts to influence the Arctic and its sea ice as well. There's been ongoing speculation on this correlation between land snow cover and sea ice for years now, and my guess is that there's a there there, but as it isn't the only influence, it's hard to quantify it. Either way, it has to do with (global) warming, as attested by commenter Al Rodger's guest blog a few years ago: The untold drama of Northern snow cover.

And so we turn to multi-year ice. I'll repost this animation from a blog post I posted two weeks ago, showing how virtually all of the older, thicker multi-year ice on the Pacific side of the Arctic has melted out this melting season:

More on melt ponds

After you've read the blog post below, make sure to check out this web page by one of the co-authors of the Nature paper, and also this page with lots of other Arctic sea ice goodies.

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A really good paper has been published online a couple of days ago on Nature, called September Arctic sea-ice minimum predicted by spring melt-pond fraction. It's really good because it's interesting, short, and it confirms what I've been suspecting for a while now. And when a paper confirms what one is suspecting, it must be really good, right?

All joking aside, the paper by Schröder et al. presents evidence that melt ponds play a very important role at the start of the melting season, to the point that it can heavily influence the September minimum. The last two melting seasons actually proved to be a great lesson in this respect. 2012 had a really good* start to the melting season, so good that when bad weather showed up, it didn't really slow down sea ice loss, the trend lines just kept dropping (low sea ice volume also played a role, of course). The reverse was true in 2013: cold and cloudy weather during the first half of the melting season caused a lagged response during the short periods when the Sun and higher temps finally got to the ice.

What Schröder et al. did, was develop a melt pond model and incorporate it into the larger Los Alamos sea-ice modelcalled CICE. Here's what they came up with:

Decreasing Arctic albedo boosts global warming

A new paper in PNAS, called Observational determination of albedo caused by vanishing sea ice, reminds me of scientific work Peter Wadhams published a year and a half ago wherein he showed Arctic ice melt is 'like adding 20 years of CO2 emissions'. He based this assertion on calculations, as can be read in this BBC article from around that time.

This new paper by Pistone et al., however, is based on observations (as it says in the title) and similarly concludes that the "decrease in albedo is equivalent to roughly 25 percent of the average global warming currently occurring due to increased carbon dioxide levels"

I've taken this last quote from a livescience article. Here's more:

Warming from Arctic Sea Ice Melting
More Dramatic than Thought

Credit: Stefan Hendricks, Alfred Wegener Institute

Since as early as the 1960s, scientists have hypothesized that melting sea ice amplifies global warming by decreasing Arctic albedo. Researchers have since devised climate models to demonstrate this phenomenon but, until now, nobody had relied entirely on satellite data to confirm this effect through time. [See Stunning Photos of Earth's Vanishing Ice]

Now, scientists based at the University of California, San Diego have analyzed Arctic satellite data from 1979 to 2011, and have found that average Arctic albedo levels have decreased from 52 percent to 48 percent since 1979 — twice as much as previous studies based on models have suggested, the team reports today (Feb. 17) in the journal Proceedings of the National Academy of Sciences.

The amount of heat generated by this decrease in albedo is equivalent to roughly 25 percent of the average global warming currently occurring due to increased carbon dioxide levels, the team reports.

"Although more work is needed, a possible implication of this is that the amplifying feedback of Arctic sea ice retreat on global warming is larger than has been previously expected," study co-author Ian Eisenman told Live Science.

Previous models of Arctic albedo have suggested the reflectiveness of white cloud cover could potentially mitigate a portion of albedo loss due to melting ice; but these new observations show that cloud cover has had a negligible effect on overall Arctic reflectivity, the team says.

While Arctic sea ice will not likely return to 1979 values in the near future, the ice does change from year to year and might still experience some comeback this century, though the extent to which this might happen remains unclear, Eisenman said.

Read the rest here.

Here's another quote from the September 2012 BBC article mentioned above:

Arctic warming -> extreme weather debate

Andrew Freedman outdid himself on Climate Central with an excellent overview of the scientific debate on the link between Arctic sea ice loss and a wavy jet stream causing weird and extreme weather. Coincidentally (?) there's an "extreme kink" in it right now that just caused the warmest December temperature ever measured at any site on the Alaskan Arctic Ocean shoreline region.

Freedman wrote the piece following the publication in Nature of a new paper - with Jennifer Francis as co-author - that claims that rapid Arctic warming has an influence on extreme summer weather events. The last couple of years a lot of pioneering research is being done in this area, which in my view is one of the most exciting and important scientific corners currently around. Which explains why more and more experts are keeping an eye on developments.

Study Adds to Arctic Warming, Extreme Weather Debate

A new study for the first time found links between the rapid loss of snow and sea ice cover in the Arctic and a recent spate of exceptional extreme heat events in North America, Europe, and Asia. The study adds to the evidence showing that the free-fall in summer sea ice extent and even sharper decline in spring snow cover in the Northern Hemisphere is reverberating throughout the atmosphere, making extreme events more likely to occur.

A giant panda was playing with ice cubes in Chengdu, China to cool off from the summer heat in August 2011. Credit: Zhongjun Liu

The study, published Sunday in the journal Nature Climate Change, is the first to find correlations between rapid Arctic warming and extreme summer weather events, since previous research had focused on the links between Arctic warming and fall and winter weather patterns.

While the study adds to the body of evidence pointing to the outsized role the Arctic is playing in shaping weather patterns, it won't end the debate within the scientific community over whether and how what is happening in the Far North could be having such far-reaching impacts.

There is virtually no controversy among climate scientists and meteorologists that massive changes have occurred in the Arctic environment during the past three decades, and that those changes are largely due to manmade greenhouse gas emissions.

Since the 1980s, Arctic sea ice extent has dropped at a rate of about 8 percent per decade during September, which is when the sea ice cover reaches its annual minimum. A record minimum was set in 2012. For a size comparison, consider that the area of summer sea ice lost since the 1980s would cover about 40 percent of the continental U.S., the study said.

Spring snow cover extent loss during June has dropped even more precipitously than sea ice cover, the study found, at a rate of about 18 percent per decade since 1979.