New charts - northern hemisphere Arctic sea ice maxima

A recent publication has highlighted the importance of the maximum extent of seasonal ice cover in the Arctic Ocean to the stability of the over all sea-ice system. So I have acquired data from NOAA of the daily sea ice extent since 1979, which I have used to find the maximum annual extent and the date (expressed as a Julian Day - so March 1, 2019 would be day 60, but March 1, 2020 would be day 61). These data sets will be studied in the usual manner, if appropriate. (I used the five-day trailing average, by the way).

The maximum sea-ice coverage has declined since 1979

The graph suggests that the maximum extent of ice coverage has declined more or less constantly over the observation period. There are a few ups and downs. In fact, something popped out at me. In the graph above, what do 1998, 2001, 2008, 2012, and 2020 have in common? They all represent years where sea ice extent increased - presumably due to cooling. They were also years with somewhat trying economic circumstances, at least for some people. Coincidence? Probably--but maybe it means there was an agricultural trigger to some of the economic crises of the past few decades.

There has been an idea that as global warming proceeds, the timing of certain important events will change, becoming either earlier or later. Investigating the above graph for a trend in the timing of the ice extent maximum each year tells me . . . nothing. If there is a trend, it is very weak.

Below we have the 2-d reconstructed state space portrait of the annual maxima sea ice extent, using the time-delay method with a 2-year lag. 

The state space reconstruction shows three regions of stability. The S1 and S2 correspond roughly to the major area of stability in the sea-ice minima phase space, which may actually be two separate such regions, one larger than the other. S3 corresponds with the most recent low-area sea-ice minima.

As with the sea-ice minima plots, there is not enough data to determine the long-term future of this system. It is possible we are in a declining phase of a century-scale cyclical system. Alternatively, we could be on a decline to zero. We may even be in a biased cycle, where the natural cycle is being influenced by global warming. The problem is that the data are not sufficient to tell us which is the correct interpretation.

Arctic sea ice minimum 2018

We are near the Arctic sea-ice minimum for 2018, which is projected to be 4.6 million square km

This gives us another point on our 2-d phase space projection. There is actually very little change from last year. I still only see two main areas of Lyapunov stability, although its possible there was a separate solution prior to the mid-1980s, when the system was confined to a much smaller region of phase space.

If the hypothesis of human activity on climate is correct, then we might interpret the first significant change as having happened around 1980, when the system expanded into a greater area of phase space. In colloquial terms, we would say that the variability of the system increased markedly.

Increased variability is potentially one of the markers of human influence on climate. If so, then the first irreversible change we see in our data occurred around 1980. The next one happened shortly after 2000 when the system migrated from one area of Lyapunov stability to another.

Dendritic fractures in river ice

We've had a pretty cold winter for this part of the world. Nothing like what you are having in Ontario, though. But still cold enough that I wish I hadn't forgone a winter coat this year.

This is the first time I have ever seen snow in Zhengzhou stay on the ground for more than a week. The canals froze, but that happens at least once every winter. They stayed frozen for longer than usual, until the warm spell that started just before the weekend.

Last weekend, crossing the bridge on Nongyedong Lu just east of Zhongzhou Lu, I saw these.

Cracking and refreezing. The dendritic pattern usually indicates a diffusive process, but am not sure how that translates here.

After the recent Arctic sea ice minimum . . .

. . . we have a new reconstructed state space diagram.

This year's minimum is 4.64 million sq km, which is a nice improvement from last year, and keeps the chart well within the lower area of Lyapunov stability proposed here about four years ago. With each passing year, my confidence that we have really entered an area of stability grows.

It is still unclear when the system will break out of its current area of stability, and what it's most likely behaviour will be (the two main contenders being a return toward the earlier area of stability at upper right, or a continuation towards the ice-free conditions forecast by so many. .

Ice under cloud

Yesterday's flight took me north from Toronto, over Hudson Bay and into the western part of the Northwest passage, then over Melville Island and on into the Arctic Ocean.

These are digital photos from a commercial flight, with some post processing to balance colours.

Looking down through clouds at ice floes in the western part of the NW Passage.

I'm not sure whether the larger agglomerations of ice are parts of the ice pack that haven't broken up entirely, or are part of the multi-year ice that has broken free from islands or ice shelves..

Sea ice seen through a couple of holes in the clouds.

In the Arctic Ocean, we seem to have flown over an area where the ice hasn't broken up at all. We can clearly see frozen leads in the ice.

Landslide in Alaska - aerial views

In the past two years there have been some spectacular avalanches in Alaska.

The first happened in Icy Bay, and caused a tsunami estimated to have been nearly 200 m high.

The second happened earlier this year in Glacier Bay, a little farther south, and seems to have missed the water, but left a large deposit on top of the ice.

Here are a couple of pictures of the second landslide, taken about two months ago as I flew over Alaska.

Arctic sea ice still hanging around

Another autumn, another sea ice minimum to add to the chart I have been posting yearly for awhile now. This year's minimum was about 4.1 million square km, among the lowest measurements on record.

Nevertheless, there still is not enough information for us to distinguish among several competing hypotheses.

1) The variation in sea ice is part of a dynamic natural cycle, which is currently in a lower area of Lyapunov stability, but which will at some point return to the higher area of stability (as it was prior to about 2003). There are alternatives to this hypothesis, such as the sea-ice system may naturally oscillate between two or more states, but this oscillation is being modified by anthropogenic effects.

If we are observing a natural cycle, and its duration is related to the time observed within the higher area of Lyapunov stability, then at some point the system will return to the area of stability occupied prior to 2003. The typical duration of natural climatic cycles is from a few years to decades. Given the length of time that the system occupied the higher Lyapunov-stable area, I would assume we are looking at a fairly long cycle length--meaning even in the best-case scenario (no anthropogenic effects) we would expect to remain in this state of lower sea-ice extent for at least another decade. A breakout, if it occurs will be towards the right first, before curving up toward the higher area of Lyapunov stability.

If anthropogenic effects are modifying the trajectory of the system, then we may still get an upward breakout, but it may be a short-lived one where the state does not reach the higher area of Lyapunov stability before falling back, either to the current Lyapunov-stable area, or possibly to a new, lower one. Even if, during the breakout, the system reaches the higher area of Lyapunov stability, it may remain there only a short time before returning to the present one or perhaps a lower one.

2) The variation in sea ice extent is in secular decline, likely driven by greenhouse gas emissions, but the dynamics of the natural system have temporarily arrested the decline in the current area of Lyapunov stability. In this case, we may expect the system to remain within this area of Lyapunov stability, before breaking out to the left and arcing downward.

Distinguishing between these differing hypotheses needs more time, but unfortunately we run the risk of an irreversible change occurring as we wait. Better would be to extend the record backwards by several decades, which can probably only be done by collecting near-surface sediment cores, and looking at their microfossils.

Coastal Alaska

Good weather when flying down the coast of Alaska, on the way to Vancouver from Beijing. My first photographic survey of the coastal glaciers there in about 20 years.

Glacier, trailing to the upper right.

Mount McKinley (Denali to Alaskans) in the distance.

Glacier feeding into a lake, with another at top.

Glaciers cascading into a fjord.

 

If this is the one I think it is, it has receded quite a lot in the last twenty years. Most of the water in the foreground was under glacial ice the last time I photographed it.
 

 

All of these were photographed digitally, and the colours were rebalanced afterwards. The original shots are too blue. The brownish shading on the left is a reflection from the edge of the window.

Arctic sea ice extent 2015

Arctic sea ice still appears to be trending downwards.

This chart is a little different over last year's, as TPTB have re-evaluated some past years' extent of sea ice, and found the previous estimates wanting. Almost every value has declined somewhat. The updated values have been added into the analyses below. I have no comment on the updates or the methodology, which is available here.

The question at issue is whether the change we are observing is a secular trend towards zero (in-line with global warming arguments) or part of a larger cycle, in which sea ice extent may eventually return to the heights of the late 1970s.

Many natural systems (and some unnatural ones) are characterized by multistability, whereby there are more than one equilibrium within a system for a given set of boundary conditions. Multistable systems show long periods of relative stability about an area of phase space, punctuated by brief, rapid shifts to alternative long-term behaviours.

The phase space portrait projected above into two dimensions has been interpreted as representing a system that has "switched" from one metastable mode of operation to another. The existence of different modes of operation is tied to the presence of both negative and positive feedbacks within the system. The interpretation is based on empirical data, not on models.

Unfortunately we don't have enough data to be confident of the interpretation. If we had a longer record, we might be able to infer multistability--but ice extent records prior to the advent of continuous satellite monitoring are difficult to compare with more recent records. Unless some proxy record is discovered, we will just have to wait.

Sea ice in the East Siberian Sea

Yesterday going almost over the pole . . .

The companion to this post.

Some multi-year ice. Looks like leads opened, later re-freezing, before the current pan formation. Some have had leads form and refreeze multiple times.

In any case, this is just a warm up before our annual posting on sea ice, at the end of next month.