A recent thread comment illustrates how the global warming PR campaign has installed a bogus climate paradigm in public awareness: The Supremacy of Infrared Radiation. In a discussion about clouds and the Arctic, this comment appeared:
I disagree with the comments that clouds at the poles should cause cooling.
In general the earth absorbs heat from the sun near the equator and expels it near the poles via up welling radiation. A low humidity clear sky near the poles allows most gray body radiation from the ice/oceans/land to emit directly to space. Clouds at the poles would interfere with that process and the poles would warm thus melting the ice faster. And in a general sense, that is what we’ve seen over the last 40 years. (linked to a graph of declining ice extent since 1979).
Heat Transfer Mechanisms
It takes some work to untangle the problems with this statement. Because it is true that earth’s climate system takes in solar energy mostly at the equator, which is then transported and expelled mostly at the poles. The myopia is in the notion that this is a purely radiative heat transfer. The misconception arises from confusing the view from the top of the atmosphere (TOA) with the view at the surface where we live. The TOA energy balance is purely radiative. Incoming: Short Wave (SW) in, minus Outgoing: (SW) reflected/scattered out, and minus Long Wave (LW, mostly Infrared) emitted out.
Nearer the surface, the movement of energy is dominated by other more powerful heat transfers: Conduction (from warm to cool by direct contact), Convection (air moving from warm to cool objects) and Latent Heat (water changing phases from ice to liquid to gas and back again). These processes move massive amounts of energy upward from the surface toward the nearly absolute cold of space. IR active gases, mainly H2O and the minor trace gas CO2, do absorb and re-emit some LW energy, but at a scale orders of magnitude less.
Polar Heat Exchanges
The comment above attributes warming in the Arctic to the radiative properties of H20 in clouds. There is no claim that CO2 is a factor, since it acknowledges that clear dry skies offer no significant impediment to the cooling processes. But do water vapor and clouds delay cooling in the Arctic?
While it is true that moist air in the tropics makes for mild evenings after sundown, the Arctic situation differs. There is a short season when the summer sun shines, and most of the year is dark and extremely cold.
Most people fail to appreciate the huge heat losses at the Arctic pole. Mark Brandon has an excellent post on this at his wonderful blog, Mallemaroking.
By his calculations the sensible heat loss in Arctic winter ranges 200-400 Wm2.
As the diagram clearly shows, except for a short time in high summer, the energy flow is from the water heating the air. Transfers by latent heat are in addition to the above.
For a long time I misinterpreted the meaning of charts like the current one below from DMI:
Those are air temperatures, and if they are above average, it means that the water is losing more heat than past normals. It’s not that warmer air causes ice melt, but the other way around: Oceans are always moving heat, and more open water means more heat loss into the air, resulting in higher air temperatures, though still way below zero most of the year.
For comparison, look at the same chart from 1977 when ice extent was much higher the entire year:
So if there is to be any warming effect on ice formation from clouds, it can only happen in peak summer, the precise time when their shading effect exceeds any radiative warming. And the existence of clouds indicates moisture in the air which came from the ocean evaporating.
The myopic focus on radiation and air temperatures leads into a false analogy: thinking the Arctic is a kind of refrigerator. I explained in some detail why this is not so: Arctic Is Not a Refrigerator
If one wants to use the refrigerator analogy in relation to earth’s climate, at least do it correctly as Dr. Salby does:
From Physics of the Atmosphere and Climate, pg.82
A closed system that performs work through a conversion of heat that is absorbed by it is a heat engine. Conversely, a system that rejects heat through a conversion of work that is performed on it is a refrigerator.
In Chap. 6, we will see that individual air parcels comprising the circulation of the troposphere behave as a heat engine. By absorbing heat at the Earth’s surface, through transfers of radiative, sensible, and latent heat, individual parcels perform net work as they evolve through a thermodynamic cycle (2.13). Ultimately realized as kinetic energy, the heat absorbed maintains the circulation against frictional dissipation. It makes the circulation of the troposphere thermally driven.
In contrast, the circulation of the stratosphere behaves as a radiative refrigerator. For motion to occur, individual air parcels must have work performed on them. The kinetic energy produced is eventually converted to heat and rejected to space through LW cooling. It makes the circulation of the stratosphere mechanically driven. Gravity waves and planetary waves that propagate upward from the troposphere are dissipated in the stratosphere. Their absorption exerts an influence on the stratosphere analogous to paddle work. By forcing motion that rearranges air, it drives the stratospheric circulation out of radiative equilibrium, which results in net LW cooling to space.
Stratosphere = Refrigerator