Watts Up With That? by Willis Eschenbach 9/23/2020
I ponder curious things. I got to thinking about available solar energy. That’s the amount of solar energy that remains after reflection losses.
Just under a third (~ 30%) of the incoming sunshine is reflected back into space by a combination of the clouds, the aerosols in the atmosphere, and the surface. What’s left is the solar energy that actually makes it in to warm up and power our entire planet. In this post, for shorthand I’ll call that the “available energyâ€, because … well, because that’s basically all of the energy we have available to run the entire circus.
Now, I don’t agree with the widely-held idea that the planetary temperature is a linear function of the “radiative forcing†or simply “forcingâ€, which is the amount of downwelling radiation headed to the surface from both the sun and from atmospheric CO2 and other greenhouse gases. Oh, the radiation itself is real … but it doesn’t set the surface temperature
My theory of how the climate operates is that the globe is kept from overheating by a variety of emergent phenomena. These phenomena emerge when some local temperature threshold is exceeded. Among the most powerful of these emergent phenomena are thunderstorms. In the tropics, thunderstorms emerge when the sea surface temperature (SST) is above about 27°C (80°F) or so. Here’s a movie I made of how the thunderstorms follow the sea surface temperature, month after month.
Figure 1. Tropical thunderstorms are characterized by tall cloud towers. The average altitude of the cloud tops is therefore a measure of the number and strength of the thunderstorms in the area. Colors show average cloud top altitude, with the red areas having the most and largest thunderstorms, and the blue areas almost none. The gray contour lines show sea surface temperatures (SSTs) of 27°, 28°, and 29°C, with the inner ring being the hottest.
Thunderstorms cool the surface in a variety of ways. They waste little energy in the process because they emerge to cool the surface only where it will do the most good—the hottest part of the system.
Among the ways thunderstorms cool the surface is via an increase in the local albedo. Albedo is the percentage of energy reflected back to space. The increase in this reflection (increasing albedo) occurs because the thunderstorm clouds both cover a larger area and are taller than the cumulus clouds that they replace. Their height and area provide more reflective surfaces to reject solar energy back to space.
In addition, the thunderstorm generated winds increase the local sea surface reflectivity by creating reflective white foam, spume, and spray over large areas of the ocean. And finally, a rough ocean with thunderstorm-generated waves reflects about two times what a calm ocean reflects (albedo ~ 8% rough vs ~ 4% smooth). That change in sea surface roughness alone equates to about 15 W/m2 less available energy.
Now generally, we’d expect that additional solar energy would be correlated with warmer temperatures. It’s logical that the relationship should go like this:
More available solar energy –> more energy absorbed by the surface –> higher temperatures.
We’d expect, therefore, that both the available energy and the temperature should be “positively correlatedâ€, meaning that they increase or decrease together. And in general, that’s true. Here’s the available solar energy, which is the sunshine that makes it past all of the reflective surfaces, the sunlight that is the one true source of all of the energy that heats, agitates, and powers the climate.
Figure 2. Available solar energy after all reflection from clouds, atmosphere, and the planet’s surface. The numbers are 24/7 averages.
As you can see, the poles are cold because they only get fifty watts per square metre (W/m2) or so from the sun. And the tropics get up to 360 watts per square metre (W/m2), so they are hot. The tropics are the main area where energy enters the system, and they’re also the hottest.
So far, what we see agrees with what we’d expect—available energy and temperature are correlated, going up and down together.
Now, my theory is that emergent phenomena act to constrain the maximum temperature. So an indication that my theory is valid would be if the amount of available solar energy were to not only stop increasing at high surface temperatures, but would actually go down with increasing temperature when the SST gets over about 27°C.
More:
https://wattsupwiththat.com/2020/09/23/watts-available/
