page_title: Arctic sea ice decline
section_title: Ice-free summer
hierarchical_section_title: Arctic sea ice decline / Ice-free summer
caption_attribution_description: English: NORTH POLE North Pole Keep
context_page_description: 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 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, dominated by a later autumn freeze-up. Sea ice changes have been identified as a mechanism for polar amplification.
context_section_description: An "ice-free" Arctic Ocean, sometimes referred to as a "Blue Ocean Event", 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.
  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. 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 2019.
  Warming Arctic temperatures provide a powerful forcing toward lessened sea ice coverage.
caption: The dark ocean surface reflects only 6 percent of incoming solar radiation; instead sea ice reflects 50 to 70 percent.[19]
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