Something strange is happening in the Arctic. For two days in November, the Arctic sea ice did not behave as expected. 
Arctic sea ice increases in winter and shrinks in summer, and scientists keep a close eye on how much it increases or shrinks by. That’s because Arctic sea ice is a key indicator of how global warming is affecting the planet. This November, something happened that had everyone puzzled. 
Sea ice extent reaches record lows
We already know that 2016 is shaping up to be the hottest year on record. At the same time, the Arctic sea ice extent – the amount of sea that is turning to ice – is showing record lows. 
In October, the Arctic sea ice extent began to set new daily record lows for this time of year, according to the National Snow and Ice Data Centre.
This means that less of the Arctic Ocean is turning to ice than ever before, as this map shows.
Sea ice extent (Oct 2016)
Image: National Snow and Ice Data Center
The pink lines on this map show the average sea ice formation from 1981 to 2010. The white area shows this October’s ice formation. 
Arctic sea ice extent averaged 6.40 million square kilometers, the lowest October in the satellite record. This is 400,000 square kilometres less than October 2007. 
Strange happenings
The Arctic sea ice extent has been steadily shrinking in the last few years. This graph shows the areas of ocean that are shrinking year on year by at least 15%. 
The strange thing is that this November, the sea ice might have shrunk at the exact time of year that it should be increasing. 
Arctic sea ice
Image: National Snow and Ice Data Center
The graph shows that on 19 November, the extent of Arctic sea ice was nearly 1 million square kilometers lower (8.633 million vs 9.504 million) than it was on that date in 2012.
The next day, the gap widened further, with 8.625 million square kilometers in 2016 versus 9.632 million in 2012.
“Over the past few days, extent has actually decreased in the Arctic, and while I don’t think that such a short-term decline is unprecedented for this time of year, it is highly unusual, for November is a month when we normally see a quite rapid ice growth,” Mark Serreze, director of the National Snow and Ice Data Center told the Washington Post.

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Why is it happening?
It’s because of higher-than-usual sea surface temperatures, and unusually high air temperatures. 
This year the Arctic sea ice has retreated earlier than normal, meaning that the sea had longer to absorb the heat from the sun. As a result, at the start of the season when sea ice should be forming, the water was still too warm. 
Air temperature also played a part. October’s air temperatures were unusually high over most of the Arctic Ocean for that time of year.
Global surface temperature
Image: ClimateReanalyzer.org
Why does it matter?
Most of us will never lay eyes on it, but the ice in the Arctic affects the entire planet. It regulates global temperature and if it gets warmer there, our weather systems change. Without Arctic sea ice, the global climate will change dramatically.
The shrinking ice also affects local populations and wildlife, putting them in danger.