The Illusion of a Sensitive Climate System: A Stovetop Demonstration

April 10th, 2010 by Roy W. Spencer, Ph. D.

(edited for clarity, 8:15 a.m.CDT April 10)

Whether it is the Earth’s climate system experiencing warming, or a pot of water being placed on a warm stovetop, the fundamental basis of why the temperature of something changes is the same: If energy is being absorbed faster than it is being lost, then warming will result.

This is illustrated in the following two plots, which show that imposing such an “energy imbalance” on a pot of water (or on the Earth’s climate system) causes warming which is at first rapid, but then slows as the system reaches a new state of energy equilibrium where the rate of energy loss by the system increases to match the rate of energy gain. Once these two flows of energy once again become equal, the temperature stops changing.

In the context of global warming, more CO2 added to the atmosphere from humanity’s burning of fossil fuels slightly reduces the Earth’s ability to cool to outer space through infrared energy loss, contributing to the Earth’s so-called ‘greenhouse effect’. This “heat radiation”, by the way, is also one of the energy loss mechanisms for a pot of water on the stove.

In global warming theory, this increase in the greenhouse gas content of the atmosphere causes an energy imbalance, which then causes warming. The warming then increases the rate of infrared energy loss until energy equilibrium is once again restored — but now at a higher temperature. This is the basic mechanism behind the theory of manmade global warming.

Returning to the above plot, if we know (1) the amount of energy imbalance imposed upon the system — whether a pot of water or the Earth — and we know (2) how much the system then warms as a result, we then know the temperature “sensitivity” of the system to an energy imbalance.

For instance, if a small energy imbalance leads to a large temperature change, that is called high sensitivity. This is how all climate models now behave, and is the basis for Jim Hansen’s and Al Gore’s fear of a global warming Armageddon.

But alternatively, if a large energy imbalance causes only a small temperature change, then that is called low sensitivity, which is how I, MIT’s Dick Lindzen, and a minority of other climate researchers believe the climate system behaves.

I believe that climate researchers have fooled themselves into believing that the climate system is very sensitive. The reason why is related to a real-world complication to the above simplified example: when we compare a warm year to a cool year in the real climate system, we are NOT looking at the equilibrium response at one of those temperatures, to an energy imbalance imposed at the other temperature. That would be a very special case indeed, and it is one that never happens in the real world.

To see what usually happens in the real climate system, let’s return to the example of a pot of water on the stove. Imagine we keep turning the stove up and down, over and over. This will result in the water warming and cooling as the temperature responds to the ever-changing energy imbalance of the system.

Now imagine we have measured both the energy imbalances and the temperatures over time so that we can compare them. If we compare all of the times when the water was warmer to all of the times that the water was cooler, what we will find is that the difference in energy balance between the warmer and cooler temperature states is very nearly the same.

And if a big temperature difference corresponds to only a small change in energy imbalance, this then ‘looks like’ a highly sensitive system…even if the system has very low sensitivity!

If we just turn the stove up once, and then let the system come to a new state of equilibrium, then we really can measure the sensitivity of the system. But if we keep turning the stove up and down, this is no longer possible.

In the real world, the climate system is almost never in a state of energy equilibrium. Chaotic changes in the average cloud cover of the Earth are like the stove being turned up and down, since the amount of sunlight being absorbed by the climate system is “turned up and down” by the ever-changing cloud cover.

As a result, satellite measurements of the Earth energy imbalance will show that there is, on average, only a small energy imbalance difference between warm years and cool years. This gives the illusion of a sensitive climate system, even if the system is very IN-sensitive.

Again, the illusion arises because we try to measure the sensitivity of the climate system based upon a false assumption: that different temperature states of the Earth correspond to a change from energy dis-equilibrium at one temperature, to energy equilibrium at the other temperature. This is almost never the case…yet it IS the only case in which the sensitivity of the system can be measured! Researchers up to this point have been trying to diagnose climate sensitivity from observations of natural climate variations based upon a false assumption.

This issue will be addressed at length, along with theoretical model demonstrations, in our new research paper which has just been accepted for publication in the Journal of Geophysical Research.

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