Ik zag onderstaand bericht op 33andrain. Het lijkt mij de moeite waard om te delen.
So I'll get straight down to it with my comments below each chart. This report with provide a comprehensive update on Arctic ice extent and temperatures, a short update on Greenland and I'll close with a snapshot on Antarctica. Remember that many links to these and other charts are listed in the introductory post to this thread on page 1. There is also a map there showing all the Arctic's regions and seas for general reference.
The 2019 minimum ice extent was almost certainly reached on September 18th with a slight recovery since then. 
The sea ice concentration shows how fragile the remaining ice is and perhaps approaching 100% concentration over half of the area and 50% to 70% over another third with the remainder (mostly around the periphery) well below 50%.
This shows that until early August, 2019 was matching or exceeding the ice loss achieved during the record low year in 2012. Fortunately, due to a colder period and favourable winds, the rate of decline slowed appreciably during the rest of August. A further more gradual decline resumed during early September until the minimum was set on September 18th. The recovery now seems to be underway (more on this later on). So, 2019 finished well above the 2012 minimum extent. There had been some speculation that this year would beat the record low extent set in 2012. Fortunately this was a false alarm and the Arctic cyclones in August were not as intense as suggested in several forecasts and did not take up the critical position close to the pole.
This puts 2019 into context. This chart shows the 4 lowest ice extent years since satellite monitoring started in 1979 and probably in much of the last millennium before then (for much more on this, please refer to my "historic ice" post on page 1 of this thread, link: https://www.33andrain.com/topic/1367-the-arctic-thread/?do=findComment&comment=90617). The minimum extents for 2007 and 2016 were very similar but 2019 just edged a fraction lower. The light grey area is the average for this decade, which is the worst decade on record and all these 4 years are well below even that average. The darker grey area is the average extent over the last 25 years and the dark grey line is the 1981 to 2010 30 year mean.
Overall this is very bad and worrying but not quite as bad as seemed possible 2 months ago.
This table puts it into figures. Given that it's difficult to obtain an exact measurement, the NSIDC have actually ranked 2019 as 2nd equal with 2016 and 2007. We can see that the minimum extent usually occurs around 2nd or 3rd week in September depending on surface temperatures and wind strength and direction.
We can glean a lot of information from this chart which shows the ice extent through most of the year from the maximums around March to the minimums from 1980 to date. If we refer to the far right columns and the bottom 4 rows, these give the maximum and minimum volumes average over each decade. The minimum extent this decade is averaging around 440,000 sq km but it was nearly 700,000 sq km in the 1980s!
This chart shows the average ice thickness. There is very little left with 4m or more and much of the Canadian Arctic has an average thickness of 2m to 3m (the orange shade). The area from the pole towards northern Russia and north western Siberia has a thickness of nearer 1m or even less and this has been thinning steadily during most melt seasons this decade and is now getting worryingly thin. We need a rapid re-freeze which depends on a number of factors. Now that we are past the equinox, the strength of the sun is much less and declines rapidly. Land surface temperatures and sea surface temperatures are critical. Wind speed and direction can be very important. An early more powerful Atlantic jet stream can push warmer air and waters right up to the fringes of the main ice sheet and greatly impinge upon re-freezing. A weaker or more southerly jet can allow lower surface temps to stagnate. A rapid late melt, leaves a lot of fresher (low salinity) water near the surface which can refreeze much more quickly.
We have become used to seeing long periods with widespread Arctic region surface temp well above normal. This chart shows the anomalies for the last 30 days and compared to several recent early Falls and to much of the 2019 summer (particularly through July) these values are not too bad!
This chart shows the trend for the next 7 days compared to right now (not the actual forecast temps which are higher next week than they are now ) taking account of the sharp declining mean temp at this time of year. Most area will see the expected cooling trend. This is strongest near to the pole and that is good news.
Moving on to sea surface temperatures we can see that a wide area around, just beyond and also under the main ice sheet (and within the waters with more than 15% ice concentrations) with temps below -1.5c (purple). Although normal sea water usually starts to freeze at below -2c to -2.5c, the very low salinity means that freezing can commence at temps below -0.5c and certainly below -1.5c. So the area (darker blue) of 0c to -1.5c is important and, given the right conditions, can refreeze rapidly during the next few weeks up to mid/late October. A rapid early refreeze will be really important later in the Fall and can help to off set warmer incursions. For more on the Arctic Ocean salinity this is an excellent link: https://nsidc.org/cryosphere/seaice/characteristics/brine_salinity.html
This looks pretty gruesome at first sight but I've become used to these charts with the very high anomalies ever since the super El Nino in 2015 allowed long periods of Atlantic warm waters and higher surface temps to push well into the main Arctic basin. The high SST anomalies are a legacy of that event. They have only gradually subsided during the last 3-4 years and the extreme Arctic warmth earlier this summer did nothing to help! Beyond the periphery of the ice cap and the area of 15%+ ice concentrations and above the 0c SST temp contour, the anomalies rise really sharply. There are wide areas with +ve anomalies around 4c and some above that. That curious olive patch (over +8c anomaly) just west of Svalbard used to puzzle me as it has been there for several years but I've read that it's caused by thermals and subterranean volcanic activity. It is on the northern limits of the mid Atlantic ridge. There are a number of Arctic volcanoes and when I have time, I'll do a specialist post on them. There are several other even smaller olive patches which are all above warm thermals. There is a narrow area of -ve anomalies hugging the south-east Greenland coast and also slightly -ve temps closer to Scandinavia. This is one bit of good news. In recent winters that part of the Arctic has sometimes remained ice free throughout the winter - that includes the Barents Sea and sometimes the southern Kara Sea. Actual temps are still 4c to 6c but these tend to fall quite quickly during October and November and a good start really helps.
I show the same chart for 2018 for comparison. Very little difference although Baffin Bay (west of Greenland) was somewhat colder.
Greenland:
Following on from two years with lower net melt rates and higher summer snowfall in 2017 and particularly in 2018, 2019 has seen a close to record Greenland net ice loss and very little summer snowfall. The early part of this summer saw persistently high surface temperatures in Greenland, sometimes 15c-20c above average with many spots even in the higher plateau regions seeing temps above freezing for short periods (almost unheard of even in recent warm years). This resulted in near record levels of melting. Fortunately Greenland had a very cold spell from quite early in August that brought much of the melting to an abrupt halt. There is very little melting beyond mid September and snowfall tends to increase so that there is usually a net accumulation of snow and ice from now on. I shall do a longer Greenland post before the end of this year.
Antarctica:
Well there is some better news. Antarctica usually sees it maximum sea ice extent in early October.
Unlike the Arctic, sea ice in Antarctica has often approached its longer term mean in recent years. Until early August, Antarctica saw persistently below average ice build up and this was widely reported. There has been a pretty steady recovery since then with just a slight blip two weeks ago. The ice extent is now not far off the long term mean and the recent mostly colder than average temps in much of that region seems likely to continue for the next couple of weeks (or longer) and we may yet see ice extent ending up slightly above normal! I shall do a much more comprehensive post on Antarctica when I have time.
So, overall, the Arctic and Greenland ice news is extremely worrying and fingers crossed now for a rapid and early refreeze season. https://www.33andrain.com/topic/1367-the-arctic-thread/page/4/#comments