Solar Sensitivity

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Guest Post by Willis Eschenbach

In my previous post, “Global Scatterplots“, I discussed how a gridcell-by-gridcell scatterplot of the entire globe could be used to gain insights into the relationship between two variables. The variables I discussed in that post were the cloud radiative effect (CRE) as a function of the temperature. At the end of that post, I threatened as follows:

I will return to what I’ve learned from other gridcell scatterplots in the next post.

So as foretold in the ancient palimpsest texts … he’s baack!

For this expedition into global scatterplots, Figure 1 shows the surface temperature as a function of the amount of solar power that’s actually entering the climate system. This available solar power is the top-of-atmosphere (TOA) solar, minus the “albedo reflections”, which are the amount of sunlight reflected back to space by the clouds and the surface.

Figure 1. Scatterplot, gridcell-by-gridcell surface temperature versus available solar power. Number of gridcells = 64,800. The cyan/black line shows the LOWESS smooth of the data. The slope of the cyan/black line shows the change in temperature for each 1 W/m2 change in available solar. The data in all of this post is averages of the full 21 years of CERES data.

I’ve mentioned before how I love the surprises that science brings. The surprise for me in this was that there are three very distinct regimes shown in Figure 1.

The left side of the plot, below around 100 W/m2 available solar, shows the areas near the poles where there’s little available solar power. In those areas, the temperature rises very quickly with increasing solar power.

Then there’s a long basically straight-line section from ~ 100 W/m2 available solar up to around 300 W/m2.

And finally, from about 310 W/m2 to 360 W/m2, there is a flat straight line, with no slope at all.

That last was the biggest surprise to me. Once the average available solar power is above 310W/m2, you can add up to an additional 50 W/m2 without increasing the surface temperature one bit. And remember, these are not short-term changes. This reflects the effects of an additional 50 W/m2 applied over decades and centuries.

Hmmm … an increase of 3.7 W/m2 from a doubling of CO2 is supposed to cause a 3°C temperature rise. But here’s a part of the world where a change of 50 W/m2, more than ten times as large, does … nothing. However, I digress …

How large a part of the world shows this insensitivity? Figure 2 outlines the areas below 100 W/m2, where there is a steep rise of temperature with increasing solar, and the areas above 310 W/m2, where there is NO rise of temperature with increasing solar.

Figure 2. Available solar power (TOA solar minus albedo reflections), Pacific-centered and Greenwich-centered views. Areas in red outlined in cyan/black do not change temperature with increased average solar input. Polar areas in blue outlined in white/black show where the temperature is very sensitive to increased solar input. Dotted horizontal lines show the tropics and the arctic/antarctic circles.

Note that the red areas that are insensitive to increased solar input are all in the tropics and are virtually all oceans. They cover half of the tropical area or about 22% of the planet’s surface.

The blue areas of high temperature sensitivity to solar variations, on the other hand, only cover about 8% of the planet.

Returning to Figure 1, recall that I said that “The slope of the cyan/black line shows the change in temperature for each 1 W/m2 change in available solar.” Figure 3 shows exactly that, the slope of the cyan/black trend line in Figure 1.

Figure 3. Slope of the trend line in Figure 1. This shows the amount of change in the temperature for a 1 W/m2 change in available solar.

Here we see the same three regions that we can see in Figure 1. At the left, below ~ 100 W/m2 of available solar, the sensitivity of temperature to changes in solar input is quite high. (Remember that this is not the climate sensitivity to CO2 changes. It is the sensitivity to available solar.)

Then, from 100 W/m2 to 300 W/m2, the sensitivity is basically unchanged, averaging 0.16 °C per W/m2.

Finally, above ~ 310 W/m2 of available solar, the temperature is totally insensitive to changes in available solar power.

Note that this means that solar power has to rise by about six W/m2 to raise the temperature of 70% of the planet by 1°C … and remember that in half the tropical ocean, 22% of the planet, that same six W/m2 increase in available solar doesn’t do doodly-squat to the temperature. (“Doodly-squat”? That’s a technical scientific term for zero.)

Conclusion? Simple.

It takes ~ 5 W/m2 of additional solar input to raise the surface temperature by a single degree C.

Let me close with the threat from my previous post, viz:

I’ll leave this here, and I will return to what I’ve learned from other gridcell scatterplots in the next post.

Best regards to everyone on a foggy coastal day,


I IMPLORE YOU: When you comment, quote the exact words you are responding to. I can defend my own words. I can’t defend your rephrasing of my words. Thanks.

via Watts Up With That?

October 16, 2022