Thank you for the chart grixm. It's worrying to see this year leading in that metric. Though it does appear that recent years bunch together come summer.
I join the tanks to grixm for the graph; much appreciated, and definitely timely per concerns further in this post.
I apologize for somewhat lengthy remainder of this post, but i think this is way too important; like, 2020's "must know" thing for the melting season (and for lots of other things too).
This is in response to the reference of "recent years" by Davidsd. This year is much different from recent years, and much more so than lots of people here could probably imagine.
1. China stopped most of its transport and industries for a fair while, and lots of it - half, give or take - are not back even now. This is now being followed globally: fuel burning by mankind is decreasing by the day, as reflected by oil prices;
2. This means less aerosols in the athmosphere, to say the least. Plenty cities in China were observing the stars clearly for the 1st time in decades, so strong was reduction in air pollution there. The normal effect of global dimming at the surface is quite massive on average over continents, too - over 10%, at places well over 15%, as was discovered by both pan-evaporation measurements, other methods and eventually multi-national 4-year INDOEX measurement effort (some details freely available here:
http://www.bbc.co.uk/sn/tvradio/programmes/horizon/dimming_trans.shtml ). In the same piece one can also find summary of findings about direct effect of absense of jet contrails, which was found to be much bigger and more rapid in practice than anticipated.
3. As a result, right now (as well as progressively stronger during last couple months as the situation develops) - significantly less sunlight gets "caught" by aerosols before it reaches surface, which means less of cyclones (direct consequence of comparatively less heat content in the air), so more shiny days on average scale, and faster melt ponding / top melt in the local scale. So far, most of GHG effect - in the Arctic as well as around the globe - was negated by aerosols in this way, and lots of it still is, but the changes are big enough to already be a game-changer as far as ASI melting season is concerned as a whole.
To understand the scale and importance of those effects, it is enough to remind oneself that industrial activities since the industrial revolution have injected nearly 5000 Tg of SO2 into the athmosphere, with recent years being ~7...10 Tg/year - and that famous Pinatubo eruption, responsible for significant cooling of whole Earth's climate, released only ~1 Tg of SO2. Thus, even "modest" 10% cut of aerosol emissions by mankind can produce changes comparable in magnitude to Pinatubo eruption - except not to cooling, but to warming the climate. Further details about how aerosols work and plenty references for great number of good papers - can be seen here:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015RG000511 .
That same piece also describes timescales relevant for aerosols' lifetime in the athmosphere, which depending on type, size and source of a particle will vary from some hours to some months - with everything tropospheric leaning towards much shorter lifetimes (days to few weeks at best, usually) as precipitation washes 'em down to surface.
Same piece also mentions the following processes, to give a short quote here (by bold):
"In the stratosphere, strong zonal winds lead to fast homogenization of aerosols and tracers in the zonal direction, while vertical and meridional transport is controlled by the BDC [Holton et al., 1995; Butchart, 2014]. The BDC results from the breaking of upward propagating waves in the stratosphere that lead to a diabatic residual circulation [Holton, 2004].
The residual circulation is characterized by ascent over the tropics, poleward motion in the extratropics, and subsidence over the high latitudes, in particular over the winter polar vortex, ...".
So, with rather big uncertainties about how yet worse microbiological situation will become in the following weeks and months, but with rather big certainty that lots of intercontinental jet flights over the Arctic are not happening and won't be happening any time soon, i can easily conclude that "recent years" are not a predictor of anything, now.