It's Not About Feedback

Guest Post by Willis Eschenbach

The current climate paradigm believed by most scientists in the field can be likened to the movement of balls on a pool table.

Figure 1. Pool balls on a level table. Response is directly proportional to applied force (double the force, double the distance). There are no “preferred” positions—every position on the table is equally attainable and probable.

The current climate paradigm is as linear and as mechanistic as that pool table. At its heart is the belief that the controlling equation for the future evolution of the climate is:

Forcing Change of 3.7 watts/metre^2 = 3°C Surface Temperature Change

This can also be written as:

∆T = λ ∆Q

where ∆Q is the change in forcing, ∆T is the change in temperature, and lambda (λ) is the climate sensitivity of 3°C / 3.7 w/m2 = 0.8 degrees C for each additional watt/m2 of forcing.

Everything else is claimed to average out, leaving only that relationship. The ratio between the imposed forcing and the supposed resulting temperature change is assumed to be a constant, called the “climate sensitivity”. There is much discussion as to the value of the climate sensitivity, which swirls around whether there is net positive or negative feedback from things like clouds and water vapor. According to the prevailing theory and equation, if the climate sensitivity is high, a small forcing change is said to cause a larger temperature change, and vice versa.

Me, I don’t believe that equation one bit. I discussed problems with the equation in “The Cold Equations“. For me, the idea that surface air temperature slavishly follows forcing goes against everything I know about complex natural flow systems. I cannot think of any complex natural flow system which is linear in that manner with respect to its inputs. I find it completely astounding that people actually believe that the global climate system, with all of its intricate feedbacks and forcings and resonances and chaotic nature, is that linearly simple. But that is the current paradigm for the climate, a completely linear system.

I am neither a climate sceptic, nor an AGW believer, nor an agnostic on the subject. Instead, I am a climate heretic. I think that the dominant climate paradigm is completely incorrect. I hold that there is no level pool table. I say that there is no constant “climate sensitivity”. Instead, there are preferred states. I say, and have discussed elsewhere, that the temperature of the Earth is kept within a fairly narrow range through the action of a variety of natural homeostatic mechanisms.

So what is a homeostatic mechanism when it’s at home?

The concept of “homeostat” is a more general version of the word “thermostat”. A thermostat keeps temperature the same. A homeostatic mechanism keeps something the same. A familiar version is the “cruise control” of a car, which keeps the car’s speed the same. Per Wikipedia, homeostasis is “the property of a system, either open or closed, that regulates its internal environment and tends to maintain a stable, constant condition.” Not a bad definition. It is a natural governor which regulates some aspect of the system.

The first thing to understand about climate homeostasis is that it has nothing to do with feedback. This is because in general the controlling mechanism involves a regime shift, rather than a variation in some feedback value. The current furore about the exact level of feedback in the system, while interesting, is not directly relevant, as variations in feedback are not a feature of the control mechanism.

To see why the control mechanism regulating the earth’s temperature does not involve feedback, here is the evolution of the day and night in the tropical ocean. The tropical ocean is where the majority of the sun’s energy enters the huge heat engine we call the climate. So naturally, it is also where the major homeostatic mechanism are located.

At dawn, the atmosphere is stratified, with the coolest air nearest the surface. The nocturnal overturning of the ocean is coming to an end. The sun is free to heat the ocean. The air near the surface eddies randomly.

Figure 2. Average conditions over the tropical ocean shortly after dawn. 

 As the sun continues to heat the ocean, around ten or eleven o’clock in the morning there is a sudden regime shift. A new circulation pattern replaces the random eddying. As soon as a critical temperature/humidity threshold is passed, local circulation cells spring up everywhere. These cells transport water vapor upwards to the local lifting condensation level. At that level, the water vapor condenses into clouds as shown in Figure 3.

Figure 3.  Average conditions over the tropical ocean when cumulus threshold is passed. 

Note that this area-wide shift to an organized circulation pattern is not a change in feedback. It has nothing to do with feedback. It is a self-organized emergent phenomenon. It is threshold-based, meaning that it emerges spontaneously when a certain threshold is passed. In the “wet” deep tropics there’s plenty of water vapor, so the major variable in the threshold is the temperature.

Under the new late-morning cumulus circulation regime, much less surface warming goes on. Part of the sunlight is reflected back to space, so less energy makes it into the system to begin with. Then the increasing wind due to the cumulus-based circulation pattern increases the evaporation, reducing the surface warming even more by moving latent energy up to the lifting condensation level.

Note that the system is self-controlling. If the ocean is a bit warmer, the new circulation regime starts earlier in the morning, and cuts down the total daily warming. On the other hand, if the ocean is cooler than usual, clear morning skies last later into the day, allowing increased warming. The system is regulated by the time of onset of the regime change.

Let’s stop at this point in our examination of the tropical day and consider the idea of “climate sensitivity”. The solar forcing is constantly increasing as the sun rises higher in the sky. In the morning before the onset of cumulus circulation, the sun comes through the clear atmosphere and rapidly warms the surface. So the thermal response is large, and the climate sensitivity is high.

After the onset of the cumulus regime, on the other hand, much of the sunlight is reflected back to space. Less sunlight remains to warm the ocean. In addition to reduced sunlight there is enhanced evaporative cooling. Compared to the morning, the climate sensitivity is much lower. The heating of the surface slows down.

So here we have two situations with very different climate sensitivities. In the early morning, climate sensitivity is high, and the temperature rises quickly with the increasing solar insolation. In the late morning, a regime change occurs to a situation with much lower climate sensitivity. Adding extra solar energy doesn’t raise the temperature anywhere near as fast as it did earlier.

So climate sensitivity varies … which means, of course, that the constant “temperature sensitivity” that they claim exists must be an average temperature sensitivity. Fair enough, let’s take a look at how that works.

Suppose the early morning regime and the late morning regime are the same length, maybe three hours each. In that case we take the simple mathematical average. But here’s the problem. As noted above, when it’s warm the cumulus circulation starts up earlier than usual. More hours of cumulus means lower sensitivity.

On the other hand, when the ocean is cooler than usual, the clear skies prevail for more of the morning. As a result, the average climate sensitivity rises.

In other words, in the all-important tropical region, climate sensitivity is not a constant in any sense. Instead, it varies inversely with temperature.

Moving along through the day, at some point in the afternoon there is a good chance that the cumulus circulation pattern is not enough to stop the continued surface temperature increase. When the temperature exceeds a certain higher threshold, another complete regime shift takes place. Some of the innocent cumulus clouds suddenly mutate and grow rapidly into towering monsters. The regime shift involves the spontaneous generation of those magical, independently mobile heat engines called thunderstorms.

Thunderstorms are dual-fuel heat engines. They run on low-density air, air that rises, condenses out the moisture and rewarms the air, which rises deep into the troposphere.

Figure 4. Afternoon thunderstorm circulation over the tropical ocean.

There are a couple of ways to get low density air. One is to heat the air. This is how a thunderstorm gets started, as a strong cumulus cloud. The sun plus GHG radiation combine to heat the surface, warming the air. The low density air rises. When that gets strong enough, a thunderstorm starts to form.

Once the thunderstorm is started, the second fuel is added to the fire — water vapor. Counter-intuitively, the more water vapor there is in the air, the lighter it becomes. The thunderstorm generates strong winds around its base. Evaporation is proportional to wind speed, so this greatly increases the local evaporation.

This, of course, makes the air lighter, and makes the air rise faster, which makes the thunderstorm stronger, which in turn increases the wind speed around the thunderstorm base, which increases the evaporation even more … a thunderstorm is a regenerative system like a fire where part of the energy is used to run a bellows to make the fire burn even hotter.

This gives thunderstorms a unique ability that, as far as I know, is not represented in any of the climate models. It is capable of driving the surface temperature well below the temperature that was needed to get it going. It can run on into the evening, and at times well into the night, on its combination of thermal and evaporation energy sources.

Thunderstorms can be thought of as local leakages that transport heat rapidly from the surface to the upper atmosphere. They cool the surface in a host of ways, utilizing a combination of cold water, shade, wind, spray, evaporation, and cold air.

And just like the onset of the cumulus circulation, the onset of thunderstorms occurs earlier on days when it is warmer, and it occurs later (and sometimes not at all) on days that are cooler than usual.

So again, we see that there is no way to assign an average climate sensitivity. The warmer it gets, the less each additional watt per metre actually warms the surface.

Even what I describe above doesn’t exhaust the variety of self-organization to decrease incoming sunlight and move more energy aloft. If the day continues to warm, the thunderstorms self-assemble into long, long rows of thunderstorms called “squall lines” (not illustrated). Between these long lines of thunderstorms there are equally long areas of clear descending air. Instead of the regime of individual “doughnut-shaped” circulation around each thunderstorm and cumulus cloud, it has all been replaced by long cylinders of air which sink in the valleys between the serried rows of thunderstorms, and rise up through their centers. This increases the rate at which the energy can be moved from the surface and converted into work.

Like all of the regime shifts, the change from individual tropical thunderstorms to squall lines is temperature dependent and threshold based. It occurs at the warmest temperatures.

Finally, once all of the fireworks are over, first the cumulus and then the thunderstorms decay and dissipate. A final and again different regime ensues. The main feature of this regime is that during this time, the ocean radiates about the amount of the energy that it absorbed during all of the previously described regimes.

Figure 5. Conditions prevailing after the night-time dissipation of the daytime clouds.

During the nighttime, the surface is still receiving energy from the GHGs. This has the effect of delaying the onset of oceanic overturning, and of reducing the rate of cooling. However, because there are no clouds, the ocean can radiate to space more freely. In addition, the overturning of the ocean constantly brings new water to the surface, to radiate and to cool. This increases the heat transfer across the interface.

As with the previous thresholds, the timing of this final transition is temperature dependent. Once a critical threshold is passed, oceanic overturning kicks in. Stratification is replaced by circulation, bringing new water to radiate, cool, and sink. In this way, heat is removed, not just from the surface as during the day, but from the body of the upper layer of the ocean.

And as mentioned above, by dawn the combined effect of clear skies and oceanic overturning has lost all of the heat of the previous day, and the cycle starts over again.

So let me recap.

1. There are a series of temperature thresholds in the tropics, each of which when crossed initiates a completely new circulation regime. In order of increasing temperature, these are the thresholds for cumulus formation, thunderstorm formation, and squall line formation.

2. The time of crossing of each temperature threshold depends (on average) on whether the local area is warmer or cooler than usual. As a result, the entire system is strongly homeostatic, tending to maintain the temperature within a certain range.

3. Feedback does not play any significant part in this temperature control system. Nor do small changes in the forcings. The system adjusts by means of the timing. The various regime change occur either earlier or later in the day (or not at all), to maintain the temperature.

4. In each of these separate regimes, the climate sensitivity  is quite different.

5. The climate sensitivity for the tropical ocean varies inversely with the temperature.

My conclusion from all of this is that the climate, like other flow systems far from equilibrium, contains homeostatic mechanisms. One effect of these mechanisms is that the tropical temperature is constrained to remain within a fairly narrow range.

And that’s why I describe myself as a climate heretic. I think the earth has a thermostat, one that is not represented in any of the current generation of climate models. I don’t think that climate is linear. I think that climate sensitivity is not a constant at all, but is a function of temperature. And to return to the title of the post, I think that the debate should not be about feedback at all, it should be a debate about the types and the effects of the various natural homeostatic mechanisms.

And all of those are definitely heresies to the latest IPCC Council of Nicean Climate …

My best to all,

w.