27 August 2012

Arctic sea-ice melt record more than broken, it’s being smashed

by David Spratt, first posted 25 August 2012
UPDATE 27 AUGUST: Sunday's data confirms that the previous sea-ice extent minimum of 24 September 2007 was broken last Friday, 24 August 2012. What is also stunning are sea-ice daily extent figures averaging ice loss of more than 100,000 square kilometres per day for the last four days. This suggest melt is accelerating very late in the melt season in a pattern that has never before been observed. The Arctic this year is heading into new territory and it looks like 2012 may in retrospect be seen as the year when a new melt regime took hold.
      The ice extent is about to drop below 4 million square kilometres for the first time in the satellite record, and the Arctic has shed almost half a million square kilometres of sea-ice in last five days! With three weeks of the melt season still to go, it's not hard to see extent dropping another half a million square kilometres (or more!) to 3.5 million square kilometres. (In previous big melt years of 2007 and 2011, around half a million square kilometres was lost after 26 August.)
    This is starting to make the second graph (below) looking reasonable, and those scientists and models which have been suggesting an sea-ice-free summer Arctic within a decade to be on the money.
     The commentary by Climate Commissioner Prof. Will Steffen in today's newspapers that ''We can expect to see an ice-free Arctic at about the middle of this century'' looks out of touch with the most recent data, and exhibits IMHO a scientific reticence which does a disservice to the urgent public debate we need on implications of the Arctic melt for Australian climate policy (and sea-level rises from Greenland!). Positive feedbacks now have a grip on Arctic sea-ice and the descent appears to be exponential, not linear. Looking at the PIOMASS date on sae ice volume (fifth chart here), its hard to know what Prof. Steffen  has based his assertion upon.
      Perhaps the enormity of the present situation is best summed up by sea-ice blogger Neven: "Basically, I'm at a loss for words, and not just because my jaw has dropped and won't go back up as long as I'm looking at the graphs. I'm also at a loss - and I have already said it a couple of times this year - because I just don't know what to expect any longer. I had a very steep learning curve in the past two years. We all did. But it feels as if everything I've learned has become obsolete. "
Climate change impacts are frequently happening more quickly and at lower levels of global warming than scientists expected, even a decade or two ago. And this week the Arctic has provided a dramatic and deeply disturbing example.
     According to IARC/JAXA satellite data at Arctic Sea-ice Monitor from the Japan Aerospace Exploration Agency, the sea-ice extent of 24 August 2012 of 4,209,219 square kilometres broke the previous record in the satellite era of 4,254,531 square kilometres set on 24 August 2007. Back then the were scientific gasps that the sea ice was melting “100 years ahead of schedule”.
JAXA Arctic sea ice extent to 24 August 2012. Updates: http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm

What is astounding is that the record has been broken with three to four weeks of the melt season to go, and that the rate of melting this month is unprecedented in the modern record. Check the chart above (click to enlarge), with the red line mapping 2012 sea-ice extent. The slope of the line is much steeper than in previous years for August.
     Looking at the data, the daily rate of sea-ice loss for 1-24 August has been 99,029 square kilometres per day in 2012, compared to:
  • 2007   62,976 square kilometres per day
  • 2008   72,785 square kilometres per day
  • 2009   53,859 square kilometres per day
  • 2010   55,109 square kilometres per day
  • 2011   63,342 square kilometres per day
  • 2012   99,029 square kilometres per day
And last three days have been 119,219, 128,281 and 122,188 square kilometres per day (they use 2-day running average, so last figure subject to revision).
     It is remarkable that rate of loss is so much greater than previous years this late in the melt season, and at present shows no sign of easing.
     The ice is now much thinner on average than in the past, as the extent of multi-year ice declines sharply. Thin ice is easily smashed up by storms and rough seas, and that’s what’s happened this year. In early August, a huge, long-lived Arctic ocean storm decimated the sea ice area which was melting out at a record rate, before the high waves and winds shattered the Siberian side of the ice cap.  But there have been subsequent, less well-reported, cyclonic storms churning up the ice, which may explain why the melt rate has not eased off in the last 10 days.
     What the minimum extent will be this year is anybody’s guess. It depends on weather conditions over the next three weeks, and how much ice is now just above the threshold (of 15 per cent sea-ice in a given area) and is currently counted as sea-ice, but likely to be below the threshold by the third week of September.
     Even if the ice loss over the next 3-4 weeks was similar in magnitude to previous recent years, the season low could be around 3.5 million square kilometres. Maybe a good bit more, perhaps somewhat less. We will have to wait and see.
     The next chart, amended, from NSIDC shows the 2007 fourth IPCC report projections for Arctic sea ice (blue line) and projections for RCP4.5 (representative concentration pathways) (red line) being used for the forthcoming fifth IPCC report in 2014. Actual observations are in black, and I have taken the liberty of sketching in grey what it will look like if the 2012 figure is around 3.5 million square kilometres.
Sea-ice extent projections versus observations. My 2012 guestimate in grey. (Pink and blue shading show 1 standard deviation from averaging results from all of the model runs)
The implications have been discussed on this blog many times before: we are likely heading to a summer sea-ice-free Arctic in the next decade, a view becoming more commonplace in the research community.
     With Greenland passing its previous record melt on 8 August – with more than a month of the melt season left – it seems to be an extraordinary year, but the record show it may be the new norm as the Arctic warms at two-to-four times the global average, and increasing areas of exposed sea are absorbing vast amounts of energy that would previously been reflected by ice.
     Which makes a blog – Saving the Arctic is environmentalism's biggest challenge yet – by Greenpeace director John Sauven, in Friday’s Guardian intriguing:
The Arctic is home to millions of people, including Inuit whose ancestors first settled thousands of years ago. It is also a unique ecosystem, home to some of the most extraordinary species on Earth, from the narwhal to the walrus to the polar bear. For hundreds of other migratory species, including humpback whales and Canada geese, it is a vital summer feeding ground.
The amazing Arctic also plays a critical role in regulating our climate. The Arctic sea ice is like a giant mirror that reflects much of the sun's energy, helping to keep our planet cool. The formation of Arctic sea ice produces dense salt water which sinks, helping drive the deep ocean currents. Without the ice, this delicate balance will be upset and could cause profound regional and global climatic changes.
We all rely on the Arctic for our survival. And now we are in danger of losing one of the world's great ecosystems and an important life support system leaving all species facing an increasingly insecure and uncertain future.
Sauven says that “Greenpeace needs the support of millions if it is to save the Arctic from destruction by the oil industry”. Sure, we don’t want an oil industry in the Arctic, but that is not what is destroying it right now. Climate change is, and it is now very late in the day, as the charts above testify.
     To save the Arctic from climate change, the big melt in the last decade needs to be reversed. For sea ice that is not too difficult because sea-ice feedbacks (warmer temperatures, more melt; cooler temperatures, more ice re-forms) work on short time frames.  The sea ice is in a “death spiral” at global warming of just 0.8 degrees Celsius, yet the current level of greenhouse gases would in the longer run warm the planet by more than 2C. So it’s not just a case of halting greenhouse gas emissions, but reducing (drawing down) the current level of atmospheric carbon, and finding some way to reduce the warming in the Arctic till than can be done (discussed here). An Australian Safe Climate Transition Plan Strategic Framework is available here.
     Given what is happening at just 0.8C, its pretty obvious that global warming would need to be brought down to no more than 0.5C, if not lower. That’s about 310 parts per million atmospheric (ppm) carbon dioxide, compared to the current level of 390 ppm and the pre-industrial level of 280ppm.
     That’s what Sauven’s challenge to “Save the Arctic” really means.