Arctic Sea Ice

PIOMAS September 2019

Apologies for this late update, but at least it will give me the opportunity to give my opinion/analysis of how this melting season has evolved, now that the minimum is just around the corner.

It also gives me the opportunity to announce that the Arctic Sea Ice Forum recently passed the 100 million pageview mark. This year already has the most pageviews since the ASIF's inception in 2013, and this month - only halfway through - already attracted more pageviews than any other month so far. My gratitude goes out to everyone who contributes with images, animations, analysis, speculation and heaps and heaps of information, all of them needed to help people become conscious of the severity of the situation human civilisation is in.

On to 1 billion pageviews!

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Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center:

Despite a massive amount of melting momentum and an advantageous thickness distribution, volume loss during August 2019 was below average (2301 vs 2559 km3 for the 2007-2018 period). Of course, being record low makes it harder to melt a lot of ice, but since 2007, only two years - 2013 and 2017 - managed to lose less volume than 2019 during August. This means that this year is no longer lowest on record, with 2012 breezing past and going 238 km3 lower. 2016, though profiting from the most extreme August weather conditions in the era of the New Abnormal, is still 521 km3 behind.

Here's how the differences with previous years have evolved from last month:

Wipneus' version of the PIOMAS graph shows that this year is the only one capable of staying somewhat close to 2012:

PIOMAS July 2019

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center:

To quote Céline Dijon*: This is getting serious.

With a total drop of 7066 km3 for June 2019, this was only the second time - after 2012 - that the 7000 km3-mark had been breached. It was just enough to squeeze past 2017 and take the lead in the rankings, while leaving all other years - except for 2012 - in the dust. For instance, the difference with 2008 has grown to 5395 km3, which amounts to a decrease of 30% in just a little over 10 years. The difference with 2016 (member of the 'second lowest minimum' triumvirate, together with 2007 and 2011) went from 208 to 1384 km3. But 2012 is now hot on 2019's tail, only 248 km3 behind, while 2017 is still second with just 108 km3 more volume than 2019 (the difference was 2460 km3 in 2017's favour at the end of January).

Here's how the differences with previous years have evolved from last month:

Wipneus' version of the PIOMAS graph clearly shows how 2019 (red line) and 2012 (purple line) have started to move away from the other trend lines:

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).

PIOMAS June 2017

Another month has passed and so here is the updated Arctic sea ice volume graph as calculated by the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) at the Polar Science Center:

Finally some good news, relatively speaking. The cold that crept over the Arctic during the last week of April, lingered for two more weeks into May, causing volume loss during that first half to be third lowest since 2007. But then the weather flipped, causing volume loss to pick up speed again and ending third (behind 2010 and 2012) for the latter half of May. Overall volume loss was just below the average since 2007.

And so the gap with number two has now become somewhat smaller. At the end of last month 2017 was 1595 km3 lower than runner-up 2011. In the meantime 2016 has become the runner-up, 1211 km3 behind 2017 at the end of May. The difference with 2012 has also been slashed by almost 1000 km3.

Here's how the differences with previous years have evolved from last month:

Wipneus' version of the PIOMAS sea ice volume graph clearly shows that the gap has become smaller, but 2017 is still well below all other years:

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:

ASI 2016 update 3: crunch time

During the melting season I'm writing (bi-)weekly updates on the current situation with regards to Arctic sea ice (ASI). Because of issues with data based on the SSMIS sensor aboard DMSP satellites, I mainly focus on higher-resolution AMSR2 data from the Japan Aerospace Exploration Agency (JAXA), as reported on the Arctic Data archive System website. I also look at other things like regional sea ice area, compactness, temperature and weather forecasts, anything of particular interest.

The animation on the right consists of NSIDC
sea ice concentration maps, one for each ASI update.

Check out the Arctic Sea Ice Graphs website (ASIG)
for daily updated graphs, maps, live webcam images, and
the Arctic Sea Ice Forum (ASIF) for detailed discussions.

June 29th 2016

The run-up to this melting season was really special, with an unprecedentedly warm winter season and early opening of the Beaufort Sea. Sea ice extent and area numbers went extremely low for the time of year, and sea ice volume reached the depths it was at before the 2013-2015 post-record rebound. But events in the Arctic don't behave like a straight arrow. Not in the short term, at least.

Weather conditions switched around the start of this month (see previous update) and prevented a large-scale soaking up of solar radiation through leads and melt ponds that would've increased the chances of a new record low September minimum even more. The lack of melting momentum has in fact decreased the chances to the point that I'd bet against it. If you want more details, read these two posts, or this blog post by Chris Reynolds that is hot off the press.

Mind you, this is not a melting season like 2013 or 2014 where persistent cloudiness and low temperatures caused relatively high September minimums (compared to top 3 years like 2007, 2011 and 2012, of course; they were well below the long-term average). 2016 still has many aspects going for it, like all that open water in the Beaufort Sea, low volume and snow cover that vanished at record speed. But it will take more to beat 2012, or 2007 and 2011 for that matter.

So, that's the question I will focus on in weeks to come: Can 2016 still make the top 3?

2016 melting momentum, part 2

Happy Solstice, everyone!

Credit: NASA/Kathryn Hansen

The previous post on melting momentum was running long, so here's an addition dealing with compactness, the final piece of information we have to assess the amount of melting momentum. Just before the start of July, the month of big melt. First, a couple of paragraphs to explain what compactness is and what it can tell us.

Not only melt ponds, but also open water between ice floes can absorb solar radiation, heating up the water, and then speeding up the melt process. We can get an idea of how compact an ice pack is by dividing sea ice area numbers (SIA) with sea ice extent numbers (SIE), the products of two different ways of measuring total sea ice cover.

The idea is simple, really. The Arctic is divided into grid cells, and each grid cell has a certain sea ice concentration. On the right there's an example of one such grid cell, with white representing ice and blue representing open water/melt ponds. This grid cell measures 10 x 10 km, and thus has a total area of 100 km2. Sea ice concentration is 80% in this grid cell, which means that 80 km2 is covered with ice. This is the number that represents sea ice area.

However, for sea ice extent there's a so-called threshold of 15%, meaning that if there's 15% of sea ice concentration or more, the entire grid cell is considered ice-covered. In other words sea ice extent for this particular grid cell is 100 km2. The reason for this different way of assessing total ice cover is to reduce the influence of melt ponds, that can fool satellite sensors into 'thinking' they're seeing open water.

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):