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If an average year used to be able to remove swathes of 2m FYI then what of an 'average year and 1.5m ice?
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I understand this one was meant mostly as rhetorical question.
However, it is not.
"Average" year nowadays is quite very different from an "average" year mere 2 decades ago. And my point here is, some changes are not for the worse - but for the better. In terms of melting potential. In other words, not all feedbacks are positive; some are negative, and may prevail.
In particular, - more clouds. We are seeing it this melting season quite very well: cyclon in this June was almost strongest-ever for the month of June, and if models have any sense in them (i think, they do, a little at least), - it could yet be much stronger, beating the record for lowest June Arctic air pressure by a ton. Didn't happen, but "was close", yes?
Earlier in late May / June we had that "could be persistent" pattern with 5 lows around 1 high in the middle of the Arctic, - and that's 5:1 in favor of low pressure regions, i.e. roughly 5:1 ratio for places with "lots of clouds" against places with "clear sky", yes?
Furthermore, we now see in forecasts - as recently mentioned, - more cyclonic weather coming in Arctic's way. Overall, those recent examples, as well as similar occurencies in recent melt seasons, - starting with the famous GAC of 2012 and through windy and cloudy Arctic times (lots of times) of 2013 and 2014 in particular, - all those are clear indication that in general, Arctic is becoming much, much more cloudy place.
I lived near the polar circle for the total of 11 years of my life back in 1980s and 1990s. And so, i know "classic" northern weather in general quite very well. One definite feature of it is relatively short but intense "wet" periods between much longer, stable, lasting "dry" periods, - both winter-times and summer-times. This old-standard Arctic feature is easily explained by three simple facts:
- relatively low amount of moisture in the athmosphere in general, because evaporation from permafrosts and not-much-melt-ponded ice fields (especially with snow cover) is very low;
- real big temperature gradients between masses of much warmed up relatively dry air (dry air is getting warmer faster than high-humidity air), and whatever high-humidity "imported" air masses happening to enter the Arctic. Those big gradients, in the past, were one big factor which intensified "wet" processes in Arctic athmosphere, leading to faster movement, compactness and intensity of thunderstorms and such;
- the Jetstream was much more effective in separating Arctic part of Earth's athmopshere from temperate regions, much limiting "import of moisture" into the Arctic.
But now all that have changed quite very much. And so, we get the big-time increase in cloudyness in Arctic. Summer-time, cloud cover prevents lots of direct insolation happening near-surface, potentially allowing 1.5 meter FYI to _survive_ an "average" year where previously, 2.0 meter FYI would just melt away under the Sun.
However, clouds are not only about that negative feedback of "cutting direct insolation off". They also do positive feedbacks, too. Especially autumn and winter-times, that is.
If to continue the example i made just above, - as much as they prevent sunlight from reaching the surface, they also prevent much of IR from escaping the surface, too: where lots of IR would travel directly into near-Earth space through the clear skies, most of it ends up being sent "back to the surface" if there is significant cloud cover over the area. That's one of primary reasons last winter was so little freezing for the Arctic, in particular, - which have led to this "1.5 meter thick instead of 2.0 meter thick" situation in the 1st place!
Furthermore, it's far from being only radiation-related feebacks (both positive and negative). Clouds also produce extra precipitation, and that's whole another story (even bigger one).
They clouds also tend to transport various kinds of pollution quite much better than dry air would, which is increasingly relevant with things like intensifying (lately) forest fires in high latitudes (Siberia, Canada), recently mentioned oil leakages (hundreds thousands tons into Arctic waters directly i mentioned before, - is but a joke in compare to many million tons of oil leaked, and sometimes burned, across Siberia and from Canadian "tar sands" and alike operations). There are real great papers and whole teams working on speicifics of cloud droplets and snowflakes forming around soot particles, for example. Etc.
Another possibly game-changing thing is that nowadays we have increasingly intensive air traffic over the Arctic. Both civilian jet liners and military craft fly all sorts of directions over the Arctic, leaving contrails behind. When US grounded their civil jet liners after 9/11 for just 3 days, daily temperature gradient over most of US soil increased by ~1°C (which is huge value, as usually that metric is very stable). Plus, we don't exactly know what kinds of "additives" and "components" modern jet fuels are having in them, exactly; one i've read about mentioned having alluminium-based compound in it, as "anti-corrosive" component for jet engines to enjoy, - but the thing burns into simple Al2O3 inside the engine and then gets ejected into Arctic lower stratosphere, and that's potentially Welsbach seeding with its known effects (depends on specifics of the compound, engine exhaust and more - may or may not be effective the way Hughes corporation patented it). How much that affects an "average, today" year? Your guess is as good as mine - i don't think there is any published dedicated research on this specific subject (might be wrong). If significant, that's another negative feedback, to further reinforce the general point of this post. Which is, to remind:
nowadays, despite most trends, "average year's" melt season might be melting _less_ ice thickness than "average year 20+ years ago" was able to.
Whether it is in fact so, and how much is the difference, - probably noone can say for sure, but as i tried to argument above, there are reasons to consider it true.