Arctic Sea Ice

Northwest Passage as good as open

A little over six weeks have passed since I wrote the last blog post on the Northwest Passage (NWP): Still chock-full of ice. Since that post the NWP was hidden most of the time by clouds, no telling really what was going on down there. In the last couple of days I noticed on the sea ice concentration maps as put out by the University of Bremen that ice concentration in most of the NWP was very low. This has now been confirmed by satellite images:

I don't think it will be declared open officially yet. There is still some ice rubble here and there in Parry Strait and Lancaster Sound, and ice in the Beaufort Sea is still blocking McClure Strait for now. But the rubble will clear and the ice will pull back, making the NWP navigable for the fifth time in six years (previously in 2007, 2008, 2010 and 2011). With the Northern Sea Route almost open as well, we witness yet another summer in which both Arctic sea routes have opened up. This was a very rare occurence in the past, but has already become almost normal in current times.

ASI 2012 update 8: it shouldn't, but it does

During the melting season I'm writing (bi-)weekly updates on the current situation with regards to Arctic sea ice (ASI). Central to these updates are the daily IJIS sea ice extent (SIE) and Cryosphere Today sea ice area (SIA) numbers, which I compare to data from the 2005-2011 period (NSIDC has a good explanation of sea ice extent and area in their FAQ). I also look at other things like regional sea ice area, compactness, temperature and weather forecasts, anything that can be of particular interest.

Check out the Arctic Sea Ice Graphs website for
daily updated graphs, maps and live webcam images.

ATTENTION: There are still 3 days left to vote on the polls in the right hand bar.
One is for Cryosphere Today minimum daily sea ice area, the other for NSIDC minimum monthly sea ice extent (the one that is used for the SEARCH SIO projections). More info in this blog post.

July 28th 2012

I'm basically going to say the same thing as I did in the last ASI update: Weather patterns haven't been conducive to sea ice decrease, trend lines on graphs should be stalling, but they don't. As I've shown in yesterday's blog post comparing this year's weather patterns in June and July with previous record years, the decrease should have slowed down significantly like it did in 2010 and 2011, but it didn't. The 2012 SIE trend line shouldn't follow 2007 so closely, but it does. The 2012 SIA trend line shouldn't lead, but it does.

Now air and sea surface temperatures are higher than in previous years, but does that explain all of it? Personally, I don't think so. I think ice thickness is playing a big part in all of this. One of the conclusions I found most important last year, was that, yes, the weather is still dominant and determines whether a melting season will see a new minimum record or not, but only as much as ice thickness will allow it. There comes a point when large parts of the ice pack become so thin that it doesn't matter what the weather does. Sure, ideal conditions will cause a nosedive, but the train keeps chugging along, even when the weather isn't so great for melt, transport and compaction.

I believed I saw that in September 2011. I believe I'm seeing it now too,
4-6 weeks earlier. Maybe my eyes deceive me.

Sea Ice Extent (SIE)

In the last ASI update I was wondering whether the 2012 trend line
on the IJIS SIE graph would veer off to the right towards big staller 2010:

But it didn't. Especially in the last couple of days the 2012 trend line has decided to track new leader 2007, after following 2011, which had a brake put on its decline in mid-July. 2007 had a very strong first week in August, so it will be interesting to see whether 2012 can keep up or not.

The current difference between 2012 and other years (without the unrealistic last data point that gets revised upwards) is as follows:

Arctic atmosphere June-July 2012

In this exciting battle between Greenland and the Arctic sea ice (who gets the most media coverage?), it's now time for one of those boring comparisons that give the current melting season some more context. For that I have used the excellent maps on the daily mean composites page from NOAA's Earth Science Research Laboratory.

Let me start off with sea level pressure (SLP) from June 1st to July 15th, divided into three two-week periods. Since 2012 is still so low on SIE and SIA graphs, I figured it's best to compare it with other record years such as 2007, 2010 and 2011 (2008 became competitive towards the end of the melting season).

Tom Wagner of NASA explains

Hat-tip to Climate Denial Crock of the Week:

He's good!

Loss of Arctic sea ice '70% man-made'

Greenland has had its day in the Sun. Now it's back to the Arctic sea ice.

The Guardian has more for me to copypaste today:

Loss of Arctic sea ice '70% man-made'

Study finds only 30% of radical loss of summer sea ice is due to natural variability in Atlantic – and it will probably get worse

Since the 1970s, there has been a 40% decrease in the extent of summer sea ice. Photograph: AlaskaStock/Corbis

The radical decline in sea ice around the Arctic is at least 70% due to human-induced climate change, according to a new study, and may even be up to 95% down to humans – rather higher than scientists had previously thought.

The loss of ice around the Arctic has adverse effects on wildlife and also opens up new northern sea routes and opportunities to drill for oil and gas under the newly accessible sea bed.

The reduction has been accelerating since the 1990s and many scientists believe the Arctic may become ice-free in the summers later this century, possibly as early as the late 2020s.

"Since the 1970s, there's been a 40% decrease in the summer sea ice extent," said Jonny Day, a climate scientist at the National Centre for Atmospheric Science at the University of Reading, who led the latest study.

"We were trying to determine how much of this was due to natural variability and therefore imply what aspect is due to man-made climate change as well."

To test the ideas, Day carried out several computer-based simulations of how the climate around the Arctic might have fluctuated since 1979 without the input of greenhouse gases from human activity.

Unprecedented Greenland Ice Sheet Surface Melt

This just in from NASA (hat-tip Apocalypse4Real):

Satellites See Unprecedented Greenland Ice Sheet Surface Melt

July 24, 2012: For several days this month, Greenland's surface ice cover melted over a larger area than at any time in more than 30 years of satellite observations. Nearly the entire ice cover of Greenland, from its thin, low-lying coastal edges to its two-mile-thick center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

On average in the summer, about half of the surface of Greenland's ice sheet naturally melts. At high elevations, most of that melt water quickly refreezes in place. Near the coast, some of the melt water is retained by the ice sheet and the rest is lost to the ocean. But this year the extent of ice melting at or near the surface jumped dramatically. According to satellite data, an estimated 97 percent of the ice sheet surface thawed at some point in mid-July.

Extent of surface melt over Greenland’s ice sheet on July 8 (left) and July 12 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12.

Peeking through the clouds

When low-pressure areas take over the Arctic, they do two things: make the ice pack diverge and increase cloudiness. The diverging of the pack is hidden by the clouds, but we can sometimes see the holes in the ice pack through holes in the cloud cover on the LANCE-MODIS satellite images. We saw some early examples of that this year, ever since lows started to invade the central Arctic (for instance here and here), but it was and remained difficult to get an idea of the extent of holes in the ice pack. Until commenter Dr Tskoul came up with this tip:
MODIS Composites by Environment Canada.

Every Wednesday EC releases a 7 day MODIS satellite composite image, compiled to create a mosaic image of the Arctic Basin. They make a True-Colour Composite image as well as a False-Colour Composite image. I find the latter particularly interesting because it shows the holes best, as it highlights colour differences between sea ice and cloud. As a result, sea ice and snow appear light blue and clouds appear white (and purple over water).

This is the latest composite image (found in this directory):

CT SIA anomaly drops below 2 million km2

With a drop of 174,867 square km for July 17th reported by Cryosphere Today (run by the Polar Research Group at the University of Illonois at Urbana-Champaign), the 2012 sea ice area anomaly has dropped below 2 million square kilometres, compared to the 1979-2008 mean:

So what, one may ask. It happened before, right?
It did, as we can see on CT's Tale of the Tape:

It happened four times before, twice in 2007 and twice in 2011. Both record minimum years in the CT SIA data set had a first small dip a couple of weeks before the minimum, and a bigger one during the period of re-freeze:

First dip 2007: Aug. 19th - Aug. 23rd
Big dip 2007: Sep. 25th - Oct.29th (reaching the record anomaly of -2.635 million km2)

First dip 2011:Aug. 24th - Aug. 25th
Big dip 2011: Oct. 13th - Oct. 24th (reaching -2.224 million km2)

This year the negative anomaly has dipped below 2 million km2 on July 17th, more than a month earlier than the previous earliest record.

As we can see on the first image in this post, total CT sea ice area has also dropped below the 5 million km2 mark. This, of course, is also the earliest date for this to happen on record, as shown by this graph made by Jim Pettit (see his other graphs here):

Petermann calves again

Petermann Glacier has calved another large ice island, about half the size
of the calving of two years ago, which amounts to about two Manhattans.

This is what it looks like:

This second big calving (spotted this time by Arcticicelost80) is another spectacular event on Greenland this year, following retreats of the Jakobshavn Glacier and lowest reflectivity of the Greenland ice sheet on record (see blog post), leading to unprecedented flooding in the southwest of Greenland. This calving was expected to happen, as the rift in the glacier has been there for years (see this thorough explanation by glacier expert Mauri Pelto).

From the Icy Seas blog:

This morning Petermann Glacier lost another ice island of a size comparable to what it lost in 2010:

The break-off point has been visible for at least 8 years in MODIS imagery propagating at speeds of 1 km/year towards Nares Strait. The fracture also extended further across the floating ice sheet from the northern towards its southern side.

This event is still evolving, Trudy Wohleben of the Canadian Ice Service noticed it first (as in 2010) after reviewing MODIS imagery. Several people in several countries are monitoring and assessing the situation, but a first estimate of its size is 200 km^2 (3 Manhattans), I will revise this figure as soon as I got my hands on the raw data.

Read more here.

Two years ago Patrick Lockerby was the first to tell the world about the big calving that occurred at Petermann Glacier. The Arctic Sea Ice blog followed suit shortly afterwards. The whole event garnered a lot of attention, popularizing the island of Manhattan as an area measurement tool (square metre, square kilometre, Manhattan ;-) ). This second big calving in as many years doesn't come as a surprise, as attested by this article on the New York Times blog from August last year:

ASI 2012 update 7: steady as she goes

During the melting season I'm writing (bi-)weekly updates on the current situation with regards to Arctic sea ice (ASI). Central to these updates are the daily IJIS sea ice extent (SIE) and Cryosphere Today sea ice area (SIA) numbers, which I compare to data from the 2005-2011 period (NSIDC has a good explanation of sea ice extent and area in their FAQ). I also look at other things like regional sea ice area, compactness, temperature and weather forecasts, anything that can be of particular interest.

Check out the Arctic Sea Ice Graphs website for
daily updated graphs, maps and live webcam images.

* There are still two weeks left to vote on the polls in the right hand bar.
One is for Cryosphere Today minimum daily sea ice area, the other for NSIDC minimum monthly sea ice extent (the one that is used for the SEARCH SIO projections). More info in this blog post.

July 15th 2012

Two weeks have passed since the last ASI update. At the time the weather forecast for the Arctic showed things that pointed to a (possibly big) nosedive on sea ice extent and area charts. The forecast became even worse, showing a very big, very strong high-pressure area over the Beaufort Sea and low- pressure systems on the Siberian side of the Arctic. In other words, a hefty Dipole Anomaly, that we saw so much of in 2007.

But none of it came about. The weather forecast completely changed its tune and instead was showing a low-pressure area taking over things. Which did come about. So the nosedive didn't really live up to its weather forecast potential, and I was expecting a lull, a stalling, a levelling off of trends on graphs, but this hasn't really come about either! In the end nothing much has changed when it comes to the graphs in the past two weeks.

If the weather forecast had come about, 2012 would have undoubtedly taken a big lead, but as we say in Dutch: If my aunt had had a dick, she'd be my uncle! Instead, 2012 keeps steadily ploughing towards the minimum (two months from now), still battling it out with the big boys, apparently not much perturbed by atmospheric patterns that brought a stop to the 2010 and 2011 marches for melting season glory. Although that stop could still be coming about in the next week.

I hope I can shed some light on the how, why, and whence from here, but sometimes I feel as if all I've learned in the past two years has already turned obsolete.

Sea Ice Extent (SIE)

Right when I expected the lull to start showing up on the graphs, IJIS decided to go for a string of century breaks that kept it in the wake of 2011:

We can clearly see how 2010 levelled off when the weather switched at the beginning of the month. The same thing happened to 2011 when the weather switched halfway through the month. And maybe we are seeing the start of a similar situation for this year, now that the string of century breaks has been followed by two daily decreases of just 58 and 57K km2.

The current difference between 2012 and other years (without the unrealistic last data point that gets revised upwards) is as follows: