Some folks didn't care for my guesstimate of how rapidly Greenland could melt.
I suggested 100-200 years after the loss of the last Arctic ice.
Consider: Greenland's ice sheet is estimated to contain about 2,850,000 km3 of ice. That is melting today at a rate of about 195-239 km3 per year. With an area of 1,700,000 km2, the ice is on average 1.67 km thick. That's a lot of ice.
{apologies: I had an atrocious blunder in my original post, now corrected. Thank you to SteveMDFP for pointing that out!}At the current rate, Greenland would take 12,000-14,500 years to melt.
During the Eemian interglacial ~130,000 years ago the ice sheet lost 150-650 meters of thickness. That resulted from the local warming of 8 C. Today, we are at a global warming of ~1 C with at least 1 C more already baked in, and a total potential global warming of 3-4 C as the best case and 13 C as the worst case. Recent US Government estimates are now 4-5 C.
These all result in local warming to Greenland vastly higher than the relatively brief Eemian warming.
"In a 2013 study published in Nature, 133 researchers analyzed a Greenland ice core from the Eemian interglacial. They concluded that GIS (Greenland Ice Sheet) had been 8 degrees C warmer than today. Resulting in a thickness decrease of the northwest Greenland ice sheet by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than at present.[13]"
https://en.m.wikipedia.org/wiki/Greenland_ice_sheet "Eemian interglacial reconstructed from a Greenland folded ice core". Nature. 493: 489–494. January 24, 2013. Bibcode:2013Natur.493..489N. doi:10.1038/nature11789. PMID 23344358.
Over the last many decades, the Arctic ice sheet has annually melted ~15,200 (circa 1980) -17,900 (now) km3/year averaged over many years. Individual years have lost more or less than this. The annual melt volume rate is increasing. This change may be due to the loss of ice on the continents, or the warming of the continents. It seems likely that the heat transfer will reach sufficient levels to melt 20,000 km3/year.
Once the Arctic ice is gone, that heat shifts from melting the Arctic ice to warming the Arctic Ocean, warming and melting the permafrost, and melting Greenland.
If only half of that total energy goes to melting Greenland's ice, the ice will be gone in 285 years. If all of it goes into melting Greenland, the ice will be gone in ~142 years.
However, even these simple estimates make some horribly wrong presumptions. They presume that despite the loss of the cold pole that the heat engine driving atmospheric circulation will continue to operate as it currently does. That is of course absurd. It will collapse.
We do not understand yet what happens when that collapse occurs. We particularly do not understand what happens when the remaining cold (Greenland) is asymmetric to the rotational pole.
It seems highly likely that the standard three band atmospheric circulation will collapse. The beginning of that will be, as we have already seen, a slowing and deepening of the Rossby waves. This will drag cold south and heat north in waves. Eventually, as the driving force falls (the cold pole melts), this will destabilize further. In the extreme, once all of the ice is gone, it collapses entirely.
Heat then builds to the south expanding the atmosphere and elevating the tropopause. The dynamics then shift. Air circulation extends further north as the jet streams are compressed toward the pole, though with huge variation as already seen. Eventually, these collapse into chaos and a state change inevitably occurs in the system.
A two band circulation is unstable. That requires rising air over the North Pole. And so, most likely, we step change to a one band system with a persistent cyclonic storm over the pole. My guess is that the higher Arctic heat leads to persistent cloud cover through most, or all, of the year further insulating and warming the pole. This further accelerates the rate of transition.
Temperatures then rise dramatically over the whole Arctic. For a time Greenland resists. Now pounding with rain and heat, the melt rate over Greenland rises dramatically, eventually exceeding ~12 meters of ice loss per year at its peak. And in 140-<285 years after the Arctic goes ice free, the Greenland ice is gone. So, by about 2170-2335, with the highest likelihood on the low end of that.
And if we continue with business as usual, which seems to be a foregone conclusion based on the recent US, Brazilian, European, and other elections (and the public sentiment that drive those), then the driving heat rise is likely to reach 8-13 C ultimately. That hugely increases the melt rates and the dramatic shift in the Earth's atmospheric, oceanic, and ecosystems.
Under those conditions, conceptually at least we could see Greenland ice free and a global sea level rise of over 7 meters before 2150. My suspicion is that the dynamics of it will result in greater heating of the Arctic Ocean and slower melting of Greenland with the net result being an ice free Greenland closer to the year 2200-2250. But that is guess-work. A lot of the heat will also no doubt go to melting the Himalaya, creating yet another set of catastrophes.
But this is by no means the worst case, or even the most likely case, scenario. If, as expected, the Arctic Ocean releases 50 GT of carbon as methane from clathrates, and the tundra releases 1,650 GT of carbon as methane and CO2, these estimates all shift to higher global mean temperatures vastly higher Arctic temperatures, rising ocean temperatures and far faster melt rates.
These are each and all by any measure geologically instantaneous changes in Earth's conditions.
Needless to say, most creatures cannot survive such a rapid transition. Concomitant with this we must expect large swaths of land area to exceed the ultimate wet bulb conditions that disallow human survival in those areas. This has already begun in a swath from Iran through Pakistan and India. Combined with widespread drought and deluge as the warming soaks in, and the climate bands breakdown, we will see acceleration in the mass migration of people, starvation, pestilence, and war to name but a few of the horrid impacts.
My only consolation is that I am old enough that I likely will not live to see a fully ice free Arctic Ocean, and hence not see the beginning of the calamities to follow. But that is cold comfort, as the global changes with population migration and other disasters has already begun. These will accelerate in scope and impact until the Earth stabilizes into a new 'normal' for the northern hemisphere a few centuries from now. That new 'normal' seems likely to look a lot like the Eocene.
The focus then shifts to the melting Antarctic ice and the ultimate question of whether mankind was so foolish as to push the Earth's systems so hard that over a few millennia the Antarctic goes ice free. I doubt that. But 30 years ago, I would not have believed mankind would be as foolish as we already have been.
Sam
