Huh? They say
"....the Arctic could become ice-free in summer for the first time within the 21st century. Projections with CMIP-5 (Coupled Model Intercomparison Project Phase 5) models show that this could be the case as early as 2030 to 2050 for higher emission scenarios such as RCP8.5 (Representative Concentration Pathway). Some GCMs (global circulation models) show an ice-free Arctic for the first time within this century also for the moderate emission scenarios at a warming of 1.7 °C above pre-industrial. Furthermore, observations reveal that the Arctic summer sea ice declines faster than expected in experiments from GCMs."
Which is accurate when the term "ice-free in summer" refers to < 1M km2 ASI Extent at September summer minimum.
Then they are vague about what ASI Extent or Area they plugged into their model. But in Figure 1a the caption says "Regional warming for the whole Earth
if Arctic summer sea ice (ASSI) in June, July and August, mountain glaciers (MG), Greenland Ice Sheet (GIS) and West Antarctic Ice Sheet (WAIS)
vanish at a global mean temperature of 1.5 °C above pre-industrial. (bolding added by me).
ALL ASI vanishing in June July and August (as in zero Extent-Area-Thickness-Volume) during peak solar input is an entirely different scenario than reaching ASI > 1M km2 Extent for a couple of days in September before refreeze resumes.
So which is it? <1M km2 ASI Extent or Area at September minimum, or ASI vanishing to give zero km2 ASI for June 1 - August 31? Based on the Fig. 1A caption, it seems to be the latter, which renders that first paragraph completely out of context with their simulation and egregiously misleading.
Before noticing the aforementioned oddity, my hackles got raised by Figure 4. It is one of the most easily misinterpreted, and therefore poorly designed, data graphics I have ever seen. The X axis on a chart implies that X values cause the Y axis values as a response. But that is not really what is happening in Fig. 4. A reader could all too easily look at that chart and think it says that at 2.5C above preindustrial global mean temperature (GMT) we should expect 4M km2 summer ASI Area.
At
https://forum.arctic-sea-ice.net/index.php/topic,2975.msg286961.html#msg286961 our friend gerontocrat made it back safely from his foray into the COVID-19 infested streets to buy booze to let us know that on September 18 ASI Area reached 2,631,888 KM2.
2020 is coming in hotter than expected, with a good chance of beating out 2016 as the warmest year in the modern record (disturbing that given solar minimum AND piddling ENSO signal, 2020 should have come in well below 2016 despite 4 more years of incremental warming since 2016, but that's for another rant.) 2020 is nowhere near +2.5C > preindustrial GMT, yet September minimum ASI Area is already well below 4M km2 (and has been for a while).
Fig 4. exacerbates the confusion by showing a labeled 1979-2006 average ASI summer minimum sea ice area range of ca. 5.75M - 6.25M km2.
I think what Fig. 4 is trying to say is that IF ASI vanished in context of GMT at +2.5C, we should expect about 0.10 C additional warming due to the increased Arctic albedo (shown on the right axis). Whereas, if ASI vanishes for June - July - August when GMT is at +1.5C, then we should expect an additional 0.18 C of albedo induced warming from that cause.
So what the heck is the left Y axis referring to? I tried to help them out by guessing, "Oh, they mean average ASI Area for June-July-August at those GMT values. Thus about 6.8M km2 average ASI Area for June-July-August at 1.0C. Conveniently, glennbuck had posted just the chart I needed just below the gero post at
https://forum.arctic-sea-ice.net/index.php/topic,2975.msg286915.html#msg286915. Yes, that fits.
But then why does the label in Fig 1A say "
Minimum Arctic sea ice area (observations) average 1979-2006"?
Those values are the June-August average, not the average of the summer minima. And what does it add to this chart except confusion?
Correct me if I'm wrong. Maybe I'm too dumb or tired to understand what they are saying. But I think it is the other way around. It is the authors' responsibility to communicate clearly, a task at which this article fails, and worse than that it very easily leads to gross misrepresentation to, and misunderstanding by, the reader.
The ASI situation is truly bad and getting worse. But the entire 3 month period of June-July-August is not going to be ice-free in the 2030-2050 time frame.
Conversely, summer minimum ASI Area is already well below 4M km2 at our present +1.1C, so there is no way that September minimum ASI Area at +2.5C GMT will be near 4M km2. There won't be ANY September ASI Area at 2.5C GMT over preindustrial.
At least the fallacies balance each other. But leading the reader to counteracting fallacies is not good enough, in fact it's a mess.