Heat and Climate: Some Basics

In a recent discussion heat and transport has become a point of contention. The relationship of heat of a thing (the ground, or you in a sleeping bag … or more distantly the temperature of your coffee in that thermos) depends on a few parameters. At equilibrium (not your coffee cup any more) heat transfer in equals heat transfer out. The earth, radiated at the sun, is (basically) at a time averaged equilibrium. The claim of the global climate warming crowd is that additional insulating effects raise the temperature. How does this work if the energy in still equals the energy out? Well, to first order, the energy flowing out depends on two factors, the first being the difference in temperature between the two regions and a factor dependent on the geometry of the interface and the heat conductivity of the interface. If you add insulation (reduce the heat conductivity of the interface) then to have the same amount of energy flowing out the heat differential has to be larger, i.e., in bed when you add blankets you warm up (the heat differential between outside the bed and snug in the covers rises).

It has been claimed recently (and this needs substantiation) that wind farms change the turbulence of the air in the region around them, decreasing the efficient mixing of air between low and high altitudes, i.e., decreasing their effectiveness at heat conductivity. Hence the delta T rises (the ground temp) rises in that region. This change in conductivity is what drives the temperature change at the ground. The suggestion is, that then if wind farming becomes a non-trivial fraction of the earths cover this is just the same problem as adding greenhouse gases, the result is increased global average temperatures. The same people who thing global warming is problematic should be concerned about this possibility for the same reasons. Those who are not concerned of course, should not use this as an objection against wind farming.

2 Responses to Heat and Climate: Some Basics

  1. Except the one theoretical ‘what if’ study done basically found covering the earth with wind farms would raise temps in some areas and lower it in others. Assuming, though, that large use of wind farms could produce global warming, the question would then have to be what threshold of windfarming would have to be to produce global warming equal caused by greenhouse gasses? If that threshold is 20%, say, then there’s not much of a case to object to wind farming….we are far from 20% coverage of the earth’s surface with windmills. Even if it was 2%, not much cause to object….

  2. Boonton ,
    You’re working hard making points for the wrong side. Let’s see,

    If that threshold is 20%, say, then there’s not much of a case to object to wind farming….we are far from 20% coverage of the earth’s surface with windmills. Even if it was 2%, not much cause to object….

    So, basically what your saying is that windfarms are OK as long as they don’t produce significant fractions of our energy. Kinda like what the CO2 guys say about oil and coal, eh?

    … would raise temps in some areas and lower it in others.

    You’ve not given any credible mechanism for how it cools anything. See the blanket example, no cooling of the person not under the blanket.

    I’m thinking after a short period of time the room outside the blanket is cooler than it otherwise would be if the person didn’t have the blanket it. You’re saying after a long period of time the room will settle to an equilibrium where everything is the temp. it would be *except* for under the blanket. The blanket creates a type of bottleneck on the flow of heat from the body to the room to the window and walls where it eventually escapes into the wider world.

    But consider someone outside the room measuring the heat that is escaping. After a long period of time, when everything has come to an equilibrium, he notices that the heat escaping the room is exactly what would be expected from a room with exactly one human body radiating inside of it. He can’t tell from outside whether or not the person is under a blanket, correct?

    “A long time” is the time it takes you to come to a steady temp under the bad, probably 15 minutes. But yes, he can’t tell.

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