songster

Precisely. The global climate appears to have several quasi-stable states. Off the top of my head, I can list at least four: snowball Earth, Ice Age, temperate interglacial and hothouse. These respectively have: total ice cover, large ice caps, small ice caps, no ice caps. Currently we are in the temperate interglacial state. Any or all of the above climates (except maybe snowball Earth) are likely to be compatible with human life and advanced civilisation. The process of changing from one state to another is very likely to disrupt human civilisation and may even cause a complete breakdown back to hunter-gatherer levels. As such, we really should do all we can to avoid pushing ourselves towards the tipping points that cause climate transitions. Since the details of these are unknown, extreme caution in adding or removing any particular forcing (e.g. GHGs, deforestation) is advisable.

For those perplexed by the above link, the word "b a s t a r d i" (without spaces) has been converted to "laminate floori" by some particularly dense profanity filter.

You're reading the graph wrong. It's not a measure of absolute volume, it's a measure of the volume anomaly, i.e. how much more/less ice there is than average for the time of year. In September 2007, there was about 8000 km3 less ice than the September average. Currently, we have about 8000 km3 less than the May average.

Rather than trying to count the inputs and outputs based on an large number of unknowns, isn't it far simpler to look at the total size of the reservoir? Grass is shorter than a tree, this much is obvious. If you replace <i>n</i> acres of trees with <i>n</i> acres of grass, all the carbon that used to be in the trees has to go somewhere. Unless all the wood got made into buildings (and preserved with Neolithic anti-rot treatments?), that carbon ended up in the atmosphere. Possibly even more carbon was released, depending on whether forest soils are thicker/deeper reservoirs than grassland soils.

Time for a summer ice melt thread yet?

What's your explanation for the observation that ice area is also recovering over the last two years? Ice area calculations weight the data on a per-pixel basis, so a 15% pixel counts as 0.15, a 50% pixel counts as 0.5, etc.

Sorry, but no. Ice area and extent were both improved in '09 relative to '08 and '08 relative to '07. Ice area is weighted on a per-pixel according to the percentage cover, so it should be less affected by the "spreading out" effect. I'm quite willing to believe the pack was in bad shape - fragmented, leads etc. However it's just not true that it was sparse enough to give a misleading picture of extent or area. Look at the pictures from August/September last year - the large majority is at >= 95% concentration. http://igloo.atmos.uiuc.edu/cgi-bin/test/print.sh?fm=08&fd=30&fy=2009&sm=09&sd=10&sy=2009

There you have it. You're focusing on the first half of the sentence, and Gray-Wolf is focusing on the second half. Time will tell which is the correct view. Key questions that need answers are: Does second/third year ice really qualify as "multi-year", or is it only a little more resilient than first year ice? How old is the the really old stuff, the stuff that's continuing to decline? Five years, ten years, a century, a millennium? It's a well known fact that the Greenland ice cap is metastable - i.e. it exists because it exists. Its own altitude protects it from melting. If it were magically removed tonight, it could not and would not reform even if the climate got substantially colder. Does the same apply to the old perennial ice, i.e. the stuff that's decades or centuries old, not just 2-3 years? Will any of the current second/third year ice get the chance to become old perennial ice, or have we already lost the ocean conditions necessary for it to form?

Because humans are, by and large, a littoral species. The vast majority of our population, financial and industrial concentrations are on the shoreline, and will be inundated if there is any significant sea level rise. Also, our crop species are vast monocultures which we have tailored to very precisely fit the current climate. Even a small rise in temperature will affect their productivity. We have no way of knowing whether we will be able to adapt (say) wheat, rice and barley to grow in hotter and saltier soils. Yes, we can carry out selective breeding, but if the variation is not there in the first place we cannot select for it. Due to our intelligence, we are probably less vulnerable to climate change than most other species - we are unlikely to actually go extinct. Our civilisation, however, is uniquely vulnerable. You cannot just up sticks and migrate, when you're talking about moving (say) London. Significant sea level rise would drown our cities and industry, and send us back out to forage for a living. Along with that would come a vast reduction in population, from the 6.7 billion we can support with advanced agriculture, factory-produced fertilisers and industrial machinery, to the half-billion we can support with subsistence farming. In the worst-case scenario, if we lost wheat and rice as crop plants, that would send us back to pre-agricultural hunter-gatherer population levels, let alone pre-industrial - another factor of 10 or so. We'd be left searching for more heat-tolerant grass species to cultivate.

I asked a few pages back whether anyone had any hard data on what went wrong in late '06 and why there was such an abrupt stall in the re-freeze. The bigger concern is next summer. Did the stalled re-freeze in '06 precondition the ice pack for the record '07 losses? If so, what happens next year, with a stalled re-freeze this year and even less perennial to hold the fort?

Question looking at the IJIS figures - what the heck happened in 2006 from mid October through to end November? Was there anything unusual about the weather then, and did it somehow pre-condition the pack for the 2007 melt? Most importantly, how does that six-week period stack up to the predictions for the next few weeks?

That's not the case. The ice extent measurement treats any pixel with >15% ice concentration as being 100% covered with ice. The ice area measurement weights it according to the measured concentration. Let's illustrate it with a simple example data set. Say we have eight pixels in the data set, each one representing 100km^2. The concentrations for the eight pixels (sorted into order for convenience) are 10%, 10%, 20%, 50%, 80%, 85%, 90%, 95%. Extent calculation: Two pixels below 15% - treat as zero. Six pixels above 15% - treat as 100%. Stated ice extent = 600 km^2 Area calculation: Two pixels below 15% - treat as zero. Weight the other 6 pixels by percentage. (20%+50%+80%+85%+90%+95%) * 100km^2 = 420 km^2 This is why ice area figures are always lower than ice extent figures. The ratio of area to extent is equal to the average concentration across the pack as a whole - I've never actually seen the figure worked out, but it might be a handy measure of the degree of compaction of the pack. You could say that the area gives a better impression of the overall ice pack health, however as I said above it's susceptible to interference from melt ponding. Those pixels at 80/85/90/95% could all actually be 95% pixels with varying amounts of surface melt. Using extent instead will get round this issue at the cost of obscuring the effects of ice fragmentation. As long as you're consistent which you use, and the degree of fragmentation / ponding is similar from year to year, the overall trends will be accurate. Really, it's all an artefact of the problem that we don't have infinite resolution cameras. There's no such thing as "50% ice" in reality - a given point of the ocean surface is either iced over or not. Thing is, that's already taken care of in the area calculation. If you take a mass of 100% ice and spread it out so you now have twice as much 50% ice, then the ice extent measure will double, but the ice area measure will stay the same. The correction's already been done. Yes, the pack is a bit more compact this year than others (or possibly the melt ponds have iced over quicker). No, it's not sufficient to conclude that there's plenty of ice and the ongoing trend is all down to compaction. When you do the correction (i.e. use area rather than extent), it's still the third worst on record by quite some margin. Eyeballing pictures really isn't a good guide, unfortunately.

I'd be intrigued in the explanation too, because the original assertion is at best wishful thinking and at worst nonsense.. The monitoring sites generally use ice extent rather than area, because melt ponds on top of the ice can confound the data by looking like open water. Melt ponding is however extremely unlikely to drop the apparent coverage below 15%, so by using that as a threshold you get somewhat more stable results. However, area measurements (which adjust each pixel individually according to the measured concentration) are also available at Cryosphere Today. The graph is here. http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg As you can see, Arctic ice area (not extent) is currently having the third worst year since records began. Why someone would choose to spin that as "best concentration since 1979" is utterly beyond me, unless it's simply a case of looking at the bits where there is ice, and ignoring the bits where there isn't. I can play that game too by dropping an ice cube in the Pacific and saying "Look, this square centimetre is 100% covered in ice!" As to why the concentration appears higher this year than others, it could be winds compacting the pack and closing up leads, or it could be melt ponds icing over. My understanding is that it's been a colder and cloudier summer than usual up there, so the latter seems at least plausible.

Let's not prejudge that until we get a couple of weeks into July. The increased melt rate GW posted about a couple of days ago seems to be settling in, though we won't know for sure till the middle of the month. Currently it's faster than any year except 2007, meaning that the end-July level will end up somewhere between 2007 and 2008. If we then see the late August melt-out of the thin ice, we could be looking at a very low minimum.

Yeah, and if you extended the line we saw in the second week of June, we'd have ended the season with 10 km^2 of ice remaining. What does that have to do with the price of eggs? Extrapolating from a trend of a day or two isn't even Nostradamus-levels of scientific rigour <_< The next few weeks (not hours!) are of critical interest, since that will tell us whether we recapitulate the 2007 "cliff". After that, August will also be of great interest in terms of the continued melt-out of weak first-year ice.

Interesting. What's the location of the buoy like this year relative to last?

I know, which is why I tried hard to word it to make clear that I was using a generic "you" rather than a specific "you". Perhaps I should have written "One can spin it ... if one is so inclined", but then one would have sounded like the Queen. :-)

"Tracking" means bupkiss until a week or so into July. Pretty much all the lines are parallel to each other throughout the latter half of May and the whole of June. You (or GW, or I) can spin that any way you like, but the practical upshot is that the rate of daily melt through May/June gives us almost zero predictive information about the summer minimum. What matters this year are two things: 1) Will we see the rapid melt in late July, as in 2007? 2) Will we see prolonged melting througgout late August, as in 2008? Of these, the first seems to have been due to the "perfect storm" factors promoting summer melt, which are presumably unlikely to repeat. The second seems to have been due to the fact that there was vast amounts of first-year ice present which thinned through the summer and gave out in August. This is likely to repeat this year, given the ice pack makeup.

I'm sorry you took that inference from my post: I thought the phrase "NOT deliberately cherry-picked" was sufficiently unambiguous. They're not available in a daily format, however the monthly data is available - see links below. I recommend graphing the extent figures rather than the area figures for two reasons: (a) it will be more consistent with the IJIS figures, and ( if you graph extent, you have to decide what to do with the "polar hole". ftp://sidads.colorado.edu/DATASETS/NOAA/G...n/N_01_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...b/N_02_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...r/N_03_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...r/N_04_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...y/N_05_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...n/N_06_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...l/N_07_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...g/N_08_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...p/N_09_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...t/N_10_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...v/N_11_area.txt ftp://sidads.colorado.edu/DATASETS/NOAA/G...c/N_12_area.txt The full raw daily satellite data is also available linked from ftp://sidads.colorado.edu/pub/DATASETS/se...near-real-time/ - however in this case you need to have programs available to perform the extent calculation yourself (i.e. sum over the image and count all pixels >15% ice , with due regard to the projection from sphere to flat image). Certainly not something I personally know how to do! That is unfortunate, because it really obscures the wider picture. If anyone wants to claim there has been a recovery of Arctic ice towards the historical average, they need to know what that average is! Otherwise they're in the position of one who sees a redwood get cut down and gleefully cheers at the mushrooms growing on the stump. I intend no disrespect you personally in pointing this out, which is why I carefully said your graphs are not deliberately cherry-picked. However they do not tell anything like the full story, and it's important not to read any more into them than they will bear. The figures are supplied, at least on a monthly basis, and took me all of five minutes to find by following the links from the NSIDC front page.

It's informative to be sure, and it's not deliberately cherry-picked. However you need to be really cautious when looking only to the IJIS figures for evidence of recovery, since they only go back as far as 2000 - which means they cover the eight worst years on record! Values around the average of the IJIS data set are NOT a sustained recovery, they're evidence that things are still very bad indeed. For a more realistic comparison, you need to look at the figures on the NSIDC website, or on Cryosphere today, which will show you how the current ice pack is holding up relative to the 1979-2000 average. To save you the bother, I'll tell you today's figures: they're a million square kilometers lower than they should be. http://arctic.atmos.uiuc.edu/cryosphere/ http://nsidc.org/arcticseaicenews/ For what it's worth, my prediction for this year is "No better than 2008". We started the year with the same amount of ice as 2008, there's a similar proportion of first year / multi-year ice, and the conditions in 2008 were not particularly favourable or unfavourable for melt. Thus, if this year's conditions are similarly average, we should expect a similar melt. If we do tip into an El Nino and see greater melt earlier in the season, then the 2007 record is in danger. The truly worrying factor is that given an average melt season and average winter, 2008 saw no recovery in multi-year ice. We seem to have lost the conditions for creating it (and, more importantly, preventing it being flushed out by Arctic currents). Thus, for it to recover will require unusually cold winters, every year, for decades.

It's much too early to say anything. Look back at the IJIS plots for the last few years and see where the 2007 and 2008 melts broke away from the pack. Neither of them appeared out of the ordinary at this stage. 2007 broke away during July, due to extremely favourable conditions promoting the melt. It is reasonable to assume this will happen again if this year is similarly conducive to melt. If it's not, then as in 2008 the melt will appear comparatively unexceptional through June and July. 2008 didn't break away from the rest of the data curves until August. In this case the break away was due to "melting out" of vast amounts of thin first-year ice - thin because of the 2007 record melt. This meant that the melt season was prolonged well beyond the time when it normally tails off. It's important to point out that the thin first-year ice melted out even in what was a fairly normal year for melt conditions. Given that this summer has a similar proportion of first-year ice in place, it is reasonable to assume that this year will show a similarly prolonged melt season, with strong losses continuing through August. What does this mean for this thread? It means there's very little point faffing around pointing at individual days' results! By mid-July it will be clear whether we're following the "normal" 2000-2006 pattern or the catastrophic 2007 pattern. And we won't know until mid-August whether the extreme late-season melt of 2008 will repeat itself. If both these potential disasters are evaded, we could see a return to ~2005 levels of ice (still well down from the 70s and 80s!). If either comes to pass, we'll be looking at another very bad year, while if both come to pass, we'll see a new record low.

Correct in that increase / decrease in the area of ice outside the arctic basin is unlikely to have a large effect on the recovery of ice thickness in the central arctic. Just plot the numbers if you don't believe me - e.g. a scatter plot with each winter's maximum area on the X axis and the following summer's minimum area on the Y axis. There's only a weak relation. To get a recovery of summer ice coverage in the central arctic, what you need is for more ice to be retained during summer, so that it thickens into multi-year ice and is thus more resistant to the summer melt. It needs to be sustained over many years, to match the massive loss of multi-year ice over the last 20 years. It's a positive feedback loop that can go either way - right now we're spiralling down and may have passed a point of no return.

Not really. Looking back over the IJIS record, there really is very little variation in the May 31st figure from one year to the next, and the May 31st figure is not correlated with the September minimum. The May figure marks the transition between fringe melt and central melt, that's all, We had extra melt during May because there was more fringe ice to get rid of, that's all.

May/June border is when IJIS shifts from their "winter" ice calculation algorithm to the summer algorithm. I don't know the details of the difference between the two, but I know that the reason two different algorithms are needed is because in summer there are melt ponds on top of the ice that can appear as open water. If they did not correct for this, then summer totals would look much lower. The reason for the "blip", and why it's present in some years but not others, presumably has to to with the varying percentage of cracked ice, open leads and melt ponds from season to season. In regard to the last dozen pages or so, all I can say is that the current ice extent is totally irrelevant. If you look at the IJIS data, the May levels are simply not correlated with the September levels to any meaningful extent. This is because the April -> June melt involves the "fringe" of ice outside the main Arctic basin, while the June - August melt involves the central ice. Fringe ice forms and melts between mid-November and end-May, while central ice melts and reforms between start-June and mid-November. There's comparatively little connection between the two: look how little variation there is between years at the "transition points" (end-May or mid-November), compared to the inter-year variability in March or August. Thus far this season, all we have been observing is the dynamics of the fringe - which will be totally melted out within the next month or so regardless of Arctic conditions. Almost all the extra ice which is being held up as some sort of "recovery" is in the Barents sea. It has no bearing on the central melt, the Barents is always 100% ice-free by the end of the summer. It's a local phenomenon. As it melts out the IJIS measurements will inevitably trend downwards again relative to previous years.

What on Earth are you on about? They're being airlifted out because the ice is cracking up under them. The average ice thickness for their whole journey was under two meters. http://news.bbc.co.uk/2/hi/science/nature/8049563.stm