Antarctic Sea Ice Claims Don’t Stand Up To Scrutiny
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By Paul Homewood
From Yahoo:
A few days ago, the US National Snow and Ice Data Center announced that the Antarctic sea ice contracted to just 883,015 sq. miles, which is the smallest on record.
Experts assert that, if changes are not made to pollution and our fossil fuel industry, a number of species will be threatened as sea levels (and temperatures) continue to rise.
The Antarctic ice sheet goes through a cycle of expansion and contraction every year. Ultimately, the ice that exists around the continent melts during the southern hemisphere’s summer, which occurs towards the end of February, and expands again when autumn sets in.
However, that melting is increasing dramatically.
This week, the US National Snow and Ice Data Center (NSIDC) announced that the sea ice contracted to just 883,015 sq. miles (2.28m sq. km). The announcement came on February 13, and these numbers mean that the ice is now at the smallest extent on record, reaching just a little smaller than the previous low of 884,173 sq. miles, which was recorded February 27, 1997.
NSIDC director Mark Serreze asserts that we will need to wait for measurements in the coming days before officially confirming this new all-time low; however, he is not optimistic. “Unless something funny happens, we’re looking at a record minimum in Antarctica,” Serreze told Reuters.
Antarctic sea ice extent has been running below average for the last few months, and unsurprisingly the usual suspects have been jumping up and down and blaming it on global warming.
This despite the fact that Antarctic sea ice extent has been expanding in recent years, something that junk scientists, like Jim Hansen, have been trying to blame on, yes you’ve guessed it, global warming.
NSIDC’s propagandist in chief, Mark Serreze, is quite clear:
Climate change skeptics have often pointed to the tendency of the Antarctic ice sheet to expand as evidence against global warming. But with world average temperatures hitting an all time high in 2016, the impact of climate change on planet Earth is getting more pronounced and harder to deny. “We’ve always thought of the Antarctic as the sleeping elephant starting to stir,” Serreze stated; “Well, maybe it’s starting to stir now.”
He should know, since NSIDC, the organisation he is in charge of, has already reported, the sharp drop in sea ice since September has been due to changing wind wind patterns. This is linked to the Southern Annular Mode turning negative, allowing winds to penetrate from the north, both lifting temperatures and at the same time pushing sea ice towards the coast. (See here)
This is a perfectly natural phenomenon. We also know that sea ice in the Antarctic has fluctuated wildly, both up and down during the 20thC, and there is no reason to suppose that this time is any different.
However, there is another side to this story. Just how accurate are the numbers we are being fed with by NSIDC?
According to them, they have been using a new satellite instrument since April 2016.
Cryosphere Today, who usually provide sea ice data as well, also report that the satellite data they have received since last April is spurious, so there is no cross check with NSIDC.
NSIDC have become so politicised over the years that only a fool would trust the numbers they are putting out. And with something like sea ice , it is very easy to fudge the figures.
Which brings us onto the next point – margins of error.
As the Yahoo report points out, the extent this year is only 1158 sq miles less than recorded in 1997, just 0.1% less.
NSIDC do not publish error margins in their data archive, but even they admit that they can be huge, particularly in summer when ice concentration is low:
6.1 Accuracy and Precision
The accuracy of Arctic sea ice concentration at a grid cell in the source data is usually cited as within +/- 5 percent of the actual sea ice concentration in winter, and +/- 15 percent during the summer when melt ponds are present on the sea ice (GSFC Confidence Level), but some comparisons with operational charts report much larger differences (Agnew 2003, Partington et al 2003). Accuracy tends to be best within the consolidated ice pack where the sea ice is relatively thick (greater than 20 cm) and ice concentration is high. Accuracy decreases as the proportion of thin ice increases (Cavalieri 1995).
The accuracy of the median sea ice extent edge position for Sea Ice Index products has not been rigorously assessed. It would be difficult to do so, because ice edge is not a well-defined parameter. For our purposes, it is where source data grid cells transition from greater than 15 percent to less than 15 percent concentration. Operational services usually speak of a marginal ice zone of varying width over which concentration transitions from more than 90 percent to 0 percent. Spot checks of the sea ice edge position using a 15 percent concentration cutoff against NIC ice charts show that when there is a broad, diffuse ice edge, the NRTSI and GSFC products sometimes do not detect sea ice where the concentration can be as high as 60 percent (Fetterer 2003 poster). When the sea ice edge is more compact, the 15 percent concentration cutoff reflects its location fairly well (Fetterer 2002).
Defining the ice edge in SSM/I data using the 15 percent concentration contour has been common practice since the publication, in 1991, of a study that compared SSM/I ice concentration data from the NASA Team algorithm with coincident data from higher resolution airborne imagery. That study used remote sensing data acquired in March 1988 and found that aircraft-determined ice-edge positions matched the SSM/I 15 percent ice concentration contour (Cavalieri et al. 1991).
Ice concentration from low-resolution passive microwave data is not highly accurate; and for this reason, it is best not to use Sea Ice Index ice concentration images alone, out of temporal context, especially those from a single day. Ice extent images are more reliable, because the difference in emissivity between open water and sea ice, even at low concentrations, is great (Comiso and Kwok 1996). Still, the instrument’s low resolution (see Table 5) means that the ice edge, whether it is a compact or diffuse marginal ice zone, will not be represented well. For example, the daily 25 km SII extent product for 08 September 2011 is shown in Figure 21 along with the 4 km Multisensor Analyzed Sea Ice Extent (MASIE) product from the same day. MASIE resolves the ice edge with greater precision and accuracy, but it is not a long and consistently processed record. The Sea Ice Index daily product does a reasonable job, but it is evident why we place higher confidence in monthly than in daily products. Many errors due to missing data and transient weather effects are averaged out when we average daily data over a month.
To claim a record low based on a difference of 0.1% is clearly statistically nonsense. Worse than that, it is dishonest.
No serious scientist would dream of making such a claim, but this is NSIDC we are talking about.
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February 22, 2017 at 08:57PM
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