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.
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.