Saturday, March 05, 2016
"Old sooty material"! A change off CO2
Warmists are always telling us that Greenland ice is melting and it's all due to CO2 in the air. But below we read that "Old sooty material" in the ice is the culprit
Greenland's snowy surface has been getting darker over the past 20 years, absorbing more heat from the sun and increasing snow melt.
That's the conclusion of a 30-year study of satellite data, which found that the darkening and melting have accelerated due to 'feedback loops'.
The trend is set to continue, with the surface's reflectivity - or albedo - decreasing by as much as 10 per cent by the end of the century, researchers said.
The findings have global implications, because fresh meltwater pouring into the ocean from Greenland raises sea levels and could affect ocean ecology.
While soot blowing in from wildfires contributes to the problem, experts were surprised to find they are not driving the change.
Professor Marco Tedesco, a researcher at Columbia University and adjunct scientist at Nasa Goddard Institute of Space Studies, said the darkening is caused by old sooty material locked below the surface of the ice sheet.
As the ice starts to melt in summer, dust and soot are exposed and darken the pristine snowy surface. Then, as the snow refreezes, the grains get larger because they become stuck together.
Both the old dark material and the new grainier snow decrease the reflectivity of the ice sheet – a property called the albedo – particularly in the infrared range.
This means that more solar radiation is absorbed, leading to faster melting in a potentially-disastrous feedback loop.
The study used satellite data from 1981 to 2012 and found that, at first, there was very little change.
But from about 1996, the darkening increased and the ice began absorbing about two per cent more solar radiation per decade.
At the same time, summer temperatures in Greenland increased by about 0.74°C per decade, due to the effects of the North Atlantic Oscillation.
This is a natural large-scale weather cycle bringing warm, moist air from the south.
The pattern shifted back again in 2013 to 2014, but by then the ice sheet had become more sensitive and surface melting spiked again in 2015.
'It's a complex system of interaction between the atmosphere and the ice sheet surface,' Professor Tedesco said.
'You don't necessarily have to have a "dirtier" snowpack to make it dark.
'It might look clean to our eyes but be more effective in absorbing solar radiation.'
'Overall, what matters, it is the total amount of solar energy that the surface absorbs. This is the real driver of melting.'
Posted by John J. Ray (M.A.; Ph.D.).