01-26-2017, 09:36 PM
(01-26-2017, 09:14 PM)X_4AD_84 Wrote:(01-26-2017, 08:04 PM)Odin Wrote:(01-26-2017, 03:51 PM)X_4AD_84 Wrote:(01-26-2017, 08:05 AM)Odin Wrote:(01-25-2017, 05:37 PM)X_4AD_84 Wrote: The actual worst case scenario would probably be matching the previous interglacial in terms of sea level stand.
So far that does not appear to be likely. The rate of sea level rise is not currently enough to hit that level. Broad brush, the rise curve is still a decaying exponential which makes sense given how much of the continental ice has already retreated since the most recent glacial advance. What is really surprising is that the apparent amount of heat and work now in the oceans is estimated to be roughly the same as it was this far into the last interglacial. That sort of result seems to point to some mode that might be different than it was during the past interglacial, preserving more of the ice than was the case at a similar point back then. It may actually be an anthropogenic effect, perhaps the Asian Brown Cloud or some such. Now countering that (above and beyond GHGs) is the impact of soot. It may be that soot has more of an impact on sea ice than it does on serious glacial masses. Lots to learn still on this topic.
As far as I know the consensus among climatologists is that if CO2 levels exceed 550ppm there is nothing stopping the climate from flipping over into the hot-house mode due to all the positive feedback loops. It will take several thousand years for all the ice to melt, but melt it all will.
During the last interglacial, most of the continental ice was gone from the Northern Hemisphere, there was much thawing of perma frost, and the Arctic was free of sea ice every summer. There can be some debate about how high CO2 not to mention other GHGs got at the time. Nonetheless, there was no hot house. I don't even know what that term means. I suppose to some adherents that means going into something like the Carboniferous. That would be pretty tough given how much the mixture of major gases has changed, and the fact that the Equatorial Current can't circle the globe now due to the wall of The Americas and the near wall of SE Asia, India and Africa. The next opportunity for that sort of regime is hundreds of millions of years in the future.
I meant ALL the ice, even in Antarctica. The Earth shifts back and forth between two stable states, the hot-house world when the poles are ice-free and the deep oceans are warm and low in oxygen, and the ice-house world, where there is ice at the poles and the deep oceans are cold and oxygenated. Our current ice-house phase began at the end of the Eocene when the Antarctic ice sheet began to form.
The Carboniferous and early Permian was actually an ice-house world like our own, with a massive ice sheet at the south pole, and glacial-interglacial cycles exposing and then inundating the tropical lowland forests that became the great coal beds of Appalachia and Western Europe, the CO2 levels dropped to 300ppm at the end of the Carboniferous.
Even some of the more radical models would not give a temp rise sufficient to compromise Antarctica's main continental ice masses. It's at way too high of a latitude and even in "summer" it rarely rises above freezing in the interior.
The reason our current ice phase began when it did was the closure of the Isthmus of Panama. That gave an ocean current configuration that made Earth prone to glaciation.
One big fallacy is the notion that as goes the Arctic sea ice so goes continental glaciers, most especially Antarctic ones. Obviously, sea ice behavior will be influenced by multiple factors beyond the ones affecting mass balance of continental glaciers at extreme high / polar latitudes. A modest rise capable of causing summer ice free conditions at the North Pole is not going to "un Eocene" Antarctica.
My concern is the earlier expansion of antarctic sea ice, for which one possible explanation is warming and more rapid flow of antarctic land ice to the ocean. I wasn't too concerned when we had reached peak liquid oil and seemed to be moving toward renewables and conservation, but add the return of shale oil carbon to the atmosphere, and warming could go much farther. I can imagine returning to mesozoic temperatures before shifting away from a fossil fuel economy.
That said, we're also overdue for an ice age, and that would be at least as bad for us. If we're going to start taking control of the climate, we need to be careful of both extremes.