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By Javier
In sharp contrast with previous decades, the past 10 years have seen no change in Northern Hemisphere average sea ice extent, according to MASIE (may-zee, Multi-sensor Analyzed Sea Ice Extent) database from the National Sea & Ice Data Center (NSIDC; see figure 1).
Figure 1. MASIE sea-ice extent data for the Northern Hemisphere showing essentially no trend for Arctic sea-ice for the past 11 years.
Based on fundamental climate observations and research it has been proposed by several scientists that the Arctic might have entered a new regime with its most conspicuous consequence a reduction or even inversion of recent Arctic sea ice trends. So far, the data appears to support their interpretation. They are Miles et al. 2014, Wyatt & Curry 2014, and Årthun et al. 2017 (references in the appendix).
Last October I presented some of the evidence at WUWT here.
Despite the complete failure of every Arctic ice-free prediction so far, and the research and evidence that the Arctic is no longer melting as in past decades, some climate alarmists are rabidly attacking this interpretation and those that hold it, including me. See the “Open Mind” post: Extreme Cherry Ice.
MASIE is a relatively new (November 2010) and improved dataset on sea-ice extent for the Northern Hemisphere with very good sea-ice boundary resolution. Sea-ice extent is the preferred measurement by NSIDC to study melting, since surface melting is known to cause sea-ice area measurements to underestimate the sea-ice surface. However, sea-ice extent is rapidly falling out of favor among sea-ice alarmists as an Arctic gauge, replaced by sea-ice volume that has the disadvantage of being modeled, but the advantage that it shows continuous decline, as the models include a temperature factor. Apparently, alarmists believe that Arctic sea-ice is transforming from a pancake into a crepe of the same size.
MASIE starts in 2006. I have determined the start and end dates of the melt season from 2006-2017 (11 complete years; see appendix). The data is presented in table 1.
Table 1. Start day defined as yearly maximum extent day (7-day smoothed). End day defined as yearly minimum extent day. Length is the difference between both in number of days. Extent change is the difference between maximum and minimun sea-ice extent.
The average start for the melt season was on day 68 (March 9 in common years). For the past 12 years there has been a trend towards an earlier start of the melt season, with 2015, and 2016 starting on day 59 (February 28). The trend is very pronounced at –9 days/decade (see figure 2). Stroeve et al. 2014 report a similar trend for 1979-2013 of –2 days/decade. If anything, the trend appears to have accentuated recently. In 2017 the melt season started on day 63 (March 4) as determined by this methodology, right on the trend.
Figure 2. Start of the melt season for the past 12 years showing a pronounced trend towards an earlier start of the melt season.
The average end for the melt season was on day 262 (September 19 in common years). For the past 11 years there has been a trend towards an earlier end of the melt season, with 2016 (leap year) ending on day 253 (September 9). The trend is very pronounced at –11 days/decade (see figure 3). Stroeve et al. 2014 report an opposite trend for 1979-2013 of +3 days/decade. There is a huge inversion of 2 weeks/decade in this trend. According to the trend and methodology, the 2017 melt season is projected to end on day 255 (September 12) ± 1 week.
Figure 3. End of the melt season for the past 11 years showing a pronounced trend towards an earlier end of the melt season.
The observed trends are not sustainable (or the melt period would eventually shift seasons) and probably form part of the observed Arctic regime shift. One possible explanation is that for the past decade winters have become warmer in the Arctic, while summers have become cooler. A good example is this year situation (see figure 4).
Figure 4. Daily mean temperature north of the 80th northern parallel, as a function of the day of year. Source DMI. The average melt season start and end days have been added.
The average melt season length, defined as the number of days from start to end of melt, is 193 days (52.5% of the year, winter is 4 days shorter than summer). For the past 11 years the melt season length has shown a non-significant decrease of –2 days/decade (see figure 5). This contrasts with Stroeve et al. 2014 who report a trend for 1979-2013 of +5 days/decade in melt season length. The evidence does not support the touted increase in melt season length for the past decade. According to the trend, the 2017 melt season is projected to last 192 ± 6 days.
Figure 5. Melt season length for the past 11 years showing no clear trend.
The average extent loss from start to end of the melt season is 10.6 million sq. km. For the past 11 years the extent loss has shown a non-significant increase of 0.65 million sq. km/decade (see figure 6). This trend is dependent on the very low value of the 2006 melt season loss, and shows no increase in surface lost during the melt season from 2007. 2017 started its melt season with a very low value of sea ice extent (14.7 million sq. km), almost as low as 2006 (14.6), and has seen below normal melting so far, so it is likely to end with one of the lowest sea-ice extent losses of the entire series.
Figure 6. Change in extent (sea-ice loss) from start to end day of the melt season for the past 11 years showing no clear trend.
The average sea-ice extent change during the melt season was plotted against the length of the melt season (see figure 7). No significant relation was found as the trend depends fully on two outliers, the very low melting of 2006 and the very high melting of 2012. It is clear that melt season length is not the main determinant of sea-ice extent decrease during the melt season.
Figure 7. Change in extent (sea-ice loss) during the melt season versus the length of the melt season for the past 11 years. No significant correlation is found.
It is important to notice that the analyzed period 2006-2017 includes 7 of the 10 hottest years recorded according to NOAA/NCEI, as reported by Climate Central (see figure 8). 2017 is trending to finish in 2nd-3rd place. The warmest decade in over a century, according to this database, coincides with a decade when no Arctic sea-ice melting has taken place. This demonstrates that global average surface temperatures cannot be the driving force behind Arctic melting, and regional ocean surface temperatures are likely to be more important.
Figure 8. The period analyzed, 2006-2017, includes most of the warmest years ever recorded, and can therefore be considered the warmest decade ever registered. The lack of ice melting demonstrates that global temperatures do not drive Arctic sea-ice melting.
In conclusion, the evidence indicates that for the past 10 years:
1. There has not been any significant Arctic sea-ice melting.
2. Both the melt season start and end have been taking place earlier.
3. The melt season length has not increased.
4. Sea-ice loss during the melt season has not increased.
5. Sea-ice loss during the melt season is not determined by season length or by the average global surface temperature, as claimed by the IPCC.
There is a stark difference between the results from the past 10 years and from earlier decades. This difference suggests a shift in the Arctic ice regime as proposed by Wyatt & Curry 2014 and Miles et al. 2014. The expectation from these authors and from Årthun et al. 2017 is that for the next decade(s) no significant Arctic sea-ice melting should be expected, and a significant increase in Arctic sea-ice is possible.
Appendix.
The MASIE database was downloaded from:
ftp://sidads.colorado.edu/DATASETS/NOAA/G02186/masie_4km_allyears_extent_sqkm.csv
on August 8, 2017.
The Northern Hemisphere data was smoothed with a 7-day centered moving average to reduce daily variability.
Data was plotted with Excel.
Daily polar temperature graph was obtained from the Danish Meteorological Institute at:
Bibliography:
Årthun, M., et al. 2017. “Skillful prediction of northern climate provided by the ocean.” Nature Communications, 8, ncomms15875.
Miles, M.W., et al. 2014. “A signal of persistent Atlantic multidecadal variability in Arctic sea ice.” Geophys. Res. Lett., 41, 463–469.
Stroeve, J.C., et al. 2014. “Changes in Arctic melt season and implications for sea ice loss.” Geophysical Research Letters, 41(4), 1216-1225.http://onlinelibrary.wiley.com/doi/10.1002/2013GL058951/full
Wyatt, M.G., and J.A. Curry. 2014. “Role for Eurasian Arctic shelf sea ice in a secularly varying hemispheric climate signal during the 20th century.” Climate dynamics 42.9-10: 2763-2782.http://cdn.cnsnews.com/documents/Curry,%20Wyatt%20paper.pdf