Guest Post by Willis Eschenbach

I got to messing about with the MODTRAN Infrared Light In The Atmosphere model. From the Help file.

Figure 1. Description of the MODTRAN model.

I was interested in the model because I wanted to see the difference between how much energy escapes from the surface to outer space at the equatorial regions versus the polar regions. So in my usual demented style, I wrote a program that downloads the results of a MODTRAN run so I can analyze them.

What I found was that in clear-sky conditions, subarctic summer, about 70% of the upwelling surface radiation makes it to space. And in clear-sky conditions, subarctic winter, about 81% makes it out. Finally, in the tropics, clear-sky, only about 65% of the upwelling surface radiation makes it to space.

This occurs for a couple of reasons. First, at cold temperatures, more of the energy is in frequencies less absorbed by CO2. And second, the poles are much drier than the tropics, and water is the major greenhouse gas.

Figure 2. Water content by latitude.

Having seen the MODTRAN results, I took a look to see how the MODTRAN numbers agree with the CERES data. Here’s the CERES view of how much of the clear-sky upwelling surface radiation makes it to space.

Figure 3. Global view, percentage of the upwelling radiation going to space. Clear skies only.

This shows the tropics as losing 63.7% of the upwelling longwave surface radiation to space. MODTRAN said 65% … close enough.

For the summer and winter subarctic, the subarctic is generally taken as the area from 50°-70° north latitude. To examine this, I took the summer and winter upwelling longwave percentages by latitude. Figure 4 shows that graph.

Figure 4. Percentage to space of CERES upwelling surface longwave (LW) by latitude and season, and MODTRAN summer and winter Sub Arctic LW percentage to space. Clear skies only.

Again there is excellent agreement between MODTRAN and CERES. And as you can see, there is a large difference in the amount of escaping LW in the tropics and towards the poles. Values are higher at the South Pole because the South Polar Plateau is quite elevated and extremely dry, and thus is above most of the greenhouse gases.

So why is all this important? That brings us back to the title of this post, “Advection”. As opposed to convection, which is a movement of energy in a vertical direction, advection is the horizontal movement of energy. And it is a huge movement. Here’s where the energy is moving from and to—it’s going from the tropics to the poles.

Figure 5. CERES average advection. Positive areas are advecting energy to the negative areas.

And this is important because the energy is moving from the location where less of it escapes to space, to the locations where more of it escapes to space.

Next, I took a look at the change in the total amount of energy advected over time. Figure 6 shows that result.

Figure 6. Increase in the total flow of energy advected (petawatts)

So … how much extra energy escapes to space from this increase in advection from the equator to the polar regions? To calculate that, we take the increase in petawatts, multiply it by the average increase in longwave escape in the polar regions over the escape in the tropics, and divide it by the surface area of the earth … which gives a result of an increase in top-of-atmosphere upwelling longwave radiation of 0.6 watts per square meter (W/m²).

And how does this increase in escaping longwave compare to other energy flows? Well, any increase in CO2 causes a corresponding decrease in longwave escaping at the top of the atmosphere. How much of a decrease? Assuming that the IPCC is correct in its estimate that a doubling of CO2 reduces top-of-atmosphere longwave by 3.7 watts per square meter (W/m²), the change over the 2000-2021 period shown above is … wait for it … a decrease of 0.6 W/m².

So over this period at least, the reduction of 0.6 W/m² in top-of-atmosphere upwelling longwave due to CO2 is exactly counterbalanced by the increase of 0.6 W/m² in top-of-atmosphere upwelling longwave due to increased advection.

Is this coincidental? It’s quite possible that it is. But if so, it’s an interesting coincidence …

And whether it is a coincidence or not, it goes to show that the standard CO2 theory of surface heating is oversimplified.

That theory says that if CO2 cuts down the amount of upwelling longwave headed out to space, the surface temperature perforce must increase to restore the top of atmosphere balance between incoming and outgoing radiation. Or to be more specific, the theory says that:

    • The amount of atmospheric CO2 is increasing.

    • This absorbs more upwelling longwave radiation, which leads to unbalanced radiation at the top of the atmosphere (TOA). This is the TOA balance between incoming sunlight (after some is reflected back to space) and outgoing longwave radiation from the surface and the atmosphere.

    • In order to restore the balance so that incoming radiation equals outbound radiation, the surface perforce must, has to, is required to warm up until there’s enough additional upwelling longwave to restore the balance.

But this analysis shows that, as I discussed in my post “Unbalanced At The Top“, there are more ways to restore the balance than a surface temperature increase … and thus, the usual CO2 theory is falsified.

---

My best New Year wishes to all,

w.

PS—For those interested, the other ways of re-establishing the TOA balance include:

    • Increased cloud or surface reflections can reduce the amount of incoming sunlight.

    • Increased absorption of sunlight by the atmospheric aerosols and clouds can lead to greater upwelling longwave.

    • Increases in the number or duration of thunderstorms move additional surface heat into the troposphere, moving it above some of the greenhouse gases, and leading to increased upwelling longwave.

    • A change in the fraction of atmospheric radiation going upwards vs. downwards can lead to increased upwelling radiation.

MY USUAL—I choose my own words carefully, and I am happy to defend them. However, I cannot defend your interpretation of my words. So, when you comment, please quote the exact words that you are discussing, so we can all be clear on your topic.

via Watts Up With That?

January 2, 2022

Advection