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Lennartvdl
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"What kind of chicken did we have in the oven?" That indeed seems to be the question. How frozen was it? How warm will the oven stay for how long, this year? Will the Arctic suprise us yet again?
Toggle Commented Jun 30, 2014 on ASI 2014 update 4: high times at Arctic Sea Ice
The NASA-post being picked-up: http://www.livescience.com/46264-greenland-glacier-loses-ice-photo.html
So far this year it seems to have been on average about 7 degrees C warmer than normal in the Arctic: http://ocean.dmi.dk/arctic/meant80n.uk.php Ice extent is at about the record minimum for this time of the year. And spring is in the air. At least here in Holland it is, where so far this winter we've had no full day below zero degrees C, for the first time ever. Average Holland temperature this winter (extended fall) has been second highest so far (only 2007 had a higher average). Let's see how fast the Northern hemisphere snow cover will melt this spring.
Arctic Report Card 2013 press conference at AGU Fall Meeting: http://www.youtube.com/watch?v=dZZsTgl-jHQ
SH, Nicely put. The strength of positive and negative feedbacks will determine the outcome, together with the GHG-forcing. And it seems we all do not know enough about how the ice caps will respond to this kind of forcing. GIS also seems to have two glacier fjords which extend deep into the interior of the ice cap, at Jakobshavn and Petermann glaciers. So although WAIS seems more unstable than GIS, this may be a pretty vulnerable ice sheet as well.
Toggle Commented Oct 3, 2013 on Pinpointing the minimum at Arctic Sea Ice
"Even more than doubling the current average melt rate to 400KM3/year we are still looking at a minimum of 700 years for the cap to melt out." You mean 7000 years, I suppose. Then again, over the past three years GIS lost about 400 km3/yr on average. Let's say this will continue until 2020. And then could this double in another 20 years to 800 km3/yr from 2020-2040? And then again to 1600 km3/yr from 2040-2060, and again to 3200 km3/yr from 2060-2080? Then the rate would be about 9 mm/yr of SLR contribution from GIS. If that rate could be sustained, with positive and negative feedbacks about in balance, then it would take about 700 years for near melt-out of GIS. I don't know if this is possible. And the risks for Antarctica seem higher. But scientists like Jim Hansen do suspect such accelerations could be possible under BAU. So I think it's too early to completely dismiss such scenarios.
Toggle Commented Oct 2, 2013 on Pinpointing the minimum at Arctic Sea Ice
Peter, We're all wondering the same. Part of the scientists seems to think it will take at least a thousand years. Another part seems to fear it may take as little as three or four centuries, if we continue with BAU.
Toggle Commented Oct 1, 2013 on Pinpointing the minimum at Arctic Sea Ice
Was it 40 cm of ice, or snow? Or a combination?
The Colbert Report reported on 'the lake at the North Pole': http://www.colbertnation.com/the-colbert-report-videos/428206/july-30-2013/smokin--pole---the-quest-for-arctic-riches--north-pole-lake
Look at figures 3, 4 and 5 in Bamber et al 2013, as linked above earlier: http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf On pp.506-507 they say, as also cited above: “In the Jakobshavn catchment, there is a dendritic channel system extending for about 325 km from the current grounding line into the interior almost as far as the ice divide. It seems likely that this is a palaeo-fluvial feature that predates ice cover in Greenland and may be important for subglacial water routing… The width of the trough is 3–4 km and the region of fastest flow coincides fairly well with the location of the deepest ice. The trough is 1366m below sea level at its deepest point compared to a maximum depth over the entire region of 556m below sea level in the older dataset. The main trough of Jakobshavn Isbrae is not continuous in the new dataset, disappearing around 100 km and reappearing at about 140 km. This does not imply that the trough is discontinuous, but only that there are insufficient data to confirm the trough’s presence or otherwise in this region.” So it seems there may well be a connection below sea level into the interior bottom of the ice sheet. Looking at their figure 3a this may also be the case from Petermann Glacier into the interior.
From Bamber et al 2013 (linked above), pp.506-507: “In the Jakobshavn catchment, there is a dendritic channel system extending for about 325 km from the current grounding line into the interior almost as far as the ice divide. It seems likely that this is a palaeo-fluvial feature that predates ice cover in Greenland and may be important for subglacial water routing… The width of the trough 3–4 km and the region of fastest flow coincides fairly well with the location of the deepest ice. The trough is 1366m below sea level at its deepest point compared to a maximum depth over the entire region of 556m below sea level in the older dataset. The main trough of Jakobshavn Isbrae is not continuous in the new dataset, disappearing around 100 km and reappearing at about 140 km. This does not imply that the trough is discontinuous, but only that there are insufficient data to confirm the trough’s presence or otherwise in this region.” So maybe warming ocean water could in time eats it way into the interior bottom of the ice sheet?
Kevin, Bamber et al 2001 has been recently updated by Bamber et al 2013: http://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf It's not clear to me if they think the Jakobshavn glacier extends all the way inland below sea level or not, but it seems it might.
More fragmented ice than ever all over the Artic, partly because of the cyclone: http://lance-modis.eosdis.nasa.gov/imagery/subsets/?mosaic=Arctic.2013169.terra.4km Thru the mostly clear sky and albedo flip warming and melting will now speed up. It will be interesting to see how fast.
Toggle Commented Jun 19, 2013 on On persistent cyclones at Arctic Sea Ice
Neven, I think many of us have moments like that. Someone like Paul Gilding has had them. He now says: http://paulgilding.com/the-great-disruption "The coming decades will see loss, suffering, and conflict as our planetary overdraft is paid; however, they will also bring out the best humanity can offer: compassion, innovation, resilience, and adaptability... The crisis represents a rare chance to replace our addiction to growth with an ethic of sustainability, and it’s already happening. It’s also an unmatched business opportunity: Old industries will collapse while new companies will literally reshape our economy. In the aftermath of the Great Disruption, we will measure “growth” in a new way. It will mean not quantity of stuff but quality and happiness of life. Yes, there is life after shopping." What doesn't kill us, can hopefully make us stronger :)
The complete Nature-article on MWP 1A is here and explains the uncertainty margins: http://sciences.blogs.liberation.fr/files/deschamps12nature-1.pdf An earlier one gave a range of 290-500 years for a pulse of 14-24 meters: http://oceanography.dal.ca/publications/files/Kienast_et_al._2003_Geol.pdf It seems the uncertainty is gradually narrowing down, even if there's still quite some debate on the sources/causes.
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Andrew, Nice overview, thanks. On Meltwater Pulse 1A there seems to exist some debate as to the probable sources and speed, with most estimates ranging from 3-5 m/century, but maybe even up to 10 m/century, if this Wikipedia entry is correct: http://en.wikipedia.org/wiki/Meltwater_pulse_1A Maybe that's where your 10 m/century came from? Also see for example: http://www.nature.com/nature/journal/v483/n7391/full/483549a.html The dating here seems to be extremely exact (duration of the pulse of 340 years). Don't know how reliable that is.
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Kevin, Goelzer et al would only be relatively comforting compared to for example Meehl et al. What I appreciate about Meehl's figure 3 is that they show explicitly a risk of much higher sea level than the models. But how well-founded is the estimation of that risk? Goelzer et al do acknowledge uncertainty, but don't give an estimation of the potential magnitude of that uncertainty, perhaps because they consider that impossible. Still, indeed, that may give the larger public a false sense of relative comfort as far as the potential risk of SLR is concerned. Lennart
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Rob, I think models are the best we have, if they have a minimum match with reality. We still have to judge that quality by some form of expert judgment or common sense, which still seems something better than wild speculation. Science also implies recognizing the limits of our knowledge, so the risk of putting too much trust in not yet fully enough developed models needs to be compensated by let's call it expert judgement. To me that's what Wadhams and Maslowski seem to provide, apparently to the annoyance of some of their colleagues?
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Andrew, Seems fair in general. However, that 10 m/century is new to me. You have sources? As far as I know, about 4-5 m/century during Meltwater Pulse 1A seems to have been the maximum speed in the past. But I'm just a layman, so may have missed something. Lennart
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
On modelling ice volume (and sea level) further into the future see this new article by Goelzer et al: http://iopscience.iop.org/1748-9326/7/4/045401/article As compared to this recent one by Meehl et al: http://www.nature.com/nclimate/journal/v2/n8/fig_tab/nclimate1529_F3.html Goelzer et al project until the year 3000; Meehl et al until 2300. The first expect less than 2 meters of SLR at most by 2300 and about 1 meter/century by the end of the millennium. The second seem to think almost 3 meters is likely under BAU by 2300, but don't exclude a risk of up to 12 meters and about 5-6 meters/century by then. How seriously should we take this risk? And how serious should we take Goelzer et al?
Toggle Commented Oct 4, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Even an average linear decrease of 400 km3/yr from now on would bring us below 1000 km3 in 6 years and to practically zero by 2020. Over the past 25 years the linear decrease seems to have been about 500 km3/yr on average. Over the past 10 years it seems to have been about 800 km3/yr. If that speed continues it would be about 4 years until the Arctic is ice free for the first time, and 3 yrs for the first time below 1000 km3. It seems Wadhams and Maslowski have a good chance of being right on the spot with their 2015/2016 projections.
Toggle Commented Oct 3, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
Geoff, Wadhams and Maslowski are supported I think by scientists like Jim Hansen in arguing that the/most sea ice models (amongst others) are not good enough yet to be trusted too much, to put it mildly. But Hansen also argues that many scientists suffer from a certain reticence and fear of being outcast as too 'alarmist'. Erring on the cautious side could in this case however be more risky than erring on the supposedly 'alarmist' side. So I think you have a strong case towards the politicians and the more people (and scientists) tell them so the better.
Toggle Commented Oct 3, 2012 on PIOMAS October 2012 (minimum) at Arctic Sea Ice
skywatcher, I agree with you that we should start from current science, so let's pick up again at the discussion between Pfeffer and Hansen. Pfeffer et al assume it's very unlikely, but maybe not impossible, that all GIS glaciers can speed up quickly to on average the speed of Jakobshavn Glacier in 2004-2005 (12.6 km/yr): http://courses.washington.edu/ess203/RESOURCES/READING/pfeffer_sealevel_science_2008_with_suppl_info.pdf They assume the same for the most important marine glaciers on AIS. For surface melting they assume continued acceleration at present day rates of change. Total SLR by 2100 could then be about 2 meters. Hansen & Sato think this may be too cautious an estimate (pp.22-23): http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf "The kinematic constraint may have relevance to the Greenland ice sheet, although the assumptions of Pfeffer at al. (2008) are questionable even for Greenland. They assume that ice streams this century will disgorge ice no faster than the fastest rate observed in recent decades. That assumption is dubious, given the huge climate change that will occur under BAU scenarios, which have a positive (warming) climate forcing that is increasing at a rate dwarfing any known natural forcing. BAU scenarios lead to CO2 levels higher than any since 32 My ago, when Antarctica glaciated. By mid-century most of Greenland would be experiencing summer melting in a longer melt season. Also some Greenland ice stream outlets are in valleys with bedrock below sea level. As the terminus of an ice stream retreats inland, glacier sidewalls can collapse, creating a wider pathway for disgorging ice. The main flaw with the kinematic constraint concept is the geology of Antarctica, where large portions of the ice sheet are buttressed by ice shelves that are unlikely to survive BAU climate scenarios. West Antarctica's Pine Island Glacier (PIG) illustrates nonlinear processes already coming into play. The floating ice shelf at PIG's terminus has been thinning in the past two decades as the ocean around Antarctica warms (Shepherd et al., 2004; Jenkins et al., 2010). Thus the grounding line of the glacier has moved inland by 30 km into deeper water, allowing potentially unstable ice sheet retreat. PIG's rate of mass loss has accelerated almost continuously for the past decade (Wingham et al., 2009) and may account for about half of the mass loss of the West Antarctic ice sheet, which is of the order of 100 km3 per year (Sasgen et al., 2010). PIG and neighboring glaciers in the Amundsen Sea sector of West Antarctica, which are also accelerating, contain enough ice to contribute 1-2 m to sea level. Most of the West Antarctic ice sheet, with at least 5 m of sea level, and about a third of the East Antarctic ice sheet, with another 15-20 m of sea level, are grounded below sea level. This more vulnerable ice may have been the source of the 25 ± 10 m sea level rise of the Pliocene (Dowsett et al., 1990, 1994). If human-made global warming reaches Pliocene levels this century, as expected under BAU scenarios, these greater volumes of ice will surely begin to contribute to sea level change. Indeed, satellite gravity and radar interferometry data reveal that the Totten Glacier of East Antarctica, which fronts a large ice mass grounded below sea level, is already beginning to lose mass (Rignot et al., 2008)." To me the key part seems to be that Hansen & Sato say the current "climate forcing is increasing at a rate dwarfing any known natural forcing", and this will continue under BAU. During interglacials the fastest SLR seems to have been about 2.5 meters/century, according to Rohling et al (2008): http://www.nature.com/ngeo/journal/v1/n1/pdf/ngeo.2007.28.pdf So if Hansen & Sato are right that the climate forcing this century is, or will be, much stronger than during previous interglacials, then it would seem to be reasonable that SLR could be much faster than 2.5 meters as well, if not already this century, then at least in the next ones. So what do we know about the climate forcings, now and during previous interglacials? The initial forcing now is mainly CO2. Back then it seems to have been stronger orbital summer insolation on the Northern Hemisphere. Both apparently cause strong albedo feedbacks. Hansen & Sato seem to argue the current CO2 forcing is an order of magnitude higher than the orbital forcing during the Eemian. If that's correct, wouldn't they have a strong argument for expecting more SLR than Pfeffer et al think likely? So does anyone know if the current forcing really is so much stronger than the one during the Eemian?
Jim, Agreed that an average doesn't show variations on shorter time scales. But to follow your extreme suggestion, what process could cause 2.5 meters of SLR in one year, implying a stable sea level the other 99 years?
Chuck, Interesting, hadn't seen that mentioned before. Another positive feedback by lowering albedo? Or otherwise? Lennart