Sam I have some questions. You suggest that the northern hemisphere would go to an equitable climate with a single Hadley cell circulation when the Arctic ice and Greenland ice disappears. Is it known how rapidly that would develop? Would the northern tropics then cool to the new average and if so how much? Is Greenland ice relevant since the average elevation of the ice sheet is over a mile?

Some German terms would add some color to the discussion. I especially like Schmelzsaison and Pfannkuchen-Eis.

Werther Stunning! Am I correct that you are saying that we are now (since 2007) in the middle of the hysteresis described by Langford in Allen McD's link? If so, this is a monumental tipping event that makes SIE a trivial concern. I have so many newbie questions: how long do you think it will take before the tipping completes? What is THC? Why is ridging on the 500Mb level where the action is now? What exactly is ridging on the 500Mb level? A new thread on this topic would greatly be appreciated.

I thought Nova Zemlya was the combination of the two adjoining islands Severny and Yuzhny.

3.1 M Km^2 = Wipneus's 3.2 projection of exponential trends shaded down to account for increased Fram transport as the polar high tends towards Greenland as Siberian side ice disappears.

The Fram is 500km wide. How could ice even tens of meters in thickness possibly jam in so wide an opening? Surely ice is not that rigid and uncompressible. Wipneus in an earlier post calculated that the volume of ice out the Fram appeared relatively constant with the speed increasing as the thickness was decreasing. The driver was apparently the prevailing wind and, unless that changed, the volume would likely not change. Of course that constant volume represents an ever-increasing percentage of the remaining MYI as it depletes.

SATire Evaporation killing the halocline is a positive feedback I have not seen discussed before. What produces the basin haloclines in the first place? Is it brine jets from sea ice formation taking salt to lower levels? I've read that these jets, if too vigorous, could actually cause mixing and disrupt the halocline rather than enhance it. Does sea ice formation in the vast areas previously covered by MYI strengthen the halocline or weaken it? Is it generally agreed that total destruction of the halocline would produce a year-round ice free Artic? Sorry to be such a pest with these elementary questions.

Kevin McKinney In the article you cite, the blooms are diatoms that have silicon-based shells and their fall does not involve CaCO3. Of course, the falls involve more than just the shells and carbon would deposit from the contents of the shell regardless of the shell's composition. The loss of nutrients, such as silicon in the case of diatoms, would constrain this process and I doubt it would therefore have much effect on CO2 levels in the atmosphere.

Kevin McKinney Algae blooms and subsequent falls do not necessarily remove CO2. These blooms are often coccolithophores with calcium carbonate (CaCO3) shells. Their fall removes one CO2 but also one calcium. That calcium otherwise could hold two CO2s as the bicarbonate (Ca(HCO3)2). The fall actually reduces the CO2 holding capacity of the ocean.

Guess not...

Does this kill the italics?

Steve The western boundary ocean currents are driven by winds that are steered by the Coriolis effect but powered by the atmospheric polar temperature gradient through Hadley, Ferrel, and Polar cells. If the gradient declines, do not the winds decline accordingly? It is the role of those winds in bringing water-laden air from the ocean to the land that concerns me, not so much their role in driving ocean currents.

Chris Arctic crocodiles? I assume you meant Eocene, not Eemian. The heat flux from lower latitudes hypothesis to explain the equable climate problem posits ocean currents, not atmospheric currents to carry heat to the poles. It was seasonal diminishing of the atmospheric heat difference that was worrying me. The resulting blocking events would be primarily a summer phenomenon; other seasons would perhaps be even more lively than they are now.

Kris The heat to melt a meter of ice will instead warm a meter of water by 80ºC (or 10 meters by 8ºC). I would think the arctic waters would warm rather quickly even within one season. I don't know about the Gulf Stream; I was referring to the atmospheric heat engine.

Steve Bloom I did not mean anything pleasant by the term 'tropical'. If the Arctic temperatures approach even temperate levels in the Arctic day (spring and summer), I think the first catastrophic consequence will be a shut-down of the heat engine that drives NH weather. With no summer winds, ocean air will stay over the ocean and land air over land. This stagnation will cause massive summer drought in mid continents of the NH. If Wipneus' projection of June ice holds, this could happen within 8 years.

In a Scientific American guest blog, Ramez Naam stated: In fact, in June, July, and the latter half of May, the Arctic receives more total solar energy per day than regions at the equator do at any time of year. The sun's rays are never as powerful in the Arctic as they are at the equator, but the 24/7 availability of sun more than makes up for that. Is this true? Could the Arctic see tropical temperatures when the sea ice is gone?

Terry Why would NH temps be so much higher? Heat radiates to space everywhere and every season and 18.6 Km3 of melting potential spread over half the globe might not be all that significant temperature-wise. What I fear more than higher temps is perennial summer drought over all the continents as the driver of the westerlies, the temp delta between the Arctic and the tropics, is diminished.

Could not Wipneus' map be enhanced to account for standard ice drift to correct the anomaly of "the blue's and beyond...near the 'drains'"? That would surely chop off the Gomperz tail.

Nevertheless there seems to be little area of effectively cold ice to hold a stationary high over Greenland. Also does it suggest that Arctic Summer temps will rise over 57°F when the Summer sea ice is gone before the GIS has any moderating affect?

P-maker ...If we see another year with an extended period of anticyclonic circulation centered over the Greenland ice sheet (being the only solid chunk of cold ice left in the NH)... Is the GIS really cold? At an average altitude of 2,135 meters, a standard lapse rate of 6.4°C/km makes the GIS at 0°C no colder than sea level at 14°C (57°F).

I guess it makes sense that the volume of ice out the Fram would be constant since the energy to move the ice (the wind) is constant. The implication then is that there is no negative feedback foreseeable in this process (until it clips at zero, of course).

Wipneus Would it be correct to conclude from your Fram flow graph that the annual average volume is essentially unchanged since 1977 despite the thickness of Arctic ice at the start of the melt season having dropped by about a third since 2005 and I presume much more since 1977? If the ice is getting thinner why is the volume not dropping?

I meant 40 meters, not 10.

Rob Thank you for your reassurances. I appreciate how simplistic it is to imagine all the excess heat attacking the GIS as the coldest remaining target in the neighborhood. Firstly it may not be in the neighborhood at all. If a summer high sits on Greenland, would that isolate the GIS from the circling Arctic winds? Also if those now warmer, wetter winds could climb up 2km to the GIS would they not cool adiabatically below freezing and drop their moisture as snow and tend to lower sea levels? These are not rhetorical questions; I have no idea and would appreciate expert responses. I also understand that glaciers and ice sheets are not the same thing and that disappearance of all the glaciers of Greenland would have little affect on sea levels. Also the GIS would have to thin 10 meters per year to lose 2% of its mass per year and that might be improbable fluid dynamically. If the Arctic ocean water does warm to 7.6degC as you suggest, would that not destroy the clines and allow the warm waters below to enter the mixed layer. If so, would not the surface waters stay warmer than 0degC for the winter until all that legacy heat is vented? Would that dump more snow on the surrounding land areas possibly including the GIS?

So here is my worst-case nightmare take on the near future based on the responses here to my questions: By 2021 summer sea ice has virtually disappeared. Albedo decrease results in 20,000 Gtons per year of additional melt on the only ice left, principally the GIS. The heat that used to melt the sea ice is also available to melt another 17,000 Gtons per year. Any of this heat diverted to warming the Arctic generally will result in more positive feedbacks from permafrost thawing and destruction of the ocean halocline/thermocline resulting in even more GIS melting. With the GIS approaching a 2% loss of its mass per year, 7 meters of sea level rise will occur in 50 years or 1 meter in 7 years. By 2030 massive coastal flooding will be commonplace and every location unable to withstand a 7 meter rise will be a financial write-off. My house at 10 meters will be ok but my friend's house at 3 meters will not. Maybe now is the time to sell...