I medierna har ju rätt spekulativt larmats om att Grönlands is pga ökande smältvattenmängder kan glida ut i havet. Ökad ishastighet konstaterar man nu är ett kortvarigt fenomen på sommaren, där man istället registrerar att isen saktar in. (Förresten hade ju medeltiden och holocena otimum 2-4 grader varmare klimat på Grönland, och senaste decenniet har haft fallande temperatur. Någon fara lär inte ha funnits.)
Ur New Scientists "Greenland ice sheet slams the brakes on":
"Greenland's mighty ice sheet has enough water locked away to raise global sea level 6.5 metres were it to melt. Each summer, vast lakes of meltwater form on its surface. The water seeps through cracks in the kilometer-thick ice to bedrock, where it acts as a lubricant. The sheet can move up to twice as fast in the summer, when meltwater is flowing, as when it is not.
Many fear a positive feedback loop, whereby the accelerating flow will bring more ice down out of the mountains and toward warmer temperatures near sea level. Roderik Van De Waal and colleagues at Utrecht University in the Netherlands now say there is no evidence this will happen.
They looked at how meltwater has correlated with the speed of ice flow at the western edge of the sheet, just north of the Arctic Circle, since 1991. They found that meltwater pouring down holes in the ice – called "moulins" – did indeed cause ice velocities to skyrocket, from their typical 100m per year to up to 400m per year, within days or weeks.
But the acceleration was short-lived, and ice velocities usually returned to normal within a week after the waters began draining. Over the course of the 17 years, the flow of the ice sheet actually decreased slightly, in some parts by as much as 10%.
"For some time, glaciologists believed that more meltwater equaled higher ice speeds," Van de Waal says. "This would be kind of disastrous, but apparently it is not happening." "
Rapporten i Science, vol 321 p 111.
Andra bloggar om: vetenskap, miljö, klimat, klimatet, alarmism, glaciärer, is, Grönland, klimatförändringar, växthuseffekten