John McKerral, one of the climate deniers who regularly adorn the Canberra Times letters page, has contributed a new dollop of facepalmworthiness. This appeared in the 5 September 2012 print edition:
Ice melt fantasy
Once again George Monbiot (“Wealth melts along with ice“, Forum, September 1, p7) has thrilled us with his fantasy scaremongering.
Monbiot wrote that as the Arctic ice melts, the sea, darker than the ice, will absorb sunlight that would have been reflected had the ice not melted. But sunlight arrives at an extreme angle to the surface that far north and is reflected back to space. Now here is some high school physics: light impinging upon water at a large enough angle (from the perpendicular to the surface) will not be absorbed, but will be reflected totally.
If the Earth was flat this would not happen as the angle of incidence, being less, would not result in it being reflected. However as most of us know, even sceptics, the Earth is a sphere and the angle that such light strikes the water that far north is such that it is reflected instead of absorbed. That whole article was based on a false premise and is therefore nonsense.
J. McKerral, Batemans Bay, NSW
… to which I replied:
According to J. McKerral (Letters, 5 Sept), “high school physics” says that sunlight shining on the Arctic ocean will be “reflected totally” because it arrives at a low angle, and so the extraordinarily rapid melting of Arctic sea ice is not a problem.
As a self-proclaimed “sceptic”, you would expect him to check this bizarre claim before proclaiming it to be true. And, of course, it’s completely false: while reflection naturally reduces the amount of radiation absorbed by water at low angles, it’s nowhere near zero in the Arctic Ocean in summer.
Fresnel equations show that with the sun 30 degrees above the horizon – typical for Arctic summer – water reflects less than 10% of incoming radiation, whereas sea ice reflects 30-70% of incoming radiation.
So the climate scientists saying that Arctic sea ice melt is a problem are right. Whoda thunk it?
It’s amazing that so-called climate sceptics – those intellectually dishonest traders in misinformation, distortion and outright falsehoods – have sunk so low in their desperate fight against reality.
What’s worse is that they continue to have sympathisers among many old white males in politics and the media. History will judge these people harshly long after they are gone.
Matt Andrews
Basically, McKerral’s foolish statements were wrong because they took a real effect (the increase in the albedo of water as the angle of the sun lowers) and utterly distorted it into falsehoods: that a low sun angle means radiation is “reflected totally”.
I used the figure of 30 degrees above the horizon as being a reasonable value for the Arctic in summer, because the Arctic Circle sees the sun at 47 degrees above the horizon in mid summer, and the North Pole at 23.5 degrees.
You might find this graph showing how the albedo of water changes with sun angle interesting; it’s referred to in the Wikipedia article on albedo (reflectivity). So when the sun is overhead the albedo is very low – only about 3%. When the sun is right on the horizon (at 90 degrees to normal) the albedo is nearly 100%. At 60 degrees from normal (30 degrees above the horizon) the average albedo is around 7%. Only when the sun drops below about 20 degrees do we see dramatic increases in albedo.
#1 by Oxford Kevin on September 5, 2012 - 8:52 pm
Quote
The other ignored issue is that the surface of the water is not mirror flat, but is made up of small or large waves/swell. The consequence is that the surface that the light is reflected off or absorbed through is more likely to be one with a lower angle of incidence.
#2 by Owen on September 5, 2012 - 10:04 pm
Quote
And lets not forget that the ice retreats from the edges.
Ie; The lower latitudes where a change from ice to open water will cause maximum increase in heat absorption are the areas where the ice will disappear fastest (and already has, in many cases).
Also interesting to note (from the excellent Wikipedia article, thanks for the link) that snow has a higher albedo than sea ice.
Long term ice that has received a proper covering of snow is the best reflector, newly formed sea ice at the start of winter is less effective. And of course, snow cannot settle on the open sea. Snowfall hitting regions that are no longer frozen is not benefiting us in the way it used to..
.. another good example of how some climate systems feedback to accelerate the change.
And since the polluting deniers seem to think maintaining a high albedo is important, can they square that argument with the fact that when snow and ice gets polluted, covered in dust, sploshed with oil, it’s albedo drops rapidly?
http://www.atmos.washington.edu/sootinsnow/
#3 by klem on September 5, 2012 - 10:59 pm
Quote
And lets not forget that sea ice measuements only go back to 1979. We have no idea if today’s low Arctic sea ice extent is unusual in any way.
cheers
#4 by Owen on September 6, 2012 - 1:10 am
Quote
@klem;
Nothing to forget..
..that 1978 line only applies to ice thickness, not surface area .. and even then it is a manipulation.
Let me help with your flawed history:
Current form of satellite records (radar mapping of ice thickness and volume) from 1978
Satellite records of ice extent actually begin in 1973
Systematic records (commercial and national) from the 1950’s
Other records from whalers and shipping data, limited governmental records etc: 1930’s
Explorers; 1880->1920’s took specific measurements and made good records.
And there is sporadic scientific, commercial and cultural record keeping for hundreds of years before that.
Specific historical records identifying the edge of the ice sheets go back a long way. This info had commercial, practical and cultural value to many people.
Please be assured that the extent of ice cover we currently see is the lowest in several hundred years of records, by a considerable margin. And it is still melting.
#5 by matt on September 6, 2012 - 12:05 pm
Quote
#1 Oxford Kevin: an excellent point; I should have mentioned this. In the real world this makes a huge difference. The Fresnel curve is for perfect reflection conditions (completely still water, no atmospheric scattering at all); of course, the ocean is rarely mirror-smooth… and consequently the real reflection of radiation is much lower than these equations show.
#2 Owen: good points re edge dynamics and snow: snow albedo is ridiculously high and, as you say, doesn’t happen on water 🙂
#3 klem: Actually we do have quite a number of lines of evidence which show us something about sea ice extent before satellite observations started, as Owen points out at #4. See the reconstruction graph (with error bars) in this Skeptical Science article: “Melt Unprecedented in Last 1,450 years”. Also some human-friendly summaries in posts at the Arctic Sea Ice Blog.