The subject of year-round ice-free Arctic surfaced in the ongoing Melt Season thread, and it is best we continue the discussion in this topic.
... Even with much higher temperatures, there will probably always be freeze in winter, that's why there will probably never exist zero ice all over the year...
What you are discussing is the transition of the Arctic Ocean from being perennially ice covered, through seasonally ice covered, and ending up in a perennially ice free condition.
One such study appeared last year in the Journal of the American Meteorological Society. Their findings, in a nutshell, were that the vast bulk of winter sea ice could be a thing of the past by as soon as ~2130.
I'll put more flesh on this later, but I'm off to sink a few pints.
Bill, excellent spotting about that paper! But i am sure their result is a vast underestimation. I am not familiar with the paper, but i could bet authors did not take the biosphere influence into much consideration when making their calculations. If so, then that is perhaps the biggest flaw of their work. Because, obviously, in real world, we _do_ have the biosphere. So far. Thank God for that, if i might add.
As you can see in
this lecture by no other than James Lovelock himself - the "father" of Gaia theory, inventor of the detector which allowed to detect ozone holes, etc, - he predicts a distinct state change into "Hot House Earth" (a.k.a. "Jurassic Park Earth") some time during 2050s. I recommend you hear his own explanations about how and why he produces such a graph; they are very good, you can hear them at the beginning of the video i provided the link for.
Further, what James does not say is full version of why there are higher and higher volatility in his graph before 2050, and why there is smaller volatility after the state change (2060s and beyond). The reason for that is that biosphere attempts to regulate temperatures using its ability to do so, but with greater and greater positive forcing and (not changing in James' model - static) ability of the biosphere to regulate it, the regulation becomes less and less potent, thus producing wilder and wilder swings.
Obviously after the state change, positive forcing becomes much reduced (becase new quasi-equilibrium temperature is higher, so Stefan-Boltzman law does much bigger work radiating extra amounts of energy into space without biosphere having to deal with it). Thus less volatility after the state change.
Next, while i agree with James about everything he says in this (3rd) part of his lecture, i can't help but be sure that there is one thing James' model did not yet completely account for: the ongoing 6th great extinction of species. In particular importance, ongoing deforestation, rapidly increasing amount and scale of forest fires, and ongoing loss of phytoplankton in the oceans. All those trends are most likely to continue into observable future, thus further reducing biosphere's ability to regulate temperature of Earth surface at large.
In turn, that reduced ability means that the state change will happen sooner than predicted by James' model he presents in the lecture. So, we're talking something like "some time during 2040s, in best case as late as year 2050 or so".
And that's even before we start to take into account vast uncertainty presented by melting permafrosts and associated methane releases. Clathrate gun hypothesis, you know. Obviously nobody can quantify its effects any well - for now. But the thing is, nearly everyone calculates things as if Clathrate Gun would be minor and/or distant factor. What if it's not either minor nor distant? 2030s for state change of the kind James talks about?
You get the picture. 2130s? I wish. But nope. It'll be much, much sooner. Certainly this century, if you'd ask me.
Thoughts?
P.S. i vastly disagree with few things James says in other parts of that lecture, even though i respect him extremely much. I just can't agree; notably the one about his proposal to tinker with the biosphere feedbacks: i'm extremely cautious about any such proposal. To me, it's like practicing middle ages medicine methods which can lead to death of patients. Simply because methods used would not be sufficiently safe. We should not attempt to regulate the climate via any biospheric methods unless we understand very well and in every detail how Gaia works. Which we don't. And which we won't for a long time ahead - Gaia is much more complex than "just a human body", and it took our civilization many centuries to learn the latter only. Did you know "doctors" could literally kill your kid just few hundreds years ago trying to treat the kid's stuttering, for example? But it's true, and feel free to scroll on
this page to other similar examples of "medicine" methods widely practiced not so long ago, and in some cases even today; and that list was just a warm-up - if you appreciate black humor, them check
this one, too. So, it is so tempting to genetically engineer some climate-change-preventing-algae or something, but i think we must not: unlike human patients, whos death is tragic but is not yet the end of the world, if we "mis-cure" Gaia - there won't be another patient to experiment on. If through our misunderstandings and limitations we end up destroying most of the Gaia (to the level of only remains of microbiota remaining) - then Guy McPherson will end up being right, i think: then we'd extinct as a species, ourselves.