Guest Post by Willis Eschenbach
At the end of my last post , I said that the climate seems to be an inherently stable system. The graphic below shows ~2,000 climate simulations run by climateprediction.net. Unlike the other modelers, whose failures end up on the cutting room floor, they’ve shown all of the runs … including the runs that ran right off of the rails.
Figure 1. Climate simulation runs from climateprediction,net.
Notice that many of the runs go badly wrong, either cooking the planet at some 8°C (14°F) hotter than at present, or spiraling down into an ice-covered unreality. To me this is a perfect example of the basic misunderstanding of how the climate works. People think that the global temperature is free to take up any temperature at all, and that if the forcing changes, the temperature must change. But it is not free to go off of the rails. Instead, the global temperature is an inherently stable system.
Now, what does it require for a natural heat engine like the global climate to be inherently stable? The general way that humans control heat engines like say an automobile engine is by controlling the “throttle”, which in an automobile is what the gas pedal connects to. The throttle decrease or increases the amount of fuel that is entering the engine. To be stable, you need some system that opens or closes the throttle based on some criterion.
In the climate system, of course, the throttle is the variable albedo of the earth. The “albedo” of an object is a number from 0.0 to 1.0 that measures the fraction of solar radiation that is reflected from the surface of the object. It’s usually given as a fraction, although I prefer it as a percentage (0% to 100%). The albedo of the earth is about 0.29, meaning 29% of the sunlight is reflected back to space.
As I showed in my last post, the albedo generally decreases with temperature … up to around 26°C or so. Above that the albedo rises rapidly. As a result, in much of the tropics when the ocean warms the albedo increases, rapidly cutting back on the incoming solar energy.
In such a system, when the earth is cooler than the equilibrium temperature, the solar input goes up, increasing the temperature. And conversely, when the earth is warmer than the equilibrium temperature, the solar input goes down, and the earth cools back to the equilibrium temperature.
In the comments to my last post, someone asked how the increase in albedo worked out on a daily basis. To answer that, I need to take a bit of a diversion.
I got interested in climate in the late nineties. Most folks I read wanted to understand why the earth’s temperature had changed over the 20th century. I had a very different question—I wanted to know why the earth’s temperature had changed so little over the 20th century (a variation of ± 0.3°C). Since the earth’s temperature is about 290 Kelvin, that’s a variation of plus or minus a tenth of a percent or so. As someone who has dealt with regulated engines, to me that was astounding long-term stability. Over the 20th century we had droughts, the clouds came and went, we had volcanoes, times of lots of hurricanes, times of few hurricanes … and the temperature went nowhere. Plus or minus a tenth of a percent.
At the time I started tackling the problem of climate stability, I was living in Fiji. At first, I spent a whole lot of time searching for the reason that there was such long-term stability. I tried to identify and understand any processes acting on multi-decadal time scales. I thought about the ebb and flow of CO2, about how the CO2 makes the rain acidic and dissolves the mountains over millennia. I thought about the purported barycentric solar cycles. I thought about the multidecadal oscillations.
No joy.
In the evenings after work I’d walk and think, think and walk. I picked up and discarded dozens of possibilities. I can’t tell you how far I walked thinking about long-term, slow compensatory systems that could keep the earth on track for a century and more.
Then one day I had a curious thought. I thought, if there were a system that kept each day within a certain temperature range, it would keep that week within that same temperature range, and it would keep that year within that temperature range, and that decade, and century, and millennium … like a fool, I’d been looking at entirely the wrong end of the time spectrum. I needed to look at minutes and hours, not decades and centuries.
This changed the entire direction of my research overnight. I started looking for processes that would regulate the temperatures on a daily basis … and since I was living in Fiji, I didn’t have far to look. I started to think that the action of the tropical cumulus clouds and in particular the thunderstorms were the real actors in the climate pageant.
I could see the daily tropical cycle unfolding most days. Clear at dawn. Then cumulus clouds form usually before noon. Thunderstorms in the afternoon, sometimes lasting into evening or night. However, I was still at a great disadvantage. I didn’t understand how the control worked. The problem was that even in the tropics you have seasons, and not every day is the same. Plus there’s day and night, it was all so complex I couldn’t see how the control was effected. I wanted some point of view where I didn’t have to deal with all of that day/night, seasons stuff.
Then one day I realized that there was a point of view which freed me from all of those problems. This was the point of view of the sun. You see, from the sun’s point of view it’s always daytime—from the sun’s point of view, there is no night. And there are no seasons—underneath the sun, it’s always eternal summer.
So to investigate the cumulus and the thunderstorms from the sun’s point of view, I used the satellite local-noon-time images from the GOES-West weather satellite. I averaged the photos over an entire year, to show the average cloudiness of the Pacific. Figure 2 shows that result:
Figure 2. Average of one year of GOES-West weather satellite images taken at satellite local noon. The Intertropical Convergence Zone is the bright band in the yellow rectangle. Local time on earth is shown by black lines on the image. Time values are shown at the bottom of the attached graph. Red line on graph is solar forcing anomaly (in watts per square meter) in the area outlined in yellow. Black line is albedo value in the area outlined in yellow.
Looking from the point of view of the sun does a very curious thing—it trades time coordinates for space coordinates. For example, in the photo above, it is always local noon at the point directly under the sun. Noon is not a time. It is the vertical line running up the middle of the picture. Sunrise is always at the left edge of the view from the sun, and the left half of the picture is the time before noon. Sunset is always at the right edge of the view from the sun, and afternoon is the right half of the picture. We’ve put spatial coordinates in place of temporal coordinates.
From this, you can see that the onset of cumulus clouds is at about 10:30. This is shown by the increase in albedo (black line at picture bottom). By 11:30 there is a fully developed cumulus field. This shift in albedo changes the reflected sunlight by about 60 W/m2. And that field of clouds persists all through the afternoon (right side of the picture above).
And most important, from the sun’s point of view I could finally understand how the albedo control is actually effected—via variations in the timing of the onset of the cumulus and thunderstorm regimes. What happens is that if the Pacific is warmer than usual, the cumulus clouds and thunderstorms shift to the left in the image above by emerging earlier in the day. This, of course, reflects more of the sunlight. And if the Pacific is cooler than usual, the clouds and thunderstorms shift to the right, emerging later in the day or not at all, and thus exposing more of the area to the stronger sunlight of the mornings. The clouds act like a reflective window screen that covers more or less of the day, depending on the temperature.
Now, from this hypothesis we can advance some testable predictions. First, albedo should be positively correlated with temperature in the tropical Pacific. This is confirmed by my previous post. Next, we should be able to detect the effect of the variations in cloud onset on the daily temperature record … which hopefully will be the subject of my next post.
Finally, while the cumulus and the thunderstorms control the throttle by regulating the amount of energy entering the system, there are a variety of other temperature regulating phenomena as well. What all of these have in common is that they are “emergent” phenomena. These are phenomena that emerge spontaneously, but only when conditions are right. In the climate system, these phenomena typically emerge only when a certain temperature threshold is surpassed.
In the tropical daytime system, once a certain temperature threshold is reached the cumulus clouds start to form. But often, the reduction in incoming sunlight is not enough to stop the daily warming. If the surface continues to warm, at some higher temperature threshold thunderstorms form. And if the surface warms even more and a third temperature threshold is surpassed, yet another phenomena will emerge—the thunderstorms will line up shoulder to shoulder in long serried rows, with canyons of clear descending air between them.
Thunderstorms are natural refrigeration cycle air-conditioning machines. They use the same familiar evaporation/condensation cycle used in your air conditioner. But they do something your air conditioner can’t do. They only form exactly when and where you need them. When there is a hot spot in the afternoon on a tropical ocean, a thunderstorm soon forms right above it and starts cooling the surface back down. Not only that, but the thunderstorm cools the surface down below the starting temperature. This can not only slow but actually reverse a warming trend.
And if there are two hot spots you get two thunderstorms, and so on … do you see why I argue against the entire concept of “climate sensitivity”? When you add additional forcing to such a system, you don’t just get additional hot spots.
You also get additional thunderstorms working their marvels of refrigerational physics, so there is little surface temperature change.
It’s one AM, big moon a few days past full. Think I’ll go back outside, I heard a fox barking outside around moonrise. Best to all, moon over your shoulder, more to come,
w.
The Perennial Request: If you disagree with someone, please have the courtesy to quote the exact, precise words that you disagree with. That way we can all understand your objection.
Further Reading:
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