RECORD ARCTIC SEA ICE MELT
THIS POST IS A CRITICAL REVIEW OF A PHYS.ORG ARTICLE [LINK] ABOUT ARCTIC SEA ICE MELT IN SEPTEMBER 2018
PART-1: WHAT THE ARTICLE SAYS
A snapshot of melting Arctic sea ice during the summer of 2018 by Cell Press: Arctic sea ice concentration and thickness on September 23 2018. Credit: Juhi Yadav
- As sea ice in the Arctic retreats further and melts faster every decade, scientists are racing to understand the vulnerabilities of one of the world’s most remote and unforgiving places. A study appearing July 29 in the journal Heliyon details the changes that occurred in the Arctic in September of 2018, a year when nearly 10 million kilometers of sea ice were lost over the course of the summer (do they mean 10 million square km?). Their findings give an overview at different timescales of how sea ice has receded over the 40 years of the satellite era and show how the summer’s extensive decline is linked to global atmospheric processes in the tropics.
- At the peak of its melting season, in July 2018, the Arctic was losing sea ice at a rate of 105,500 square kilometers per day—an area bigger than Iceland or the state of Kentucky,. „On the ground, I am sure it would have looked like an excellent summer month in the Arctic, in general, but over the past four decades, September sea-ice loss has accelerated to a rate of 12.8% per decade and 82,300 square kilometers per year ,“ says co-author Avinash Kumar, a senior scientist at the National Centre for Polar and Ocean Research (NCPOR) in India.
- The researchers followed the warm water currents of the Atlantic north to the Arctic Ocean and tracked the ice as it subsequently retreated through the Chukchi, East Siberian, Laptev, Kara, and Barents seas. Thanks to higher temporal resolution and greater satellite coverage than had previously been available, they could also measure the ice’s decline through variables such as its thickness, concentration, and volume in addition to its extent throughout the Arctic. This dramatic loss of sea ice culminated at the end of the boreal summer, when in September, the ice had been reduced to a mere third of its winter extent.
- Then, the team compared the decline to the previous four decades of data. „In the summer of 2018, the loss of sea ice was three times higher than the reported loss at the beginning of the satellite era,“ says Kumar. „Our study shows that both the minimum sea-ice extent and the warmest September records occurred in the last twelve years.“
- Every year, news pops up of a new record of high temperature or fastest loss of sea ice in the Arctic region, but in the global system, each portion of the planet receiving climate feedback will lead to changes in the other parts as well,“ Kumar says. „If the sea-ice decline continues at this pace, it can have a catastrophic impact by raising air temperatures and slowing down global ocean circulation.“ These global impacts are partly why he became interested in trying to decipher the mysteries of the polar regions as a doctoral student studying the coastal zone in India. Now, he works at NCPOR, whose scientific programs, he says, are „truly trans-hemispheric, cutting across from north to south.“
- The researchers also turned their attention to the atmosphere, where they were able to gain insight into the processes that contribute to the loss of Arctic sea ice. They found not only that September of 2018 was the third warmest on record, but that there was a temperature difference within the Arctic itself: the temperature of the air above the Arctic Ocean (~3.5°C) was slightly higher than that of the Arctic land (~2.8°C).
- Their findings provide further evidence that ocean warming around the globe has influenced the natural cycle of the wind and pressure patterns in the Arctic. El Niños, or warm phases in long-term temperature cycles stemming from tropical regions, have long been known to drive extreme weather events around the world and are occurring with greater frequency as the world warms. El Niño cycles in the equatorial Pacific Ocean can carry warm air and water from tropical circulations to the Arctic, spurring the sea ice to melt. As the ice retreats, it cascades the Arctic into a positive feedback loop known as Arctic amplification, whereby the reduced ice extent gives way to darker ocean waters that absorb more of the sun’s radiation. As it retains more heat, temperatures rise and more ice melts, causing the Arctic region to heat up faster—about four times so—than the rest of the world.
- „If the decline of sea ice continues to accelerate at a rate of 13% per decade in September, the Arctic is likely to be free of ice within the next three decades,“ Kumar says. And just as sea-ice retreat is largely the result of anthropogenic pressures from across the globe, its impacts will be felt worldwide: this work adds to the mounting body of evidence that changes in the Arctic sea ice could be detrimental to weather patterns spanning the globe. He says, „The changes taking place in the Arctic can lead to other changes in lower latitudes, such as extreme weather conditions. The world should be watching tropical countries like India, with our research center saddled close to the beaches of Goa, and trying to understand—even in a small way—more about climate change and the polar regions.“
PART-2: CRITICAL COMMENTARY
- The article says that over the 40 years of satellite data for Arctic sea ice (extent and volume) and 40 years of satellite data for the lower troposphere temperature above the Arctic ocean, we find that over this period the temperature above he Arctic Ocean has been rising and this rise is attributed to anthropogenic global warming (AGW) that is thought to be a creation of the fossil fuel emissions of humans and that it can therefore be moderated by reducing or eliminating the use of fossil fuels.
- At the same time, we find that over these 40 years, Arctic sea ice extent and volume have been declining.
- Based on this observed relationship between temperature and sea ice data, the article concludes that the evidence therefore shows that AGW warming has caused the decline in Arctic sea ice.
- This attribution is tested with detrended correlation analysis at an annual time scale in a related post on this site [LINK] . The need for detrended correlation arises from the creation of spurious correlations by shared trends and also because the time scale for the proposed causation must be specified in the correlation test. Spurious correlations in time series data not corrected for shared trends with detrended correlation analysis is demonstrated by Tyler Vigen in his book and also on his website [LINK] [LINK]
5. Tyler’s work implies that to establish a causation relationship between two time series the time scale of the causation must be specified, the two time series must be detrended, and a statistically significant detrended correlation between the two time series at the specified time scale must be shown.
6. Detrended correlation analysis at an annual time scale between the AGW temperature above the Arctic Ocean and sea ice volume measured with the PIOMAS procedure is shown in a related post [LINK] . The charts below show the findings of this analysis.
7. The first chart shows the sea ice volume for the study period 1979-2019 for each year 1979-2019 and each calendar month from January to September. The second chart shows the average rate of sea ice decline for each calendar month over the study period 1979-2019 – and it shows that the highest rate of decline is seen in July and the lowest rate of decline is found in April.
8. The results of correlation analysis is displayed in third chart. Correlations are shown in blue and detrended correlation in red. The hypothesis is that rising temperatures cause decline sea ice volume and that requires a statistically significant detrended negative correlation between temperature and sea ice volume. Here we see what appears to be strong correlations in the source data (blue line) from corr=-0.4 to corr=-0.6. However, the corresponding detrended correlation (red line) are close to zer and even positive. This means that the correlation seen in the blue line are spurious correlations that are creations of shared trends and not indicative of responsiveness at an annual time scale.
9. We conclude from this analysis as follows: The data do show declining Arctic sea ice volume during a period of rising temperature but without evidence for the assumed causation of sea ice decline by AGW and therefore without support for the claim that these changes are driven by AGW and that therefore they can be attenuated with climate action in the form of reducing or eliminating fossil fuel emissions.
10. A MORE DETAILED ANALYSIS IS PROVIDED IN A RELATED POST ON THIS SITE [LINK] . SIMILAR ANALYSIS FOR SEA ICE EXTENT AND AREA ARE PROVIDED IN YET ANOTHER RELATED POST ON THIS SITE [LINK] . No evidence is found that the observed decline in Arctic sea ice extent or volume is driven by the rising temperature of anthropogenic global warming above the Arctic Ocean.
— Thongchai Thailand