I presume that John was referring to two-season ice, which is not usually considered as multi year ice. Two year ice can be rather weak.
What is important on Pen Hadlow's sea ice thickeness that 2,500 holes from Canada to the North Pole produced an average thickeness of 177.4 cm. In my experience ice of thickeness 120 cm will melt away by second week of July. So the margin is 57.4 cm. There aren't lots of leeway as some of the ice fell below average and must be closer to the tipping point. All those ice areas with only 120 cm will definitely melt, perhaps those 150 cm. It all depends how good start the melting gets. The sea ice on its last legs will behave very differently than ice that was before. Wave penetration, reduced sea ice area all influence the vertical mixing of sea water and make ice more motionary, mopping up heat when ice encounters open (warmed) waters. The localised vertical mixing of sea water is also very dangerous for ice in stormier conditions if there are open water and ice travelling with it. Ice is propelled by wind providing a drag as well as higher windward water column against the trough side. The higher watercolumn on the windward will produced pumping which raises deep water up nearby. We'll see how things develop but the computer models are as good as that keeping as flying models when unanticipated processes kick in and are not put in the models. Please note that I have been constantly saying since 2005 that we might get ice free ocean by end of decade due to a number of things, which I have occasionally mentioned. I am worried about the methane coming from the warming soils, more intensive decay, methane clathrates and the possibility (likelihood?) of strong and swift coupling with marine and terrestrial ice losses in the Arctic (i.e. Greenland ice sheet whole scale land containment failure developing shortly in post-sea ice Arctic as expressed by HE President Morales in Poznan and some other advocates). Regards, Albert Date: Mon, 8 Jun 2009 18:47:43 -0400 Subject: [geo] Re: Arctic sea ice - no multi-year ice found From: dwschn...@gmail.com To: j...@cloudworld.co.uk CC: geoengineering@googlegroups.com; vicky.p...@metoffice.gov.uk; john.do...@ec.europa.eu; bbur...@cleanair-coolplanet.org; robert.wat...@uea.ac.uk; will...@parliament.uk John: Of course there is multi-year Arctic sea ice. You may want to take a look at a fascinating display of Arctic sea ice photo's arranged as a movie video on YouTube, available here, with explanation on what was done and how. http://wattsupwiththat.com/2009/05/31/arctic-sea-ice-time-lapse-from-1978-to-2009-using-nsidc-data/ This video shows a 31 year progression of freezing and melting over the pole. When you get to last year and this year, you will see the summer conditions show plenty of ice still in the Arctic sea and upon which still more snow has fallen this year. That is not to say it couldn't all just plain disappear, but at this point, it is incorrect to say that there is simply no multi-year ice. Anyone who looked and didn't find it is simply looking in the wrong place. David. On Mon, Jun 8, 2009 at 5:57 PM, John Nissen <j...@cloudworld.co.uk> wrote: It is now accepted by most scientists that the Arctic sea ice retreat is caused by anthropogenic global warming, though the exact mechanism for the "polar amplification" of global warming is not well understood. Critical for sea ice survival is the multi-year ice. In his recent measurements of Arctic sea ice, Pen Hadow found absolutely no multi-year ice, and the one-year ice was about 4 foot thick. This is extremely disturbing, because the one-year ice can melt away very suddenly, given warm weather. So when Vick Pope says that the sea ice could disappear "later this century", it is a gross understatement of the danger. The Pen Hadow finding shows that the sea ice could disappear quite suddenly, if the natural variation in Arctic weather led to a much warmer than average summer, such as in 2007 only more so. http://vodpod.com/watch/1634449-british-team-finds-no-multi-year-ice The implications are: 1. The risk of massive methane outgassing is increased. 2. The risk of Greenland ice sheet destabilisation is increased. 3. Emissions reductions by end century will certainly be too late, even if they were to have a cooling effect in the Arctic. 4. Geoengineering in the Arctic must now be deployed for cooling the Arctic. 5. The sooner it is deployed the better, providing it is done carefully to reduce risk of adverse side-effects. 6. Black carbon levels must also be reduced, as they help to melt snow and ice in the Arctic. Now I know that Vicky Pope considers that this is being apocalyptic. But actually it's all about risk management. The very argument she uses about variability actually increases the risk that the sea ice disappears much sooner than expected, as a violent swing on one side of the trend line. This is what Vicky was writing in the Guardian in February this year: http://www.guardian.co.uk/environment/2009/feb/11/climate-change-misleading-claims [quote] Pope says there is little evidence to support claims that Arctic ice has reached a tipping point and could disappear within a decade or so, as some reports have suggested. Summer ice extent in the Arctic, formed by frozen sea water, has collapsed in recent years, with ice extent in September last year 34% lower than the average since satellite measurements began in 1979. "The record-breaking losses in the past couple of years could easily be due to natural fluctuations in the weather, with summer ice increasing again over the next few years," she says. [end quote] The result of this optimistic view of sea ice survival, promoted by the IPCC and continued by the Hadley centre, is that governments are blissfully unaware of the risk of sea ice disappearance and repercussions. Furthermore, they are still being led to believe that emissions reduction alone can halt global warming before tipping points (such as sea ice disappearance) are reached. This is absolute nonsense, since there is no way that emissions reduction can cause a cooling effect in the Arctic. In the same article, Vicky Pope said "the implications of climate change are profound and will be severe if greenhouse gas emissions are not cut drastically" - but if governments focus on emissions reduction alone, there is the danger of sea ice disappearance taking us all by surprise. And then it will be too late. Cheers, John -- David W. 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