For a long time now (at least six years), Willis Eschenbach has been going on about governors, forcing and feedback. For a long time now (at least six years), the engineers at WUWT have been pointing out where Willis gets his terminology and concepts wrong. For a long time now, Willis hasn't listened to the experts.
Willis Eschenbach maintains, despite all evidence to the contrary, that climate doesn't change. He seems to think that every time a forcing is applied, it will be met with an equal and opposite force. Today he's arguing the same thing that he's argued time and time again.
As in the past, Willis gets quite a bit wrong (archived here):
- uses the analogy of cruise control (wrongly)
- confuses positive and negative feedback
- mistakes feedback for forcing.
This article is about some fundamental concepts in climate science, mainly for the benefit of people new to the subject. (You'd think deniers at WUWT, who've been writing about climate for years, would have grasped these concepts by now. But many of them, like Willis Eschenbach, haven't.)
Forcing and feedback - positive and negative
So how about some clarification of the terminology. In this article, I'm using simplified examples to illustrate the main points. It can take a bit to get your head around at first if you're not used to the jargon. It's really not that difficult to grasp, once that light bulb turns on.
Forcing - something that causes a change in a particular direction. In climate, the primary cause of a rise or fall in global temperature.
- Positive forcing - an increase in greenhouse gases is a positive forcing in that it means less long wave radiation from the surface will go straight out to space, causing temperature to increase
- Negative forcing - an increase in aerosols (of particular kinds) are a negative forcing, in that it reflects more incoming solar radiation, causing temperature to drop.
Feedback - something that is caused as a secondary effect from what is forced. In climate, the rise or fall in temperature causes something else, which in turn acts to exacerbate or dampen that rise or fall in temperature:
- Positive feedback is something that, in the temperature example, causes the temperature to go up even more. It amplifies the forcing.
- Negative feedback - in the temperature example, causes the temperature to not rise quite as much. It reduces the forcing. It means the temperature doesn't rise as much as it would without the negative feedback. It doesn't cause the temperature to fall. What it does is dampen the signal, not reverse it.
When the sun increases energy, the temperature of earth rises. This rise in temperature causes other things to happen. Because these 'other things' will only happen because of the forcing, they are known as feedbacks. They are a feedback response to the rise in temperature. Here is a positive feedback to the increase in temperature - relating to water vapour:
- More water will evaporate, which may lead to more clouds, which will lead to more rain and snow. If that were all, then this feedback would have no effect on temperature. The loss of heat at the surface when the water evaporated would be (almost) balanced by the release of heat up in the atmosphere when the water condensed. This on its own isn't a feedback. It neither amplifies nor dampens the rise in surface temperature. Well, almost anyway. But that's not all that happens.
- Water vapour is a greenhouse gas. More of it reduces the radiation that leaves the planet, which results in a still warmer planet. The increase in greenhouse gases (water vapour) is a positive feedback to the increase in temperature from an increase in solar radiation.
- The negative feedback would be because more clouds will reflect some of the incoming radiation, so dampen the increase in surface temperature. It wouldn't get as hot as it would without the clouds.
- The positive feedback would be because clouds pose a barrier to long wave radiation leaving the surface and heading out to space. So the temperature rise would be greater than it would without the clouds.
Willis Eschenbach confuses forcing and feedback
...the underlying climate paradigm is that the forcing controls the temperature, such that a change in forcing causes a change in temperature.Yes. By definition, a change in radiative forcing of a system will cause a change in temperature, all other things being equal. When there is an increase in energy in the system it will heat up. A drop in energy cools the system. Willis continues:
On the other hand, I’ve proposed that there is a natural governing system regulating the temperature of the climate, a major part of which works as follows.Here Willis is confusing forcing and feedback. Willis talks about solar forcing. Solar forcing comes from outside the system. It comes from the sun itself. Any cloud response is a feedback, not a forcing. What happens on Earth will make no difference to how much solar energy is put out by the sun. In other words, whether or not clouds form will make not one jot of difference to the forcing. Changes in clouds can be a feedback (as above).
In the tropics, when it is warm, clouds form earlier and reflect away the sun to cut down the solar forcing. And when the tropics are cool, the clouds form later or not at all, which greatly increases the solar forcing.
What that means is that a change in temperature causes a change in forcing.No, he's wrong. The change in temperature can cause feedbacks. It won't change the forcing, which in Willis' example of solar forcing is the increased amount of energy hitting the top of the atmosphere. The feedback in regard to the water cycle in the tropics could be as follows, assuming an increase in solar forcing (more energy from the sun):
- More water evaporates - an increase in the total amount of water vapour in the troposphere, and a cooling effect on the ocean surface (latent heat of evaporation).
- More clouds may form - there is more water vapour to condense. This condensation would have a heating effect in the atmosphere - an almost an equal and opposite reaction to the cooling at the surface (releasing heat as water vapour condenses into water droplets).
- More clouds can reflect more sunlight - a negative feedback, dampening but not reversing the rise in temperature, it heats up but not quite as much.
- More clouds can mean less heat escapes to space - a positive feedback, exacerbating the rise in temperature - it heats up more.
- More ice will melt and less snow cover - both positive feedbacks, with less sunlight reflected back to space, and more darker surfaces exposed absorbing heat - exacerbating the rise in temperature.
And that is why I say that the current method of analyzing the climate is totally incorrect, because it assumes the causation is going the opposite direction from what is actually occurring.It's Willis who has it wrong. In his example of solar forcing, if the sun increases its output, then earth heats up. There will be feedbacks on earth in response to the rise in temperature. As long as the forcing operatres, all that those feedbacks can do is either:
- make the temperature rise even more than it would without the feedback - positive feedback; or
- dampen the rise in temperature, meaning it will rise, but not as much as it would without the feedback - negative feedback.
You'll not get a reversal or any change in the forcing itself. How could you? Earth has little to no control over the sun. The sun is much more powerful.
Same goes for adding greenhouse gases. That will result in a rise in temperature. Greenhouse gas forcing will raise the temperature. There's no escaping the fact that adding more greenhouse gases to the air will raise the temperature of the planet - the oceans and the troposphere. There will be positive feedbacks that will make the temperature rise even higher; and negative feedbacks that will dampen the rise, so it's not as great. Whatever - the net effect is still a rise in temperature.
Willis and his governors
Willis started off his article talking about governors and cruise control. He got that wrong too, as he has done before. With the biggest sub-group at WUWT being engineers, there were lots of people ready to point out his errors - as there have been on previous occasions, when Willis took just as much notice (ie none).
From the WUWT comments
Mike quotes Willis and points out some of where he goes wrong:
August 2, 2015 at 2:22 am
“A common example in our daily lives is the cruise control on your car. It increases or reduces fuel flow (positive and negative feedback) to maintain the vehicle speed near some pre-set value."
Willis , you really need to find out what the terms mean if you want to discuss this kind of thing.
Positive and negative f/b does not relate to whether the thing being driven is going ‘up or down’. A negative f/b is one which acts to counter a deviation and a positive one is one which acts to increase it further.
If a hill slows the vehicle down, the cruise control acts as a negative feedback by increasing the gas.
Mike McMillan points to a negative climate feedback:
August 2, 2015 at 5:07 am
The Stefan-Boltzmann law is a governor of sorts, increasing or decreasing radiation by the 4th power in an effort to maintain a temperature.
charles nelson is amazed by Willis:
August 2, 2015 at 2:55 am
It amazes me how many people do not understand the concept of set point and diff!
August 2, 2015 at 3:05 am
A governor is a governor. Feed back is feedback. Totally different animals. Next thing you know , people will be saying that CO2 is a control knob
To which Mike replied:
August 2, 2015 at 3:54 am
A governor is a control device that applies a negative feedback.
Paul Schnurr finds the engineer talk interesting, but still thinks Willis makes a good point. He doesn't.
August 2, 2015 at 4:51 am
It’s interesting to learn how engineers define and use “positive” and “negative” when discussing feedback but for laymen Willis’ example is clear no matter how feedback is defined: a changing temperature can change forcing to one which acts to reverse the temperature change. At least that’s how I see it.
Related HotWhopper articles
- Putting the foot to the floor - with Willis Eschenbach again - July 2015
- Wondering Willis Eschenbach's Thunderstorm at WUWT - October 2013
- Denier Weirdness: Wondering Willis Eschenbach wonders does "an ice age cometh"... - October 2013
- Wondering Willis' Original Weather Hypotheses - December 2013