Posts Tagged ‘Sea Ice Extent’

Arctic Sea Ice Update: Spring 2016

March 6, 2016
Graph showing the extent of Arctic Sea Ice in millions of square kilometres. This  has been measured by satellites on almost every day since 1979. It looks as though the Sea Ice Maximum this year will be the lowest ever recorded.

Graph showing the extent of Arctic Sea Ice in millions of square kilometres. This has been measured by satellites on almost every day since 1979. It looks as though the Sea Ice Maximum this year will be the lowest ever recorded. Data courtesy of the US National Snow and Ice Data Centre. Click for a larger version of the graph.

While I have been venturing South and East, the Arctic regions have been a enjoying a mild end to their long winter.

One way to quantify this is to use satellite imagery to measure the extent (in millions of square kilometres) of the area of sea which contains at least 15% of Sea Ice. This figure is called Sea Ice Extent.

When the sea and air are cold, Sea Ice grows quickly and extends over a large area. So this relatively simple measurement provides a ‘proxy’ measure for the severity of the Arctic Winter.

Fortunately we have a continuous record since 1979 and the graph at the head of the page shows this years data in context.

Although the freeze is not quite (it usually ends around the Equinox on March 21st), it looks like the extent of Arctic Sea is the lowest it has been at this time of year – at least since 1979.

This is consistent with the long-term trend which has seen the Maximum Extent of Sea Ice shrink by approximately 40,000 square kilometres per year on average.

This is only half the long-term trend in the Minimum Extent of Sea Ice which occurs every September. This has been shrinking by approximately 83,000 square kilometres per year on average.

Using just a linear extrapolation, we would expect the entire Arctic ocean to be free of Sea Ice in September in just 60 years – by 2076. However there many reasons to expect this to happen much faster.

Personally, I expect see the Arctic ‘ice-free’ in summer in my lifetime, which I am anticipating will end in 2040 at the age of 80.

It is worth noting that the record low extent of the winter freeze is not necessarily an indicator that the summer melt will also reach a record low extent. The US National Snow and Ice Data Centre have an excellent discussion of these issues and many more here.

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P.S. Whew: All that and still I managed to avoid the use of the phrase minumum maximum!

Why do I punish myself?

January 13, 2014
An image from the GWPF Web SIte purporting to show that there was more sea in December 2013 than at any time in history. Can that really be true?

An image from the GWPF Web Site purporting to show that there was more sea-ice in December 2013 than at any time in history. Can that really be true? (Short Answer: No)

I ought to know better than to visit the web site of the Global Warming Policy Foundation. But I did: these things happen.

And there I saw the graph (above) which purports to show that there is currently (January 2014) more sea ice than there has ever been. The graph looks poorly plotted and it came with no explanation, but I thought that was a very strong claim so I just thought I would check if it was true.

So I popped over to NSIDC and downloaded the relevant data files for the Northern and Southern hemisphere sea-ice indices which record daily satellite measurements of sea-ice extent since 1978. The first graph below shows the data for the Northern and Southern hemisphere indices plotted together. This graph shows just the last few years of data.

Data from the US NSIDC showing Northern and Southern Hemisphere Sea Ice Extent since 2005.

Data from the US NSIDC showing Northern and Southern Hemisphere Sea Ice Extent since 2005. Click for a larger version

The graph below shows all the data taken nearly every day since 23 August 1978. On this graph I have also plotted the yearly averages and fitted a straight line to these to show the long-term trend.

Data from the US NSIDC showing Northern and Southern Hemisphere Sea Ice Extent since 2005.

Data from the US NSIDC showing Northern and Southern Hemisphere Sea Ice Extent since 1978. Click for a larger version.

This data highlights interesting differences between the two poles – these are discussed further on this excellent web page at NSIDC. You can see that both northern and southern hemispheres hold on average about the same amount of sea ice – around 12 million square kilometres (km2), but every year this grows and shrinks with the seasons.

  • In the southern hemisphere the sea ice falls to around 3 million kmin the antarctic summer and grows to around 18 million kmin the antarctic winter i.e. around 15 million kmof sea ice re-freezes every year.
  • In the northern hemisphere the sea ice falls to around 5 million kmin the arctic summer and grows to around 15 million kmin the arctic winter i.e. around 10 million kmof sea ice re-freezes every year.

So what of global sea ice? To find that I added the two data sets together and these are plotted below along with a yearly average. Because the extents of the antarctic and arctic freezes are different, globally the amount of sea-ice oscillates. However the annualised average global sea-ice extent is falling.

Data from US NSIDC showing global sea ice extent versus year. The trend is clearly downward by the difference between the two trends in the previous graphs.

Data from US NSIDC showing global sea ice extent versus year. The trend is downward by the difference between the two trends in the previous graphs.

And on the graph below I show how the extent of sea-ice in the northern and southern hemispheres are phased to yield a global maximum near the start of December.

Data from US NSIDC showing the northern hemisphere, southern hemisphere and global sea ice extent plotted versus the day of the year. The d

Data from US NSIDC showing the northern hemisphere, southern hemisphere and global sea ice extent plotted versus the day of the year. The data is same as that shown in the above two graphs but I have just ignored the ‘year’ label. It shows quite clearly the relative phasing of the sea-ice changes in the two hemispheres, and that December is the month in which global sea-ice extent is the largest.

So where does the data plotted by the GWPF come from? Well, I can’t tell for sure but I think it may simply be mislabelled. You can see that it is between 17 and 18 million kmwhereas the global sea-ice extent for December is around 25 million km2. So it might correspond to simply the Southern Hemisphere data which is indeed growing (slowly) and may well have reached its maximum value, but even that does not tie up precisely.

The GWPF do supply two links. The first one links to a web site called Real Science which just reproduces the graph without any analysis. The second links to the a data set which looks a bit like the Global Sea Ice Index but appears to be about 5 million kmlow. It too shows a trend which falls with time.

And where does the red line plotted on the graph come from? I have no idea.

So overall this is as wrong as wrong thingBut I have learned a little so the exercise has not been quite as useless as a useless thing.

Denial in Action

September 23, 2012
Interesting Map showing the different 'seas' within the Arctic Ocean. Source NSIDC

Interesting Map showing the different ‘seas’ within the Arctic Ocean. Source NSIDC

The collapse in the extent of the summer minimum of Arctic Sea Ice has been a shock to everyone, but in honesty, not really a surprise. But disappearance of three-quarters-of-a-million square kilometres of sea ice seemed to be such a dramatic change that I was sure that Climate Change ‘sceptics’ would be holding up their hands and saying simply ‘I was wrong’. So I headed over to the Sea Ice Update pages of Antony Watts ‘Watts Up’ site to witness their surrender.

But far from admitting that their world view was flawed, the ‘Climate Sceptics’ were responding in a manner which would be hilarious if it were not so tragic. The discussion is a classic example of a group unable to ‘distinguish the forest from the trees’. The discussion is focussed on individual facts (the trees) which are discussed in detail and critically examined. But they denounce anyone who raises the wider context of the facts (the forest) i.e. the only theory which predicted sea-ice melting. Indeed our concerns that this might happen are the very reason that the sea-ice data exists.

The page begins with a section noting that:

…there are some quite large Sea Surface Temperature Anomalies in the Arctic at present [up to 7 °C]. They appear to centered in four primary areas, the coasts of the Beaufort, Laptev and Kara Seas, as well as the middle of Baffin Bay. There are a multitude of potential explanations for these anomalies, let’s take them individually

We then get the individual potential explanations which I will summarise:

  1. Could be due to the low sea ice extent which means areas previously covered with ice are now exposed.
  2. Could be due to an ‘unusually strong storm’ which occurred early in August which could have broken up the ice cover.
  3. Could be Albedo Feedback – the replacement of reflective sea ice with dark ocean – likely to be a factor.
  4. Could be anthropogenically-warmed river discharges – quite likely a factor in some areas.
  5. Could be Northern Polar Lower Troposphere Anomalies – basically the air temperature has warmed over the decades, but enough for the trend to explain the sea surface temperature anomalies.
  6. Could be Tundra Vegetation Feedback – where the sea ice has retreated plants have begun to grow, changing surface albedo.

I have summarised these explanations but each one is discussed in detail. The discussions then cover other possible explanations:

  • Arctic Drilling
  • Undersea Volcanos
  • Soot from Chinese Coal Power Stations
  • The effect of the North Atlantic Oscillation – a persistent weather pattern with two distinct stable states.
  • Absorption of Energy from Geomagnetic Storms
  • Increased use of icebreakers and even tourist boats.
  • There has been no extra melting – just dispersal of sea ice into smaller pieces which are not counted as contiguous sea ice.

All these are discussed intelligently, helpfully and politely. It is an admirable example of a community of interested people discussing a topic. But when someone suggests:

There’s the increased release of anthropogenic greenhouse gases, such as CO2.

they are quickly told…

OK, you made a conjecture. Now, show a direct connection between Arctic ice melt and anthropogenic CO2, per the scientific method: testable, and using raw data. Otherwise, you have just expressed an opinion, nothing more.

In short – we don’t want to know about this.

In fact Climate models – our way of taking account of as many factors as we can think of – predicted long ago that Arctic warming would result from CO2 emissions. And Arctic warming can be reasonably expected to thin the ice sheet over the Arctic Ocean, which will then break up when there is a storm. All of the factors mentioned above may be proximate causes of the ice break up and enhanced sea-surface temperatures. But in fact the ultimate cause is in all probability the emission of greenhouse gases.

What we learn is that this group of well-meaning, interested and intelligent people simply rejected the most likely cause of this astonishing phenomenon. It caused me to wonder, if  there were any event which would cause these people – not perhaps to change their minds – but to perhaps shift their opinion slightly. To consider that perhaps all the world’s experts in Climate studies might just have a point worth considering?

Ice in the Antarctic

April 14, 2010
Before and After Pictures of the Larsen B Ice Shelf in Antarctica

Before and After Pictures of the Larsen B Ice Shelf in Antarctica

Two stories crossed my path this week both concerning ice in the antarctic, and taken together they form an interesting commentary on the drama, the challenges, and the context – of climate science.

NASA

The first story was a regular update from NASA’s Earth Observatory on the disappearance of the Larsen B ice shelf in 2002. I have made a composite picture (above) of the ice shelf before its collapse, and its absence after its collapse. There are articles describing:

The cause of the collapse? Well it was probably the melt ponds (visible in the left-hand satellite picture above as blue streaks) caused by an anomalously warm summer. The theory is outlined here. Taken together they form an interesting commentary on the drama of events in the antarctic.

The Register

The Register also had a story about scientists extracting Ice Cores in this area to see if there was anything anomalous about the Ice Shelf collapse. The Register story is simply a re-hash of a press release from Eureka – the press agency of the American Association for the Advancement of Science. I find it interesting to see just how little the author has bothered to change. I also note that he has failed to quote his primary source. At face value, it is an interesting commentary on the challenegs facing scientists trying to understand events in the antarctic – the work is just hard and everything breaks when it gets cold!

The context

Now The Register is not so much climate sceptical as climate cynical in a typical juvenile manner. And so they have to get in a few jibes about how really scientists don’t understand what is happening and how the Larsen Ice Shelf Collapse is anomalous. However, it is not actually that uncommon according to the NASA articles. And they have to throw in a confusing ‘factoid’ to make it seem that really there is no evidence for anthropogenic climate effects. In this case they throw in the fact that while Arctic sea ice cover is declining at 4% per decade, Antarctic sea ice cover is increasing at approximately 1% per decade. These facts arte presented like they are some way ‘equivalent’ and so cancel each other out on some kind of climate ‘factoid’ debate.

You can read about the facts here. Its a great page, full of information not amenable to soundbites. But the summary graph of the arctic and antarctic sea ice extent is given here:

Arctic and Antarctic Sea Ice Extent 1979 2009, Courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder

Arctic and Antarctic Sea Ice Extent 1979 2009, Courtesy of the National Snow and Ice Data Center, University of Colorado, Boulder

Now I have analysed a few graphs in my time and the red line looks to me to be barely above statistical significance. I have written asking for the data so I can establish an uncertainty on that slope.

Taken together these, different aspects of the ‘story’ illustrate concisely the challenging context in which scientists trying to understand events in the Antarctic have to work.


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