Sunday, June 29, 2014

The Great Arctic Ice Recovery of 2013

One of the more common claims deniers make is that the Arctic sea ice recovered in 2013 and that the issue of the vanishing Arctic sea ice is no longer valid. Frequently, this issue is pulled out as evidence that global warming is not real, or at least over blown.

Let's look at the facts to see the validity of these claims.  Below is a plot from the National Snow and Ice Data Center (NSIDC) showing the amount of Arctic sea ice. The solid black line is the long-term average. The dotted line on the bottom is the data from 2012, which was a catastrophic year and, by far, the year with the lowest amount of sea ice. The line in between those two is the data from 2013. As you can see, the ice made a recovery, but not even to the average.

Source: NSIDC

To put it another way, look at this similar graphic. This time we still have the long-term average as the black line, but the two lines below it represent the data for 2013 and for 2009. The 2013 ice data is very similar to the 2009 levels. In other words, the ice in 2013 recovered to only about the 2009 level.

Source: NSIDC

What does that mean when I say it recovered to 2009 levels? Take a look at this plot of the September sea ice extent (annual minimum extent) over time.

Source: NSIDC

You can easily see the big dip in 2012 and the recovery that occurred in 2013 as the last two data points on the right. Start at the 2013 data point (the last plus mark) and make a horizontal line to the left to compare it to previous years. You can see it is about the same as 2009. Otherwise, there are only five data points that are lower and that is going back all the way to 1979.

There is a clear downward trend to the plot above, but the individual years go up and down. There is nothing surprising about that. We can see that 2012 was an abnormally bad year. Likewise, 2013 was a nice recovery that we hope will continue. But, you can't make judgements about the trend based on one, or even two years. If scientists were to make claims based on just 2012 alone, it would be as wrong as deniers making claims based on 2013 alone. The long-term trend is what is important.

So, will the trend continue in 2014, or did 2013 represent the start of a new trend? Let's look. Below is a plot showing the ice data for this year (as of June 28). Again, the long-term average is the black line. The complete curve is for 2013 and the partial curve is for what has happened so far this year.

Source: NSIDC

The ice data for this year is consistently tracking at below last year's. Granted, it is only a little bit below and there is a lot of melt season remaining, so there could be some significant changes in this graph by September. Remember, though, those significant changes could go either way. The point I'm making here is that we are not seeing evidence of a recovery, we are seeing evidence that the data is returning to the trend line.

Look at this plot.This is the ice surface temperature and comes from the Danish Polar Portal. The North Pole is located in the middle of the figure. The color of the ice represents the temperature according to the scale on the bottom. The white areas are areas where data was not collected due to cloud cover. The coldest areas are typically north of Greenland, where the large white area is in this plot. But, the rest of the Arctic region is either close to 0 degrees Celsius or above. In other words, its melting.

Source: Polar Portal

This temperature distribution is about average for this time of year and there is thickness to the ice, so we are not looking at some major collapse of the sea ice. But, the evidence does not support claims that the sea ice extent has recovered. I hope it does recover because this is a critically important part of the world in regards to weather. The data, though, is indicating the reduction in sea ice extent will continue pretty close to the long-term trend.

I will post updates as the melt season continues.

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