Friday, October 14, 2016

Arctic Sea Ice Extent Continues to Decrease

September 2016 saw a tie for the second lowest Arctic sea ice extent ever recorded. The minimum extent, occurring on September 10th this year, was 4.14 million square kilometers. NSIDC said this was tied for second lowest extent with the 2007 minimum of 4.154 million square kilometers, which occurred on September 18, 2007. That doesn't look like a tie to me, but the people at NSIDC are the experts and the ones who get to decide - so a tie it is.

The fact that the extent was so low is important, but we are more concerned with a trend than a single datum point. And, the trend is not good.

Source: NSIDC
NSIDC reports the September minimum extent is declining at a rate of 87,200 square kilometers per year (13.3% per decade). If this rate continues, we will see an ice free Arctic on a regular basis starting some time in the mid-2060s (4.14 million square kilometers divided by 87,200 square kilometers per year = 47.5 years).  Of course, as we can see by the graph above, the actual extent varies considerably from year-to-year. Therefore, we can expect to see an isolated case of an ice-free Arctic before that time.

But, we still haven't examined the most important aspect of the sea ice. The fact is, the Arctic sea ice extent has a downward trend for every month of the year. Over time, the sea ice extent is getting smaller every year for every month of the year. Most disturbingly, this is even true for March, when the maximum ice extent normally occurs:

Source: NSIDC

This year's maximum was the lowest every recorded at 14.52 million square kilometers on March 24, 2016. The average extent for March was the second lowest average, after only March 2015. The maximum extent is declining at a rate of 42,100 square kilometers per year (2.7 percent per decade). At that rate, we will see an Arctic Ocean that never freezes over within 350 years. Hopefully, we'll take actions before then and prevent that from happening. But, the very fact that we need to discuss it at all is disturbing. 

One of the things that is lost in the discussion is the fact that the planet's axial tilt is not changing with global warming. We are still tilted at 23.5 degrees relative to the ecliptic plane. This means the poles each have one sunrise and one sunset per year, spending six months in darkness during their respective winters. The orbital mechanics causing winter have not changed. So, how is it the sea ice maximum extent is decreasing? We still have the same amount of darkness as before, that hasn't changed. So, why is the ice extent decreasing?

Of course, the anti-science people make various claims. One person, in a comment on this website, recently said the ice extent isn't decreasing at all. This person stated the minimum occurred in 2012 and has been increasing ever since. In response to that, I encourage everyone to take a look at the two graphs above. Not only do both show a clear downward trend, but they show this trend has continued in recent years when you leave out the anomalous year of 2012. Selecting one year and using that as the only datum point is the absolute extreme case of cherry-picking.

Other claims are that it isn't global warming that is responsible for this decrease,but natural weather variations, most commonly the Arctic Oscillation (AO). This shows just how little science the anti-science people understand. Here is a plot of the AO over time:

Source: NOAA
When the AO is in a positive phase, winds circulate around the Arctic and trap cold air masses in the north. When it is in a negative phase, the winds weaken and the cold air mass can move southward and be replaced by warm air moving in. The claim is the AO has been mostly negative and this is what is causing the warming in the Arctic. But, as you can see, the AO switches back and forth with a great deal of variability. So, how is it that this accounts for the loss of sea ice?

The fact is, sea ice extent is decreasing on a regular trendline. This cannot bode well for the climate, the environment and for us.

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