by Judith Curry
It looks like the Arctic sea ice is close to reaching its seasonal minimum, reflecting a substantial increase in sea ice relative to the record breaking minimum in 2012.
A year ago, September 2012, the Arctic sea ice extent had already broken the previous satellite-era record set in 2007 and climate watchers were wondering how low it could go. The 2012 sea ice minimum reached a record low of 3. 6 M sq km. What this implied for the future of Arctic sea ice has been the subject of hot speculation. For my own take on this subject, see my post at Climate Dialogue, which was based on several previous posts at Climate Etc.:
- Pondering the Arctic Ocean. Part I: Climate Dynamics
- Likely causes of recent changes in Arctic sea ice
- Reflections on the Arctic sea ice minimum: Part I
- Reflections on the Arctic sea ice minimum: Part II
Usually, I have waited until the NSIDC declares an official end to the Arctic sea ice melt season to write an article on this topic. The timing of my article this year is motivated by David Rose’s article in the Sunday Mail entitled Record return of Arctic ice cap as it grows by 60% in a year with top scientists warning of global cooling. Apart from the rather lurid title, there is some good material here (including some quotes from moi). Excerpts:
A chilly Arctic summer has left nearly a million more square miles of ocean covered with ice than at the same time last year – an increase of 49 per cent. UPDATE: David Rose has updated his original article, to fix an error on the NSIDC web page.
The rebound from 2012’s record low comes six years after the BBC reported that global warming would leave the Arctic ice-free in summer by 2013.
Instead, days before the annual autumn re-freeze is due to begin, an unbroken ice sheet more than half the size of Europe already stretches from the Canadian islands to Russia’s northern shores.
Rose then goes on to discuss the global temperature pause, motivated largely by my previous post Pause tied to equatorial Pacific cooling:
In its draft report, the IPCC says it is ‘95 per cent confident’ that global warming has been caused by humans – up from 90 per cent in 2007.
This claim is already hotly disputed. US climate expert Professor Judith Curry said last night: ‘In fact, the uncertainty is getting bigger. It’s now clear the models are way too sensitive to carbon dioxide. I cannot see any basis for the IPCC increasing its confidence level.’
She pointed to long-term cycles in ocean temperature, which have a huge influence on climate and suggest the world may be approaching a period similar to that from 1965 to 1975, when there was a clear cooling trend. This led some scientists at the time to forecast an imminent ice age.
JC note: in response to a specific question regarding what happens when both the AMO and PDO are in the cool phase, I pointed to the previous period 1965-1975 when both were in the cool phase.
Professor Anastasios Tsonis, of the University of Wisconsin, was one of the first to investigate the ocean cycles. He said: ‘We are already in a cooling trend, which I think will continue for the next 15 years at least. There is no doubt the warming of the 1980s and 1990s has stopped.
Others are more cautious. Dr Ed Hawkins, of Reading University, drew the graph published by The Mail on Sunday in March showing how far world temperatures have diverged from computer predictions. He admitted the cycles may have caused some of the recorded warming, but insisted that natural variability alone could not explain all of the temperature rise over the past 150 years.
Nonetheless, the belief that summer Arctic ice is about to disappear remains an IPCC tenet, frequently flung in the face of critics who point to the pause.
Yet there is mounting evidence that Arctic ice levels are cyclical. Data uncovered by climate historians show that there was a massive melt in the 1920s and 1930s, followed by intense re-freezes that ended only in 1979 – the year the IPCC says that shrinking began.
Professor Curry said the ice’s behaviour over the next five years would be crucial, both for understanding the climate and for future policy. ‘Arctic sea ice is the indicator to watch,’ she said.
As per Twitter, Ed Hawkins says that he was quoted correctly. My direct quotes are correct; the statement regarding the period 1965-1975 is put into my intended context in my note above.
In summary, I think the ‘cooling’ aspect has been overplayed in the arcticle; I think we are mostly talking about the absence of the predicted surface warming which has manifested itself in the pause since 1998 and even a slight cooling trend since 2002. But I imagine that it is difficult for a journalist to argue against the overhyping of the pause and the cooling, given the anticipated dismissal of the pause by the IPCC.
Forecasts of the 2013 sea ice minima
The Search Sea Ice Outlook is an international effort to provide a community-wide summary of the expected September arctic sea ice minimum. The average of all these forecasts for 2013 was 4.1 M sq km (compared to an average of 4.4 sq km for 2012).
One of the most sophisticated models used in seasonal sea ice forecasting is the UK Met Office model, which includes the state-of-the-art sea ice model used in climate model applications (CICE). The UKMO forecast (experimental) was for 3.36 M sq km +/- 1.5 M sq km, where the range is provided by an ensemble of simulations (compared to 4.4 +/- 0.9 M sq km for 2012).
As per Cryosphere Today, the current sea ice area is 4.746 M sq km. This is a whisker above the 2009 minimum, which is the highest minimum since 2007.
Natural interannual and multi-decadal variability
So . . . to what extent is the current mini-maxima in the seasonal sea ice extent minimum attributed to interannual variability, or perhaps part of a mini-decadal shift? It is very frustrating not to have adequate sea ice data prior to the satellite record to address this issue. Tony Brown provides a fascinating perspective on historical sea ice variability 1920-1950 in this previous CE post.
In terms of natural variability, I have found it fascinating to watch the regional variation of the sea ice, which is facilitated by a new WUWT reference page on Northern Regional Sea Ice.
- Regions that are anomalously high: Baffin Bay Gulf of St Lawrence, Beaufort Sea, Canadian Archipelago, Chukchi Sea, East Siberian Sea, Kara Sea.
- Regions that remain anomalously low: Central Arctic, Greenland Sea
For geographic reference, see this map (copyrighted so I can’t reproduce here).
In trying to sort out how much of the recent sea ice variability is driven by the atmosphere (weather), the ocean (longer-term variability) and CO2 forcing, I am paying particular attention to regional variability. I think that weather played a major role in the 2012 minima; I am suspecting that the oceans are playing the major role this year in the recovery. In fact, the past year might be associated with a mini climate shift in the ocean circulation regimes, but not on the magnitude of the 1976 and 2002 shifts. Keep your eye on the Kara Sea. And be on the lookout for a new paper that I am co-author on that is hopefully in the final stage of review.