Question: By how many days per decade has the melt season lengthened in the shallowest of the world's major oceans?
Related documents: [0]  [DOC] Arctic sea ice decline is the sea ice loss observed in recent decades in the Arctic Ocean. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report states that greenhouse gas forcing is largely, but not wholly, responsible for the decline in Arctic sea ice extent. A study from 2011 suggested that internal variability enhanced the greenhouse gas forced sea ice decline over the last decades. A study from 2007 found the decline to be "faster than forecasted" by model simulations. The IPCC Fifth Assessment Report concluded with high confidence that sea ice continues 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 40,000 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 freezeup. Sea ice changes have been identified as a mechanism for polar amplification. [END] 
[1]  [DOC] The Arctic Ocean is the smallest and shallowest of the world's five major oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea or simply the Arctic Sea, classifying it a mediterranean sea or an estuary of the Atlantic Ocean. Alternatively, the Arctic Ocean can be seen as the northernmost part of the all-encompassing World Ocean. [END] 
Answer: 
5 days per decade
5 days per decade