While this article is encouraging when looking at the title, they are still pushing that “ice-free summer” meme.
A late-winter expansion of Arctic sea ice is a good example of ice-forming dynamics that could keep the Arctic from hitting a “tipping point” in the near future.
Some scientists have predicted that rising temperatures could create a runaway feedback loop in the Arctic. Sunlight-reflecting ice sheets would give way to sunlight-absorbing water, driving up temperatures and melting even more ice. The Arctic climate would change so dramatically that winter ice couldn’t form again, producing planet-wide ripples in weather patterns.
But some research suggests that other, previously underappreciated forces may stabilize the melt before it’s complete. The Arctic will soon be ice-free in summer, and winter ice will decline, but it won’t suddenly become permanently ice-free.
“Everyone thought there would be a tipping point,” said Dirk Notz, a Max Planck Institute climate scientist. “But that’s too simple.”
…
Tipping-point evidence is stronger for western Antarctica than Greenland, said Notz. But even the absence of a tipping point wouldn’t necessarily be reassuring. “It doesn’t mean Greenland won’t melt away,” he said. “It just means it will happen gradually.”
Read More http://www.wired.com/wiredscience/2010/04/polar-ice-review/
Polar Sea Ice
Dwindling Arctic sea ice and crumbling Antarctic ice sheets are now a common sight. Whether they signal an impending tip, with rapid melts causing Earth’s seas to inundate heavily-populated coastal plains, is debated.
The process appears to accelerate itself: Warming ice melts, which exposes darker areas, causing local temperatures to rise further. But in the Arctic, another feedback may stabilize the ice, wrote Max Planck Institute meteorologist Dirk Notz in PNAS. Though most of the ice “will disappear during summer,” much of it will re-freeze in the winter. Arctic sea ice loss “is likely to be reversible if the climate were to become cooler again.”
But Notz is less optimistic about Antarctic sea ice, its undersides heated by eddying Southern Ocean currents. And the West Antarctic and Greenland ice sheets have shrunk suddenly at least twice in the last several million years, a behavior that’s backed up by climate models. It’s “well possible that a tipping point exists for a possible collapse” for those sheets, wrote Notz. It could “render the loss of ice sheets and the accompanying sea-level rise unstoppable beyond a certain amount of warming.”
Climate ‘Tipping Points’ May Arrive Without Warning, Says Top Forecaster
From a UC Davis press release
Though, my favorite environmental tipping sign is this one :
And one small point that was in their article was the statement, that this doesn’t have anything to do with today’s climate.
Well they actually said this:- “”” While the findings do not directly bear on current global warming, they highlight the complexity of Earth’s climate system …. “””
They said that, right before they said what you posted above; funny how you missed that small tipping point.
“”” Rob (11:10:19) :
Can someone please point me to a site that shows how many and where the REAL thermometers are that are RECORDING the Artic temperatures (that we continually hear are rising) I am sceptical that the Artic is warming but would like very much to have good data to understand how such claims are made. Thanks “””
Don’t have a site Rob; but I believe that at the 19/20th century boundary it was 12 real actual thermometer stations; well that was for their definition of the Arctic, which is >+60 deg lat.
This number gradually wandered up to about 86 if I remember correctly; and then it started to fall to something like 72; and I think that happened along with the collapse of the Soviet Union.
Now I could be wrong on those numbers; but those are about what i remember from the article that mentioned that.
Phil will know the real numbers.
Don’t quite see how 12 equates to 72 ; well other than a factor of six; but that is just accidental I’m sure.
So how do you actually measure earth’s albedo? Just what is it anyway ?
It has always been my understanding, that albedo measures the fraction of the total solar insolation intercepted by planet earth, that gets reflected from somewhere, and routed back out into space, so that it has zero effect on the energy balance of the earth. Well the actual amount that is reflected affects the amount that “lands” on earth and contributes energy somehow.
That means that albedo, represents solar spectrum radiation; which may be somewhat modified by a non constant spectral reflectance of various surfaces that make up earth; but it does not include energy that arrives at 6438.4696 Angstrom units wavelength; and somehow exits at 10.1 or even 15 microns wavelength.
So how do you measure that.
Let’s consider the earth being at an equinox position in solar orbit, so the axis is tilted roughly at right angles to the radius to the sun, and the visible sun is on the horizon at both poles. Well actually the entire disk of the sun would be visible above the horizon at the poles because of atmospheric refraction, and the center might be as much as one degree above the horizon.
So we have somewhat more than half of the earth simultaneously irradiated by solar energy; maybe 182 degrees out of 360 or more.
Now at the north pole, and south pole, you have ice/snow in both places (highly likely), and the surface is not optically flat and parallel to the mean earth surface; so the “grazing” angle reflected light from that snow ice, is actually impinging on surfaces with every possible angular orientation, so the reflected light is likely to have at least a Lambertian (cosine) angular distribution, and it could be nearly isotropic.
So that means that light reflected from the poles, can be backscattered towards the direction of the sun, or sent straight up towards the zenith; or forward scattered towards the darkness of space; so it will illuminate the entirety of space out there in the midnight sky.
Now actually, this same geometry really exists, anywhere in the earth orbit about the sun; not just at the equinox position; I just wanted to have the axis tilt in a known direction.
So even though earth is illuminated only over slightly more than a hemisphere; it actually reflects sunlight over 4 pi steradians.
So now where are you going to put your radiometer to simultaneously observe that complete 4pi steradians of space to measure the total reflected energy from the earth.
Now don’t tell me you are going to do a moon bounce, and measure what reflects off the moon.
The earth is essentially a point source as seen from the moon, so the only thing you can read at the moon’s surface, would be the axial (zenith)Radiant Intensity of the earth.
Well if you had a nice telescope, you could focus in on points on the earth, out to the limb, and make radiance measurements; but only of the backscattered light.
I suppose if you were on a satellite, that you could steer into any position in space above the earyth, you could map the radiant intensity or radiance over the complete earth and 4pi space; but you wouldn’t be able to do that all at once everywhere.
So you couldn’t keep up with cloud changes by the minute as they come and go; and it might take you some effort to even keep up with the changes in ice/snow cover, and seasonal greenery changes.
If somebody has a plot of the average 4pi radiant intensity distribution; of the earth albedo reflections; or of the radiance at all points over the earth (average) it would be interesting to see what it looks like.
I imagine that is something that is in some climate text book somewhere; or maybe a PhD thesis.
George E. Smith (10:39:23) :
Well let’s see now; ice is white; high albedo, and open water is black; low albedo.
And ice extent is 85 % black water and 15 % white ice.
So howcome most of that picture is whie rather than black. I see very little black mixed in there with the white areas. Even the mush in that tongue at the bottom is mostly white.
At this time of year most of the sea ice area is ~90+% coverage with a ‘fuzzy’ edge, the threshold chosen to designate the edge is 15% (or 30% at this time of year it makes little difference because of the steep dropoff).
“”” Phil. (06:56:18) :
George E. Smith (10:39:23) :
Well let’s see now; ice is white; high albedo, and open water is black; low albedo.
And ice extent is 85 % black water and 15 % white ice.
So howcome most of that picture is whie rather than black. I see very little black mixed in there with the white areas. Even the mush in that tongue at the bottom is mostly white.
At this time of year most of the sea ice area is ~90+% coverage with a ‘fuzzy’ edge, the threshold chosen to designate the edge is 15% (or 30% at this time of year it makes little difference because of the steep dropoff). “””
Well that of course was my point Phil; although some of these official data sets may have 15% coverage as a criterion; actual photographs, will often reveal a somewhat different viewpoint. Such as for example; that picure of a virtually completely snow covered British Isles; not long after a proclamation of future extinct species status for snow in Britain.