By Stephen Wilde

The oven analogy was suggested to me by a firm proponent of anthropogenic climate change. The idea was that if one increases the insulation around an oven then it will reach a higher equilibrium temperature for the same energy input. Obviously the suggestion was that extra human greenhouse gases are analogous to extra insulation around an oven.

At first thought that seemed to be a fair and reasonable analogy but I did feel that it did not quite fit the Earth’s climate system and it took me a few minutes to work out the flaw. The Earth may be like an oven but because Earth is exposed to space with a flow of energy out to space it is more like an oven with the door open.

So, the heating element represents the sun, the sides, top and base represent the Earth’s oceans, the air in the interior cavity represents the air around the Earth, the flow of air in and out of the open door represents the movement of the air around Earth from surface to space as it transfers energy upwards.

The Implications:

1)The heating element of an oven provides the source of energy that warms up the sides, top, base and the air in the cavity. As the temperature rises towards equilibrium air moves in and out more rapidly until equilibrium is reached between the energy flow from the heating element and the flow of energy out through the open door. Unless the heat is turned up the oven will get no warmer. At that point the heat of the oven is contained primarily in the metallic or other compounds that comprise the sides top and base of the oven. The amount of heat energy contained in the air in the oven is trivial and is constantly being moved out of the oven by the circulation of the air.

2)The triviality of the heat energy in the air is important. If one were to somehow change the conductive characteristics of the air in the oven it would have no significant effect on the equilibrium temperature of the oven. However if one were to change the conductive characteristics of the sides, top and bottom then the change in equilibrium temperature would be significant.

3)So it is with the Earth. The equilibrium temperature is primarily set by the power of the sun combined with the conductive characteristics of the oceans. The contribution from the conductive characteristics of the air around us is insignificant and the contribution from a tiny component wholly irrelevant. Furthermore the energy content of the oceans seems to be in constant flux via multi decadal cycles in each ocean that change the rate of solar energy flow from ocean to air and thereby change the temperature of the air globally to an extent that regularly swamps any changes that could ever be induced by changes in the air alone.

Summary:

1) The greenhouse effect of the air (the definition of atmosphere should include oceans for the purposes of this discussion) depends on the ocean only as a means of getting lots of water vapour into the air. However the greenhouse effect in the air is just an expression of the slowing down of the transmission of energy through the air and water vapour is the main cause of that slowing down. The air is only one section of the whole process that involves energy flowing from sun to oceans to air to space. The air should not be viewed in isolation. It is the slowing down of the transmission of solar energy through the entire planetary system of Earth that sets the equilibrium temperature of the planet.

2) As a separate process there is a slowing down of the transmission of energy through the oceans. That is the Hot Water Bottle Effect.

3) The slowing down effect in the oceans is so huge that it renders the slowing down effect in the air insignificant so that the equilibrium temperature of the planet is set by the oceans and not the air. Read more here.