Volume April 1979 by PIOMAS ~ 33 K Km^3
Area April 1979 14 M Km^2
So Average thickness 2.36m
Volume April 2014 by PIOMAS ~ 23 K Km^3
Area April 2014 ~ 13M Km^2
So Average thickness 1.77m
How FYI could have been 3m thick when MYI is thicker than FYI escapes me.
http://www.arcticnet.ulaval.ca/pdf/ASMtalks/StudentDay/Galley.pdf
on page 7 says
first-year sea ice can grow to typical
depths of ~1.80m in the Arctic
Typical 1.80, yes. Did i say "typical"? No. I said "maximum" FYI thickness. "Maximum" and "typical" - are two different things. "Average" is also not "maximum". Perhaps you thought i meant "maximum average thickness" in terms of maximum annual value of the avreage FYI thickness? I didn't. I meant absolute maximum thickness of FYI "in some spot" - i.e. "how thick FYI can get in a single place".
As for where i get it from - why, looking at graphs here and there, i love those color-coded maps. It's much faster than to dig into mountains of discrete data, too. For example, one can see clear map for where FYI (and MYI) was located during MArch 2013 here: figure 5 on
https://nsidc.org/arcticseaicenews/tag/first-year-ice/ page. According to it, there was no MYI to talk about near north shores of Alaska and Chukotka. Very conviniently, figure 6 of the same page presents ice thickness map (also color-coded), for March 2012 (right image of the figure 6). It is made based on Cryosat-2 data - which means it's not some smarty-pants model, but actual "what was there in reality" measurement. And on it, i can definitely see some green color (means, ~3 meters thick ice) near north shores of Alaska and Chukotka - considering the scale of those images, we are talking here about thousands of square kilometers of such ice. There are even few small patches of almost-yellow - which means it's hundreds square kilometers of ~3.5-meter-thick FYI there.
Why those locations get maximum FYI thickness - i don't know for sure, probably a combination of relatively cold near-surfgace water currents and extra-chill of the athmosphere from much-more-rapidly cooling large landmass nearby (Alaska and Chukotka, i mean). Still, it's very easy to see that maximum thickness of FYI is indeed ~3 meters, give or take; while typical FYI thickness is, indeed, some 1.8 meters.
There's also the mean atmospheric lifetime of methane, which is much lower than that of CO2.
Even if methane has ~34 time the GHG potential, the short lifetime (IMO) makes it a less significant pollutant. ...
I'd add to previous reply to this that i've recently estimated methane's greenhouse-effect CO2 equivalent ratio (by mass) for a duration which is many times shorter than methane's half-life (which is 1 year or any shorter duration), using two different methods (quite rude, but simple ones) to do so. 1st method gave me x124. Second gave me x131. This is close to results many other people get - including most competent scientists, - for short-term methane GHG potency.
Also, methane can't be "less significant pollutant" than CO2 - EVER, because in the athmosphere, methane (CH4) gradually turns into carbon dioxide (CO2) and water vapour (H2O). For every CH4 molecula, one CO2 molecula is formed. Thus, methane _becomes_ CO2, with 1 to 1 ratio - and CO2 can't be "less significant pollutant" than CO2, can it? On top of CO2, said reaction also forms 2 moleculas of water, and water vapour is a strong GHG gas as well.
...
The only salvation is that due to the short life time, CH4 forcing will drop shortly after emissions decrease. I hope that this transient rise in AGW will increase the change in energy generation.
Relevant to the thread topic:
A transient spike in forcing and AGW, as long as the GIS and WAIS do not collapse; is much easier overcome than the centuries of forcing related to the release of CO2.
Unfortunately, methane deposits (in the form of gas and in the form of methane clathrates), plus organic until-now-permafrost soils and seabed layers which emit large amounts of methane once thawed (due to bacterial unaerobic decomposition of organic compounds), - all this in total, in Arctic alone (not talking sub-polar, not talking deep-ocean deposits even closer to equator, and not talking any southern hemisphere) - is estimated to be more than 10 thousands gigatons. ESAS alone contains some ~1400 gigatons of methane, and it's burping much already. Some places near Norway are also emitting methane massively already. AMEG says it was more than 100 millons tons of methane emitted in 2013 in Arctic. I.e., 0.1+ gigaton. Annual emissions back in 1980 were, iirc, some 7 millions tons or something like that.
In other words, there are LOTS of methane presently frozen or trapped under frozen soil and sea floor - more than 10.000.000.000.000 tons of it. What methane Arctic emits so far, - is only a tiny fraction of what will be emitted annually once Arctic warms up for real (i.e., loses most of its June'July ice and snow, this most of its albedo during those high-insolation months).
You said: "after emissions decrease". Well. Bad news are, methane emissions in Arctic won't start to decrease for at very least ~120 years from now. May be times longer, even. By 2025, i think Arctic will release some ~1.5 gigatons of methane annually, plus-minus 70% of that. By 2050, may be some 2.5...5 gigatons. By 2100, perhaps some 4...20 gigatons. Yet, if this will be the pace, - then during 21st century, Arctic will release only some 500 gigatons of methane, total (something of this order of magnitude, i mean). Yet, 500 gigatons - is less than 5% of the total amount (which is, again, more than 10,000 gigatons - probably much more). So even if most of potentially releasable (because of disappearance of permafrosts) methane will remain in the ground for CENTURIES, - the lesser part is still enough to maintain 1+ gigaton annual Arctic methane emissions for several hundreds years.
It a major deal for whole planet; for Arctic itself - it's enourmous, since being point of origin, it'll naturally have higher concentration of methane. It already does, substantially.
Therefore, "after emissions decrease" = "some 500+ years in the future". Frankly, i don't think it's any kind of "salvation" to the current AGW situation... And, both GIS and WAIS will probably collapse in 500 years (i know old papers say it's "thousands years" for WAIS - but old papers have many massive underestimates, besides, who knew, back in 1990s and 1970s, that last two decades - to nowadays, - will be most feverish GHG emissions ever done). Some chances are WAIS wouldn't fully collapse in 500 years, - but GIS will definitely collapse, and much faster than in 500 years, too. No doubt about it.
P.S. By the way, there are some 50,000+ people permanently living in Greenland. It's a country. They have a capital city (more like, a town). In it, they had nice little bridge over a river - two dozens meters or so. They "had" it, because at some point few years ago, the bridge was washed away. Literally. Too much meltwater going outta GIS. They probably rebuilt the bridge, for now, since it connects two "halves" of the town - much needed bridge, important one. But i think, in about 15 years, this whole capital town of Greenland will be washed away right into the ocean - sooner or later, they'll get large enough melt pulse (it's when large mass of water trapped inside ice sheet - finds an exit "down and out"). By the way, i believe that this is the type of event which, during last ice age's end (deglaciation), caused lots of death - and gave humans survivavors strong memories about "great flood", which eventually ended up written down in several religions (among others, in the Bible, too).
