The extent of sea ice in the Arctic has dropped dramatically. Here’s the data from NSIDC (the National Snow and Ice Data Center):



The thin black line shows daily values of sea ice extent. Clearly it rises and falls each year, with more ice in winter/early spring and less during summer/early fall. The red dots show the annual maximum values, the blue dots the annual minimum values, and the brown dots show the yearly average values.

The minimum values tend to get more attention than either the maximum or yearly average values. Some people even go so far as to ignore most of those, instead talking only about minimum values from 2007 onward (what’s inside the red box):

We have data for each day over nearly 40 years, we have annual averages for 39 years, and both yearly maxima and minima for 40 years. But for some reason, some people (as in, most climate deniers) only want to talk about 12 minima. Why do you think that is?

I’d like to try something I find interesting. The downward trend in Arctic sea ice was detectable by the end of the 1900s, and we’re interested in whether or not the situation has improved since then, so I’ll take trends estimated from pre-2000 data and extend them up to the present, to see how observations compare to what we would have predicted from the existing linear trend.

We’ll start with the yearly minimum values:

Since 2000, the situation didn’t get better. It got worse.

Yet climate deniers only like to talk about the minimum values since 2007, and they love to declare a “recovery!” in Arctic sea ice. Look at the above graph again: does that look like a recovery to you?

It’s a classic case of cherry-picking — selecting only the data that make you case look good and ignoring the rest. They also don’t generally run valid statistical tests to establish that some real improvement happened. That’s probably because such tests fail.

Here are the yearly maximum values:

There’s definitely no improvement since 2000. It appears to have followed the pre-existing trend pretty closely, and note that the two lowest values are in the last two years, the four lowest values are in the last four years.

Here are the yearly average values:

Again, no improvement, no recovery. The two lowest values are in the last two years, the three lowest values in the last three years. It’s not better than it would have been if it had followed the pre-existing trend; it’s worse.

Arctic sea ice is important for many reasons. For one thing, when ice changes to open water it absorbs more of the sun’s incoming energy, reflecting less back to space, and that warms up the planet even more — it’s one of the classic feedbacks in the climate system. For another thing, removing sea ice allows more heat transfer from ocean to atmosphere in the Arctic, and that dramatically changes wind circulation patterns. It seems to be making the jet stream more wavy, which allows weather systems (including unpleasant ones like heavy rain or heat waves) to be more persistent so bad conditions hang around longer. The effect is profound, and it’s worldwide. Arctic sea ice is something we should talk about more often.

But when climate deniers talk about Arctic sea ice, they paint a rosy picture of “recovery.” It’s a sham, based on blatant cherry-picking and statistical incompetence. It’s also a threat to all of us who are affected by it. Let’s not let the conversation be dominated, or even polluted, by the ignorant and misleading pollution coming from the mouths of climate deniers.

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