sunny starry skies

Without spare Earths on which to run the experiment, the models are the best we have. The contribution from CO2 is ~0.5-0.8C, and there is little reason to suggest it would be different with the additional forcings coded in, seeing as both the 'with' and 'without' model experiments are lacking in the same things. Of course you can always suggest that since there are specific uncertainties we therefore have no idea what is going on, but that would be rather negative, don't you think? CJWRC, what evidence do you have for thickening ice in the Arctic? Surely you're not using the PIPS 2.0 model where the ice thickness estimates are not validated, and volume estimates by numpties such as steven goddard do not take into account concentration data or the fact that PIPS reports maximum thicknesses (so that subs do not surface under ice too thick...)? The PIPS model is specifically not intended to be a climatologic resource for ice thickness data, whereas the PIOMAS mode validates the PIPS data to come up with realistic volume values. Both, of course, are models, but PIOMAS at least is validated, and shows a rapid decline.

Er, Y.S., you keep repeating this false assertion about 'assumed' feedbacks.  In fact the feedbacks are a natural product of the physics in the models, not specifically coded in. They are also observed.  You seem to be trying to mislead people into thinking that the feedbacks don't actually exist, that climate scientists invent them for fun or something.  Without the positive feedbacks, it is impossible to cycle from glacial to interglacial state and back again - climate sensitivity to CO2 variations would be ~1C/doubling, and glacial-interglacial transitions would have been a fraction of their size.  What produces the feedbacks - rather simple physics!  The ice-albedo feedback is obvious, the water vapour feedback is also straightforward (warmer air holds more water vapour), and there are a host of otehr positive feedbacks.  They are not 'assumed', as you would have to break the physics in order to remove the feedback, for example assuming that both light and dark surfaces reflect equally well. Feedbacks and climate sensitivity have also been tested by assessing the response to large volcanic eruptions, such as Pinatubo (e.g. Wigley et al 2005). The model response and climate sensitivity is observed as predicted. http://www.realclimate.org/index.php/archives/2010/09/introduction-to-feedbacks/ http://www.skepticalscience.com/detailed-look-at-climate-sensitivity.html Wigley et al 2005: http://www.agu.org/pubs/crossref/2005/2004JD005557.shtml Water vapour has been observed to increase at 0.41 kg/m² per decade since 1988 (Santer et al 2007), corresponding to ~7%/degree C warming, in line with predictions. http://www.pnas.org/content/104/39/15248.full.pdf http://www.skepticalscience.com/water-vapor-greenhouse-gas-intermediate.htm Observed ice-albedo feedback in the Arctic: "Increasing solar heating of the Arctic Ocean and adjacent seas, 1979–2005: Attribution and role in the ice-albedo feedback" Perovich et al 2007 http://www.agu.org/pubs/crossref/2007/2007GL031480.shtml Positive feedbacks are real and observed, and all plausible estimates of climate sensitivity from palaeoclimate or models indicate a net positive feedback, ruling out clouds from preventing our current global warming. A thought-provoking review of a recent paper by Freudenburg and Muselli on the IPCC's underestimation of climate threats: "The Asymmetric War on Climate Change: No Cause for Alarmism?" http://www.skepticalscience.com/freudenburg.html "Asymmetry of Scientific Challenge is a theory that attempts to quantify bias in media reporting, and the effect it has on the science itself as well as public opinion. Freudenburg and Muselli 2010 examines this phenomena and finds that far from the predictions of climate science being exaggerated, there is a systematic bias that may diminish or conceal the true potential dangers we all face, and that this bias may seriously affect the work of bodies such as the IPCC." This supports the notion that the majority of recent research finds IPCC AR4 values underestimate changes or rates of change.

<br /><br /><br />Hi Jethro, how about in the IPCC AR4 report here: http://www.ipcc.ch/publications_and_data/ar4/wg1/en/tssts-4-1.html Without CO2, ocean temps are ~0.5C lower, land temps are ~0.8C lower than with CO2. So Arctic ice should, without anthropogenic CO2, perhaps be approximately where it was at the beginning of the century, the last time global temps were that low, when it took multiple years to traverse either the NWP or the Northeast Passage. Now you can do both in a single season. If the increased solar forcing since the beginning of the century has a disproportionately large effect on Arctic ice, then perhaps it would be comparable to the 1940s-1950s extents, still far higher than today's, and only a little less than at the start of the century.

Jethro, it's James Delingpole... are you remotely surprised? But meanwhile we're still on track for one of the warmest, if not the warmest year on record. Funny how people keep crying about global cooling when it's still warming and has been warming for decades. mycroft, I was talking about the future (2C), not the past, in the context of 2C rise being a conservative prediction of warming due to double CO2. And do you understand the difference between adding/removing energy from the climate system, and adding/removing energy just from the oceans? The oceans are part of the climate system and can, of course, gain heat from or lose heat to other parts of the climate system. They cannot create their own heat, and if they lose heat, it goes somewhere else in the climate system, it doesn't magically vanish. Skeptics suggest that the ocean 'cycles' are driving warming, yet the heat content in the oceans is steadily rising, and the top-of-the-atmosphere energy balance is positive (ie at the place where energy arrives and leaves the climate system, more energy is arriving than leaving). Coincidentally, this energy is being trapped at the absorbtion wavelengths of the CO2 molecule... http://www.skepticalscience.com/global-warming-stopped-in-1998-intermediate.htm We're also back to the predictive question - why do you think climate forecasting should be chaotic? Is it because you're thinking of it as a glorified weather forecast? It is a boundary condition problem, much like the difference between forecasting the weather in 10 days time being compared to forecasting the weather in January. You'll have a large range in each, driven by synoptic patterns, but held within two boundaries for each forecast. But you could put good money on the January weather being colder on average. The boundaries in climate forecasting are primarily determined by ENSO, volcanic, solar, aerosols and GHG values. ENSO drives a lot of the interannual variability, but the upward trend of CO2 means that each decade's worth of interannual variability is warmer than the last decade. It's exactly the reason why you can't base a climate trend on a few years of data, just as you can't identify the trend between seasons on a week's worth of weather. 97% of climate scientists figure comes from two recent papers: Doran 2009 and Anderegg 2010: http://www.skepticalscience.com/global-warming-scientific-consensus-intermediate.htm Observation, replication, prediction... Warming due to GHGs has been predicted repeatedly for most of the last century, and is now observed directly by independent means. Observations are consistent with predictions. Observations of warming and of the causes of warming have been replicated by numerous independent studies with different methodologies. In fact, more so than most other disciplines due to the sensitivity of the subject! http://www.ncdc.noaa.gov/bams-state-of-the-climate/2009.php Y.S., if clouds are the global saviour, how do you explain past climate variations, which demonstrably operated with positive feedbacks, or more specifically, why would clouds moderate temperatures in the present day when they have not moderated temperatures for any past climate change, given that observed changes are larger than the forcings that drive them? You should read: http://www.realclimate.org/index.php/archives/2010/09/introduction-to-feedbacks/ Also: http://www.skepticalscience.com/Pacific-Decadal-Oscillation-intermediate.htm Or do you think that cloud moderation is only applicable for the modern human-induced warming? Ocean oscillation (PDO, AMO) show no overall trend, but the same ocean basins (and global oceans) are warming... because in order to highlight the oscillation data, the warming trend has been removed. Something newsworthy, the quite shocking scale of Wegman's bias, plagiarism and distortion has been collected and published in a single document by John Mashey. The report that pretended to be an independent review of Mann's hockey stick and of climate science quite blatantly wasn't in the least bit impartial or professional: Executive summary: http://deepclimate.files.wordpress.com/2010/09/strange-scholarship-v1-0-exec.pdf Full report and description of the background here: http://deepclimate.org/2010/09/26/strange-scholarship-wegman-report/ The Wegman report is evidentially not a reliable source of information for anything to do with climate science.

Given that oceanographers, particularly those that collect and study marine sediment cores (and I count more than a few as friends) would consider themselves palaeoclimatologists (kind of back to VP's set theory in a way!), and also consider themselves climate scientists, I don't see what your point is. weather eater's excellent point about who is responsible for our understanding of natural cycles is worth thinking about - it is palaeoclimatologists. Why would it be it that the very people who discovered and analysed the various natural cycles present in marine cores, ice cores, boreholes, tree rings and observational records would suddenly not understand their own science? How would the natural oceanographic cycles, which are incapable of creating energy, drive an energy imbalance at the top of the atmosphere? Most medium-term natural variations (ie sub-Milankovitch but super-decadal and pre-20th Century changes in the total heat content of the Earth) appear to be solar and volcanic in origin, while the oceans just push the energy around a bit... in line with the oceans' inability to add or remove energy from the climate system. Can you name respected palaeoclimatologists or oceanographers with relevant research experience who don't accept AGW theory? 97% of publishing climate scientists accept AGW, so I imagine dissenting oceanographers are rather thin on the ground... On the emails dead horse... if someone was harassing you maliciously (e.g. MacIntytre to CRU), would you or would you not think poorly of them when discussing them in private? Seriously? As you say, the focus of current research has moved on from questions of "is it warming?" (it is) and "is anthropogenic CO2 culpable?" (it is) to "What is the climate sensitivity?" Climate sensitivity lies between about 2C and 4.5C per doubling (Knutti and Hegerl and many others) per doubling of CO2. Figures below ~2C are incapable of explaining past climate variations and do not hold much scientific merit anymore. So... do you think a globally averaged warming of 2C, with localised warmings of much more than that, as well as associated more intense heatwaves and floods,mass loss of ocean life caused by acidification, and with an associated sea level rise measured in metres is nothing to worry about? "No one has been dragged anywhere by the evidence"? Do you really stand by that statement? I'd be interested to understand your philosophy on the application of the scientific method, perhaps in line with weather eater's request for your convincing counter-theory to AGW? :hi:

Hi barrel, you're right to be cautious about anything you might read, whatever the source. It's the first step in true scientific critical thinking, to evaluate the evidence rather than simply believing what someone says, and that of course includes anything I might say! But you're being hard on the IPCC, as the very few errors that have been identified in the report are inconsequential to the key findings of the report, and a number of supposed errors raised by skeptics have turned out on inspection not to be erroneous. You can verify that for yourself by reading the report and tracking down the evidence upon which it is based. The core message of the IPCC findings, that of human-caused emissions causing global warming is not in question. Clearly the nature of some of the minor errors found should hopefully lead to improved practices to further eliminate the existence of even these minor errors. On CO2, your statement 'C' is the correct one, in that it is the only one that can explain past climate changes such as snowball/hothouse earth oscillations, the amplification of the Milankovitch orbital variations into Quaternary glacial/interglacial cycles, or the present rapid warming. When temperature leads, CO2 follows as its solubility in ocean water is reduced, and the released CO2 amplifies the temperature rise. When CO2 leads (such as the snowball to hothouse Earth transition or modern industrial CO2 emissions), the fundamental physical properties of the CO2 molecule, namely that it absorbs and scatters outgoing longwave radiation, means the Earth must warm, driving further CO2 release. Clearly the two must operate together - CO2 release causes temperature rise, which causes further CO2 release causing a further temperature rise and so on, regardless of which is the initial trigger. This does not lead to a runaway warming because the feedback 'gain' is less than 1 - each subsequent feedback warming is smaller than the last, leading to a converging series and a temperature and CO2 concentration that is higher by some amount than the initial change. Most climate researchers understand the bigger picture in a far more sophisticated manner than they are given credit for. Publication on one detailed branch of the science requires a sound understanding of the other related sciences and their interrelationships. It is one reason why skeptics come unstuck so regularly - they lack this knowledge of how to piece everything together. They concentrate on one single cherry and come to the wrong conclusion based on that cherry because they miss the larger web of interrelated supporting evidence that resoundingly disproves their take on the 'cherry'. The 'three blind men asked to describe an elephant' analogy is neat here - one thinks it's a snake, another a boulder, a third a tree trunk... they're each wrong, because they only see a small part of the picture and interpret it wrongly to boot. The same goes for skeptics' interpretations of hockey sticks (of which there are now very many, and more appearing all the time), global temperature rises, CO2 effects, or climate sensitivity. Climate science requires you to evaluate a broad range of evidence which, when combined, points to a single, compelling conclusion, but which cannot be arrived at from one single direction. Of course whether you accept this does depend on the evidence, not just that I (or anyone else) said so - below is a small part of the evidence I accept to help form an opinion of how the climate system works. It all forms a far more coherent and complete picture of the climate system, via physical theory and supporting observations, than any explanations forthcoming from climate skeptics. More on CO2: http://www.aip.org/h...climate/co2.htm http://www.skeptical...ivity-basic.htm (Basic, Intermediate and Advanced versions available) http://www.skeptical...on-response.pdf (The 'Climate Scientists Respond' submission to Congress) Much more on feedbacks: http://www.realclima...n-to-feedbacks/ On glaciers, you can refer to the World Glacier Monitoring Service (http://www.geo.uzh.ch/wgms/) for more information, and summarised at Skeptical Science here: http://www.skeptical...ers-growing.htm (Basic and Intermediate versions available) The vast majority of glaciers are retreating, and they are absolutely not counterbalanced by advancing glaciers. In case you were thinking of Antarctic sea ice, which has increased slightly, there is more information here: http://www.skeptical...gaining-ice.htm Sea ice should not be confused with land ice, one of which will raise sea levels, the other does not. Attached are some pretty pictures of glacier retreat from some of my favourite glaciers in Iceland - Gigjokull, Solheimajokull and Steinsholtsjokull. Each pair is an image from 2002 and 2010 showing eight years of retreat, and images are from approximately, but not exactly, the same location. The Steinsholtsjokull images are pretty close in that respect. You can see landmarks in each image to gauge the retreats. The upper parts of Gigjokull has been affected dramatically by this year's eruption of Eyjafjallajokull and the attendant jokulhlaups, but the size and position of the snout in this year's image is similar to last year, and the retreat over the past decade is not volcanic in origin. The other glaciers have also been unaffected by volcanic activity. On a side note, Gigjokull is essentially doomed from now because it has lost such a large chunk of its accumulation area that it will now retreat rapidly and take decades to start regrowing to even a shadow of its former self. The Icelandic retreats are in line with the WGMS data showing nearly all glaciers in accelerating retreat around the world.

Indeed it is, from watts the weatherman, disinformer-in-chief over the pond. Accusing others of misusing data! McShane and Wyner have attracted not one, but two rebuttals for their garbage paper: http://www.people.fas.harvard.edu/~tingley/Blakeley_Discussion_Tingley_Submitted.pdf "Within the paleoclimate context, where the expectation is that each proxy is weakly correlated to the northern hemisphere mean (for two reasons: proxies generally have a weak correlation with local climate, which in turn is weakly correlated with a hemispheric average) the LASSO as used by MW2010 is simply not an appropriate tool. It throws away too much information." http://pubs.giss.nasa.gov/docs/notyet/inpress_Schmidt_etal_2.pdf "Assessing the skill of methods that do not work well (such as Lasso) and concluding that no method can therefore work well, is logically flawed. Additional problems exist in their assessment procedure – reducing the size of the hold out periods to 30 years from 46 years in M08, for instance, makes it more difficult to meaningfully diagnose statistical skill." So the McShane and Wyner paper that attempted to claim to disprove the whole of palaeoclimate science by using dodgy statistics is, in the words of the Cat from Red Dwarf, deader than corduroy. Not surprisingly of course, it has gone the way of other such papers, like McLean et al, that somehow make it past the review process, only to be publicly eviscerated by rebuttals. Of course, people like Watts gullibly, or deliberately, report on them as if they have rewritten the science. Sadly Watts has shown far too many times he does not know what he is talking about, and will happily repost anything contrary or misleading about the science of climate change, be it steven goddard's perpetual nonsense on the cryosphere, or Monckton's inane rantings. And he has the cheek to claim others' data analysis is flawed! Speaking of Monckton, some other news - he's had his rear handed to him by a large group of climate scientists regarding his false testimony to Congress: http://www.skepticalscience.com/Monckton-response.pdf http://www.skepticalscience.com/Climate-scientists-respond-to-Moncktons-misinformation.html Some of Monckton's arguments have been used by people here, so the report for Congress is worth a read! The disinformation movement succeds in that it forced hard-working professional climate scientists in a variety of fields to devote time to debunk yet more garbage, rather than pushing on with the science. Another interesting read here: http://www.skepticalscience.com/billions-of-blow-dryers.html http://www.pmel.noaa.gov/people/gjohnson/Recent_AABW_Warming_v3.pdf ...though maybe for 'new research' - looks like some of the missing heat from Earth's energy budget is reporting in - from the deep oceans, specifically warming of Antarctic Bottom Water.

Which research, Jethro? The '07 IPCC has underestimated sea level rise by a lot according to a number of subsequent papers, one of which was retracted because its estimates were too small. But maybe there's even newer research you can link to? As for implications of the continued reduction in Arctic ice extent, look no further than the increasing amount of absorbtion of energy by dark ocean water as compared to reflection by white ice. This is most likely the cause of Greenland's observed accelerating ice loss, which will of course affect sea levels. http://climatecrocks...sea-ice-update/ Funny how some are taking (rather desperate) solace in our shortest melt season in the IJIS record. It is indeed the shortest melt season, and the minimum would have to be on or after the 29th September for it to be anything otherwise. This has been known since 1st April (fool's day?), because it was entirely due to the remarkable late end to the winter season that this particular record has occurred. 2010 was the latest end of the freeze-up by 10 days from 2003, and by at least 20 days from any other year in IJIS data. But of course we know that was all thin new ice that hardly lasted the following month. 2010 has the third-greatest loss in extent in the IJIS record, and could yet catch 2007. It has, of course, no more than the third-lowest extent in the IJIS record, most similar to 2008 in extent, though so far the curve has a late-season shape similar to 2007, and it will be interesting to see where and when it bottoms out. Area, according to the IJIS data is essentially a tie for 2nd place with 2008. Volume, according to PIOMAS, continues its slide, with a September volume close to 3,900km^3. This compares to 6,600km^3 in 2008 and 9,800km^3 in 2006. I'll leave it to others to calculate when zero is passed at that rate... Certainly no "recovery" this year, not that the professionals are in the lest bit surprised. It's just a few amateurs and misinformers that continue to predict cooling (as they have done for years without any success), while the Earth records successions of record high temperatures and a strong accelerating trend of less Arctic ice. Why do people try and predict cooling, which is always going to happen some time after the current date, when all the observations show warming to present, in line with the observed and predicted mechanisms? 2010 in relation to previous NSIDC and IJIS years, and the quadratic trend through 1979-2009 NSIDC data. Projections for further losses in line with the three years with end dates on or after 17th Sept also shown (2003,2005,2007). And 2010's still not necessarily finished yet, as NDS's excellent posts show!

Indeed, very interesting too. I've read somewhere about the possibility of August end of melt dates, but looking at the state of the ice across the basin, I somehow doubt that is what we're seeing here. On average, IJIS extents lose 250,000sq km from now to melt season end. But will this be an average year?

Two excellent points. If we can actually have some corroborated evidence of cloud cover changes driving temperature, then there would be something interesting to talk about. It is interesting how some people repeat falsehoods about Mann and Hansen and others despite exonerations (I think, by now, their methods are the most public of all!). Spencer hasn't had any enquiries go after him because to date his cloud results haven't been that important, or very good. Jethro, you're right about clouds being highlighted by the IPCC - they are of course crucial, and your excerpt shows this is not a topic the scientific community are ducking. But holding a senior position and having awards etc does not give you a free ride to the truth - you are still judged on the quality of what you produce. On that score (to use the above examples), to date Hansen and Mann have scored much more highly than Spencer, despite blogosphere attempts to muddy reputations. If Spencer comes up with the goods and shows the necessary changes in cloud cover, then all well and good, but so far he hasn't. Why are people so quick to accept the word of Spencer, yet equally quick to dismiss the results of thousands of other scientists that happen to point to a single alternative conclusion?

I love the accusations of entrenched views.... from people with utterly entrenched views! The dismissal of ample evidence for an Arctic that is now warmer than it has been in ~3,000 years from glacier ice melt (time integrated Y.S., takes more than a few warm years), or ice shelf collapse, or open water limits on NE Greenland, or other proxy evidence such as that described in Polyak et al 2010. And why is the evidence dismissed? Oh yes, because of a few Norse finds in the Baffin Island area and inland, that could quite reasonably have arrived by trade to the eastern margins and by futher trade within Inuit communities further west. Somehow that is suddenly translated into "NWP probably open a lot between 900-1400AD". And of course Greenland was, by some logic on here, totally uninhabitable at any conditions cooler than today (despite continuous Inuit presence)... Very clearly, blog science is a different beast from real science . You don't dismiss evidence because it does not fit into your worldviews, but if the Arctic was warmer, or even as warm, as present during the MWP, how can you explain the physical evidence that says it wasn't? Norse artifacts are much easier to explain in the context of an Arctic cooler than present but warmer than the LIA. Melted glaciers, collapsed ice shelves, open water limits and other proxy evidence all pointing to conditions not seen in several thousand years is much harder to explain with a warm Medieval Arctic. But if you want to keep dismissing that evidence and cry 'conspiracy'... carry on...

You can't go around making up claims about "lots of anecdotal evidence the passage was open" without providing some of the evidence. Clearly there isn't lots of evidence, otherwise you might have provided some. I think people get rather hung up on a concept that conditions warmer than the Little Ice Age somehow must always mean that those conditions equalled today's warmth. You see this with those suggesting the reports of unusual warmth in the Arctic in the 1920s... was warm compared to 1870, but actually very cold compared to the present day. Similarly, today's conditions have not been equalled for several thousand years, as shown by multiple independent lines of evidence (proxies, fossils, shorelines, glaciers, ice shelves), indicating that those conditions were not met in the Medieval Warm Period. The MWP was quite pronounced in Greenland, compared to the Little Ice Age, but compared to today's coditions, it was clearly cooler in the Arctic then than now. Conditions in the 1980s were distinctly warm in the Arctic compared to the Little Ice Age. Yet the NWP was never open... EDIT: And papers published in Science hardly qualify as 'obscure reports'...

So Spencer still believes that scientists are naughty and he's repeating debunked rubbish in suggesting there was any substance to the climategate allegations. Of course all the subsequent exonerations by multiple independent panels mean nothing... Other cloud research has not shown the same links Spencer claims, so it seems he's the one out on a limb, and with a track record of producing ropey results. I'd still be intersted to know how, if clouds are such a powerful negative feedback, we get large palaeoclimatic shifts from small initial orbital forcings. CO2 explains that well, quite apart from all the other direct evidence for CO2 operating as expected today... Lets see what the professionals have to say, if they care a jot about Spencer's claims these days. The last few times out Spencer's claims were torn to shreds, so I hope he's got his sums, and graphs, in order and not cooked up this time.

Quite where are the suggestions of the NWP open for decades in the summer, stewfox? Reliable sources? I don't see such a claim being made on your link to Scott Mandia's excellent blog (the blog is well worth taking the time to peruse), especially the "Global warming: man or myth?" section: http://www2.sunysuffolk.edu/mandias/global_warming/ G-W and NDS - Patrick Lockerby, who first reported the calving event, reckons the Petermann Ice Island is not likely to remain intact, and I'd agree that it would be surprising to see it remain in one piece for long. It's quite thin as glacier termini go as well, so much will depend on how deep the water is in the main Nares Strait. It will certainly be interesting to watch! http://www.science20.com/chatter_box/petermann_ice_island_revisited_0 P.P. - you're right, it indicates the layer was probably not there 4,000 years ago, but also that it has been there ever since (and was clearly there at sampling time). Is the snowpatch melting out now? That would be consistent with the other ice indicators - the ice shelves and small ice caps revealing 3,000 year old surfaces. I won't answer your second question!

Hope it's better than Spencer and Braswell's last effort.... http://www.realclima...e-easy-lessons/ The section on Spencer's rather bizarre "internal radiative forcing" [weather] is worth a re-read as that concept rears it's head again in Spencer's new paper. I'll await the professional responses to this paper, but I wonder if Spencer has the wrong end of the stick (yet) again? Also worth noting is that the feedbacks are a product of the physics in the models, not specifically coded in - from the above RealClimate post: "the concept of feedbacks is just something used to try to make sense of what a model does, and does not actually enter into the formulation of the model itself." Spencer's unfounded accusations against climate modellers do him no favours in the world of real science, and his failure to understand where the feedbacks come from gives me rather serious concerns about the validity of his latest paper. Some might have already made their minds up about the validity of the paper, but I'd prefer to see some independent corroboration, and see how it stands up to criticism.

http://www.cgd.ucar....eaiceArctic.pdf Polyak et al (2010) History of sea ice in the Arctic. You'll see linked within references to the best available measures of Arctic sea ice during the Holocene and recent times, including the last 140 years. Figure 2 from a linked paper, Kinnard et al (2008), is reproduced below: You'll see how it's quite reasonable to consider the 1920s rather warmer/slightly less ice in the Arctic than the 1870s; however both periods have much more ice than during the past three decades of rapid and sustained decline. Someone writing in the 1920s might think it unusually warm, but we would consider those same conditions remarkably cold by today's standards. And >7-8million sq km, depending on your extent measure, is absolutely reasonable for all years in the record prior to 1980. Just because it's not a satellite dataset does not invalidate it from being a decent dataset. It certainly beats cherry-picking out-of-context observation logs! You'll also see various independent lines of evidence pointing to the Arctic not having been in a similar state for several thousand years. I would add to them ice cap retreat and ice shelf collapse indicating conditions not met for >3000 years. Do you have anything better? The 'insult to the memories' is a reference to the fact that a great many brave people struggled to find routes through the Arctic waters during the whole of the 19th Century. Some people (not necessarily on here) like to try and belittle that fact in a vain attempt to pretend that somehow the Arctic was actually like it is now at times during that century. Do you seriously think the explorers would have the same problems locating passages today? When a sailing boat has a decent chance of sailing both the Northeast Passage (completed) and the Northwest Passage in a single season?

Joe B also has a habit of being woefully wrong.... There's always some wag predicting cooling, but never any evidence of global cooling! A bit like there's always someone predicting the end of the world

The figures were September's, so minimum annual extent. I think the other monthly figures are readily available from NSIDC, and data from further back can be extracted from the papers I linked to. In general, I think it's a bit of a fool's errand to try and fit cycles of this kind of magnitude to sea ice extents, when there is no evidence of minimum extents prior to the 1970s much less than the map of 1930s extents I linked to previously. The evidence for relative warmth 1920-1940 contains no indication of extent reductions approaching anywhere near recent values, and extents would appear to have remained above the 7-8million sq km. Therefore, if there is a cyclical component, the variation in overall Arctic ice extent is small. The present reduction has no apparent cyclical component. The concept of conditions with a reduction of ice comparable to present existing during the 19th Century is almost an insult to the memories of people who died in the search for the Northwest Passage, often spending multiple years locked in the pack attempting to get through. Now you can sail the Passage in a relatively flimsy boat every year, including this year.

mycroft that wasn't directed at you! stewfox, what about the trends in warm or cold records? Or the areas of the globe affected by the warm/cold anomalies? Of course weather can set records anytime, but we see more and more warm records w.r.t. cold records being broken...

Hi Jethro, I agree with you - this study is indeed good news, if verified. I'd certainly be happier in a world where the ice caps were shrinking at a slower rate. I think such a revision would still have us at the high end of current IPCC sea level projections (given that they have been seen as too low by most recent studies), and is not an excuse for us to delay action, but it might give us more time to avoid the worst effects of warming.

Is this what you were after VP? I fitted the quadratic to the NSIDC Sept data 1979-2009, similar to what Tamino did in a recent post. Clearly as you back-cast the relationship will break down. For a forecast, much will depend on whether the accelerating trend accelerates to zero, or whether it takes a logistic curve form and flattens off as zero is approached. The latter form assumes that there are some regions where it is very difficult to melt out all the ice. Both forms of course assume continued Arctic warming!

I'm not sure what you're driving at here VP - you seem to have more assumptions in your model that can really be considered with the data? You can't really assume a sinusoid in 'natural variability' of the Arctic as determined by sea ice. There is no obvious 'low' in Arctic ice around 1922 - the passage you refer to merely indicates that the conditions that year were warmer than years before 1922 and, as NDS says, are not inconsistent with the 1930s sea ice minimum map. There is, however, an obvious decline in sea ice starting somewhere around the 1970s. A sinusoid-plus-trend fitting of a figure like the one above has the trend utterly dominating as you head towards recent years? And you'd be making an awfully large assumption to suggest we have bottomed out on the recend downward trend?

Interesting weekend for ice extent on IJIS. Two large drops - one of them the second-latest 70,000sq km drop in the IJIS record, followed by the first gain (provisionally) of the season. It's important to note that today's rise is provisional as every day the IJIS figures are revised once, sometimes upwards, sometimes downwards, entirely normal practice for IJIS. A rise at this stage is not unprecedented, and we still expect losses totalling on average ~300,000sq km before the end of the melt season. This places us squarely between 2008 and 2009, and we are now virtually certain to finish below 2009's extent. Red triangles indicated projected end dates and values based on melt from the current value at the extent loss rates of each previous year. The average projected endpoint is a whisker above 5,000,000sq km. Weather will most likely be the key driver of the timing of the end date and the amount lost before the end of the season - three interesting "end zone" articles at Neven's blog on that: http://neven1.typepad.com/blog/ CJWRC, note that different organisations use differnt measaures of extent, so comparing values from two different measures is not worthwhile. The NORSEX graph you pointed to shows almost exactly the same story as IJIS - that 2010 is going to finish between 2009 and 2008 - but it has different numbers on the Y-axis. Extent is an odd measure in that it is neither area nor volume, and until we have reliable volume measures, it is what we have to use. But it can hide a lot of ice gain or loss within its parameters.

Is there a suggestion that there shouldn't be a debate at all unless you agree with a certain point of view? Interesting view for posting on a forum! I agree with you mycroft in that I think Pachauri probably does have grounds for libel against North, and I wonder how long it will be before people like North or Monckton draw libel suits against themselves, given the continuous barrage of blatantly false accusations coming from those quarters. Certainly the trend appears to be towards retraction of the false stories and apologies, indicating that where these issues are considered at a legal level, the spreaders of disinformation in the print media are not considered to be in the right.

Every variation has to have a cause - whether 'natural' or not. Appealing to an unquantified natural variation, when we have a cause with all the relevant physical and direct observational evidence to support it (no I'm not talking about heatwaves or floods) seems irrational to me. Many natural variations are quantified - they are just smaller/show no trend w.r.t. GHGs. In the news today - the Telegraph has for a second time in recent months had to print an apology for printing denialist misinformation, this time about Rajendra Pachauri: http://www.guardian....l-relationships http://climateprogre...aph-apologizes/ Pachauri was accused by various people, including usual suspects Booker and North of the Telegraph, of financially abusing his position as head of the IPCC. To clear his name, an audit of accounts was done by KPMG, which not only found Pachauri to have not gained from his position, he's refused financial rewards entitled to him! And he receives nothing for being head of IPCC either. And yet the lying journalist North who started the whole fuss continues to make the same false statements after being shown to be wrong (see Monbiot's article)... Once again, the trouble is that the initial lies have spread further and will be read and believed by many more people than the subsequent retraction and apology. And once again, the deniers show that they haven't the skill to attack the science, so they attack the messengers...