Monday, February 20, 2017

But the Trend is Still Up!

While both of the polar sea ice extents are low, Antarctic sea ice is just plain ridiculous.

Yesterday its extent set a new low for the satellite era, at 2.20 Mkm2. (The previous low was 2.26 Mkm2, way back in 1997.)

Amazingly, present Antarctic SIE is 16% below last year's value at this time. Last year's low was 2.58 Mkm2.

But the long-term trend, starting with the satellite data on 10/26/1978, is still very much upward, at 18.3 Kkm2/yr. That's down from its maximum of 23.7 Kkm2/yr in July 2015.

Perhaps this year is mostly noise and the ice will rebound. On the other hand, if this year represents a tipping point, as some think happened with Arctic SIE years ago, it won't. But if has fallen a large amount in just the last two years:

{This last graph is the 365-day moving average, and not corrected for leap years. With over 38 years of data, the 365-day moving average would have now fallen back about 9-10 days -- that is, what was once a Jan1-Dec31 average is now about a Dec23-Dec22 average. So probably worth fixing.}


Harry Twinotter said...

I am hedging my bets and say the downturn in Antarctic sea ice extent is natural variation. 2016 was an unusual year with the El Nino and the very warm Indian ocean. Total speculation on my part of course.

David Appell said...

Harry: If I had to bet, I would bet to agree with you.

Toby said...

Gerald Meehl has made a prediction that the return of the Interdecadal Pacific Oscillation to a positive phase will lead to a downturn in average Antarctic Sea Ice extent. I read this somewhere and cannot now find where. But here is Meehl's paper.

This would indeed be natural variability, it will be interesting to see how the long term trend pans out.

Layzej said...

FWIW, I tend to agree with you. The change is almost too large and too quick to be anything other than noise. But out of curiosity, what would it take before you would suspect that this is not just noise but actually a change in the trend?