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Author Topic: Arctic sea ice albedo diminishing  (Read 2563 times)

BornFromTheVoid

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Arctic sea ice albedo diminishing
« on: August 06, 2013, 12:52:30 AM »
From NewScientist http://www.newscientist.com/article/dn23994-arctic-ice-grows-darker-and-less-reflective.html#.UgAq25LCam6

Arctic ice is losing its reflective sheen. It's common knowledge that each summer, more and more of the ice melts leaving the dark waters of the ocean uncovered – a process that accelerates global warming by reducing the amount of solar radiation reflected back into space. Now it turns out that the surviving sea ice is also becoming darker and less reflective.

For the first time, a detailed analysis of 30 years of satellite data for the Arctic Ocean has quantified how much the albedo, or reflectivity, of Arctic ice is diminishing. Aku Riihela of the Finnish Meteorological Institute told New Scientist he estimates that darker ice means the Arctic Ocean's albedo at the end of the summer is of the order of 15 per cent weaker today than it was 30 years ago.

The cause of the darkening, says Riihela, is partly due to thinning ice and the formation of open water fissures, and partly because in the warmer air, ponds of liquid water form on the surface of the ice. The shallow ponds on the ice can dramatically reduce reflectivity and increase the amount of solar radiation that the ice absorbs. "This shows that the increasing melt affects the inner Arctic sea ice, too," said Riihela.



The Nature abstract is here http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1963.html

Observed changes in the albedo of the Arctic sea-ice zone for the period 1982–2009

The surface albedo of the Arctic sea-ice zone is a crucial component in the energy budget of the Arctic region1, 2. The treatment of sea-ice albedo has been identified as an important source of variability in the future sea-ice mass loss forecasts in coupled climate models3. There is a clear need to establish data sets of Arctic sea-ice albedo to study the changes based on observational data and to aid future modelling efforts. Here we present an analysis of observed changes in the mean albedo of the Arctic sea-ice zone using a data set consisting of 28 years of homogenized satellite data4. Along with the albedo reduction resulting from the well-known loss of late-summer sea-ice cover5, 6, we show that the mean albedo of the remaining Arctic sea-ice zone is decreasing. The change per decade in the mean August sea-ice zone albedo is −0.029±0.011. All albedo trends, except for the sea-ice zone in May, are significant with a 99% confidence interval. Variations in mean sea-ice albedo can be explained using sea-ice concentration, surface air temperature and elapsed time from onset of melt as drivers.



crandles

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Re: Arctic sea ice albedo diminishing
« Reply #1 on: August 06, 2013, 12:43:02 PM »
Variations in mean sea-ice albedo can be explained using sea-ice concentration, surface air temperature and elapsed time from onset of melt as drivers.[/i]

They don't have to use MYI vs FYI diff?

I would have thought they should get a better fit if they did use FYI/MYI difference.

iceman

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Re: Arctic sea ice albedo diminishing
« Reply #2 on: August 06, 2013, 03:41:08 PM »
Variations in mean sea-ice albedo can be explained using sea-ice concentration, surface air temperature and elapsed time from onset of melt as drivers.[/i]
I would have thought they should get a better fit if they did use FYI/MYI difference.
Likewise.  The data series in Riihelä et. al. is through 2009, and the percentage of FYI jumped in 2008.  In view of the albedo difference between FYI and MYI relating to melt pond formation (Figure 3 of Perovitch & Poshenski 2012, as Chris Reynolds discussed at Dosbat http://dosbat.blogspot.co.uk/2012/09/sea-ice-albedo-changes-and-seasonal.html), you would expect some drop-off at the end of the Riihelä graphs.  Maybe not in May (the blue top trace in Fig. 2) before the melt ponds amount to much, but at least in June and July.  Yet those values for 2008 and 2009 are near the trendline.
   It might take a few more years of data, averaging out weather effects, to show the influence of FYI/MYI on the albedo trend.

Jim Hunt

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Re: Arctic sea ice albedo diminishing
« Reply #3 on: August 06, 2013, 05:31:59 PM »
I would have thought they should get a better fit if they did use FYI/MYI difference.

I just happened across this, from Hudson & Granskog et. al. 2013

Energy budget of first-year Arctic sea ice in advanced stages of melt

It's open access, and suggests (amongst other things) that:

Quote
The aggregate scale albedo of this younger, thinner ice was significantly lower than at Surface Heat Budget of the Arctic Ocean (SHEBA), and the transmittance was significantly higher here, despite similar pond and open water fractions.
Reality is merely an illusion, albeit a very persistent one - Albert Einstein