The Melting Arctic
Arctic Sea Ice Conditions
In recent decades, sea ice in the Arctic Ocean has been melting faster than it re-freezes in winter. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report states that greenhouse gas forcing is predominantly responsible for the decline in Arctic sea ice extent.
A 2007 study found the decline to be "faster than forecasted" by model simulations. A 2011 study suggested that this could be reconciled by internal variability enhancing the greenhouse gas-forced sea ice decline over the last few decades. A 2012 study with a newer set of simulations also projected rates of retreat which were somewhat less than that actually observed.
The IPCC Fifth Assessment Report concluded, with high confidence, that sea ice will continue to decrease in extent, and that there is robust evidence for the downward trend in Arctic summer sea ice extent since 1979. It has been established that the region is at its warmest for at least 4,000 years and the Arctic-wide melt season has lengthened at a rate of 5 days per decade (from 1979 to 2013), dominated by a later autumn freeze-up. Sea ice changes have been identified as a mechanism for polar amplification.
Satellite observations show Arctic summer sea ice minimum extent in 2018 and 2019 was no lower than the extent measured in 2007.
The Arctic Ocean is the mass of water positioned approximately above latitude 65° N. Arctic Sea Ice refers to the area of the Arctic Ocean covered by ice. The Arctic sea ice minimum is the day in a given year when Arctic sea ice reaches its smallest extent, occurring at the end of the summer melting season, normally during September. Arctic Sea ice maximum is the day of a year when Arctic sea ice reaches its largest extent near the end of the Arctic cold season, normally during March. Typical data visualizations for Arctic sea ice include average monthly measurements or graphs for the annual minimum or maximum extent, as shown in the adjacent images.
Sea ice extent is an alternative measurement and is usually defined as the area with at least 15% of sea ice cover. This metric is used to address uncertainty in distinguishing open sea water from melted water on top of solid ice, which satellite detection methods have difficulty differentiating. This is primarily an issue in summer months.
Sea ice and climate feedbacks
Arctic Sea ice maintains the cool temperature of the polar regions and it has an important albedo effect on the climate. Arctic Sea ice melts in the summer, and more of the sun is being absorbed by the ocean. The fast rate of the sea ice melting is resulting in the oceans absorbing and heating up the Arctic. The decline in sea ice does have a potential to speed up global warming and the climate changes.
An "ice-free" Arctic Ocean is often defined as "having less than 1 million square kilometers of sea ice", because it is very difficult to melt the thick ice around the Canadian Arctic Archipelago. The IPCC AR5 defines "nearly ice-free conditions" as sea ice extent less than 106 km2 for at least five consecutive years.
The fishermen know that the sea is dangerous and the storm terrible, but they have never found these dangers sufficient reason for remaining ashore.
Many scientists have attempted to estimate when the Arctic will be "ice-free". Professor Peter Wadhams of the University of Cambridge is among these scientists; Wadhams in 2014 predicted that by 2020 "summer sea ice to disappear," Wadhams and several others have noted that climate model predictions have been overly conservative regarding sea ice decline. A 2013 paper suggested that models commonly underestimate the solar radiation absorption characteristics of wildfire soot.
In 2007, Professor Wieslaw Maslowski from the Naval Postgraduate School, California, predicted removal of summer ice by 2013; subsequently, in 2013, Maslowski predicted 2016 ±3 years. A 2006 paper predicted "near ice-free September conditions by 2040". Overland and Wang (2013) investigated three different ways of predicting future sea ice levels. From sea ice models and recent satellite images it can be expected that a sea ice free summer will come before 2020. The IPCC AR5 (for at least one scenario) estimates an ice-free summer might occur around 2050. The Third U.S. National Climate Assessment (NCA), released May 6, 2014, reports that the Arctic Ocean is expected to be ice free in summer before mid-century.
Models that best match historical trends project a nearly ice-free Arctic in the summer by the 2030s. However, these models do tend to underestimate the rate of sea ice loss since 2007. Based on the outcomes of several different models, Overland and Wang (2013) put the early limit for a sea ice free summer Arctic near 2040. Professor James Anderson of Harvard University envisions the Arctic Ice gone by the early 2020s. "The chance that there will be any permanent ice left in the Arctic after 2022 is essentially zero," he said in June of 2019.
Amplified Arctic warming
Dark, open water left behind as sea ice melts absorbs vastly more heat than ice covered water, leading to physical implications that include the ice-albedo feedback or warmer sea surface temperatures which increase ocean heat content. This also increases pressure and decrease wind speeds. These feedback effects are stronger in the lower atmosphere. As Peter Wadhams, a polar researcher writes "once summer ice yields to open water, the albedo ... drops from 0.6 to 0.1, which will further accelerate warming of the Arctic and of the whole planet."
There has been debate whether the Arctic Ocean will pass a "tipping point", defined as a threshold for abrupt and irreversible change, as the amount of ice cover declines. Although some earlier studies supported the presence of a tipping point, the IPCC AR5 concluded that there is little evidence for such a tipping point based on more recent studies that used global climate models and low-order sea ice models. However, a 2013 study identified an abrupt transition to increased seasonal ice cover variability in 2007 which persisted in following years, which the researchers considered a non-bifurcation 'tipping point', with no implications of irreversible change. The IPCC AR5 WGII report stated with medium confidence that precise levels of climate change sufficient to trigger a tipping point remain uncertain, but that the risk associated with crossing multiple tipping points increases with rising temperature.