Wow, this is cool. H/t Felicity Barringer at the New York Times.
I find these sorts of papers delightful because they take a problem that has engaged many brilliant people -- Why is the Arctic melting faster than climate models suggest it should? -- and suggest a simple correction, backing up that intuition with data.
In this case, the powerfully simple idea is ice is not totally opaque. As anyone who has ever looked at a piece of ice knows, thin ice lets more light through, thicker less. So with the aid of sensors under the ice, the authors have shown that the thinning of the ice sheet, the melting and re-freezing, under global warming, results in more thin ice and less thick ice. Boom! Another positive feedback; more energy is absorbed, the Arctic warms fast and the ice melts faster.
Seems almost too basic, doesn't it? Elegant idea, elegant demonstration.
Although, don't expect this to be the last such correction. Last time I checked the GCMs still don't get the current changes right (apparently a resolution problem). Also, if it's the case that Jennifer Francis et al. are correction about the jet, some of the resultant funny weather seems likely to be feeding back onto the ice. And ho could we forget this year's proof that the models had gotten ice thickness/volume wrong? More on that list?
ReplyDeleteOh no, I don't expect this to be the end. It's just another step in the direction of modeling the climate effectively.
DeleteLeaving model performance out of the equation we have:
ReplyDelete1) The Summer Arctic Dipole, which is accelerating the seasonal loss of ice in June July and August.
2) Increased absorption of sunlight as first year ice (FYI) has a lower albedo than multi-year ice (MYI), the energy by the ice gained is almost 1/3.
3) Increased insolation through the ice.
Factor 1 is hard to quantify.
Factor 2 900MJ/m^2 cumulative energy gain for MYI, 1200MJ/m^2 over the melt season, June to Sept is around 90 days, 1 watt is 1J/second.
90 days = 90 X 24 X 60 X 60 = 7,776,000 seconds.
Therefore as the difference in cumulative energy gain per m^2 is 1200 - 900 = 300MJ/m^2. That figure divided by the number of seconds in a season...
300MJ/m^2 implies 38.6W/m^2 gain when ice cover transitions from MYI to FYI. The graphic you post implies about 1W/m^2 for insolation through the ice.
So the solar heating of underlying water is a small factor compared to the albedo energy gain of ice. And the impact of the summer Arctic Dipole isn't known...
Correction, to be clear that's:
ReplyDelete900MJ/m^2 for MYI, 1200MJ/m^2 for FYI over the melt season.
References on this page:
http://dosbat.blogspot.co.uk/2012/09/sea-ice-albedo-changes-and-seasonal.html