## 7. Convection: the cooling feed back of CO2

After building my simulation and energy balance program, I was quite satisfied that they seemed to describe climate accurately, and showed all relations between the parameters, so I could experiment with them.
Just one question was left to answer: how can we quantify the feedbacks that are active in climate, i.c. those of temperature and CO2 concentration. If these feed backs were quantified, the model would be able to tell a lot more about the climate sensitivity of CO2.

So I tried to understand the drivers of the energy flows in the atmosphere.

The most important one is convection: not only is it the cause of wind, it also determines the height of the tropopause, and the temperatures in the atmosphere through the adiabatic laps rate.
But most of all: it drives latent heat transport, and even amplifies it because of the increased evaporation as a result of wind.

Convection is by far the greatest contributor to the Eu, and thus responsible for most of the cooling of the earth.

So convection is the great driver of climate.
Which leads to the next question:

What powers atmospheric convection?
In chapter 6, in the analogy of the oceans, we already established that you need both a low heat source and a high heat sink as drivers for convection:

1. Convection in a fluid or gas can only occur when there is a heat sink that is positioned above a heat source
2. The convection is restricted to the area between those two points

The atmospheric low heat source is obvious: we have a warm earth surface in the tropics.

Many consider the polar regions as the heat sink, but we already know that that doesn’t work: if that is the only heat sink, the atmosphere would fill up with hot air, actually (in potential temperature) as hot as the tropics at the hottest day of the year, and convection would come to an end. Obviously, no air can rise, when the air above it is warmer.

Without a high positioned heat sink, the only heat that flows upwards is by heat conduction. This is extremely low for air, thousands of times less than what we need for a convection that is comparable whith the present.

So we need a high positioned heat sink.
In fact, due to the second law of convection, we need one in the tropopause, since we know that there are convective air currents until that height.

It is no surprise that this heat sink is the result of the radiative properties of greenhouse gases (GHG). They radiate the energy into space that is transported upwards by convection.
This leads to a conclusion that is very hard to believe for many climate scientists: without greenhouse gases, convection would eventually stop completely.

I have discussed this with many climate scientists already, and even though they did not give me compelling arguments against it, most of them intuïtively refused to accept this.

They were right that accepting this conclusion should not be done lightly: it has far reaching consequences!

Cooling feed back of CO2
If there is no convection without GHG, there is a little convection with a little GHG added to the atmosphere.
And there would be a lot of convection with a lot of GHG in it.
By simple logic, convection, with it’s immensely cooling properties, has to be depending on GHG concentration.
This makes the greenhouse gases the key driver of convection!

Properties of a greenhouse gas concentration increase
So, independent of the temperature increase as a result of the warming properties of CO2, which causes a negative feed back through increased evaporation, there is already a cooling effect just by the mere increase in CO2 concentration.

The physical principle behind this, is the fact that more greenhouse gases create a larger temperature difference between the surface that is warmed by insolation, and the top of the atmosphere that is cooled by the emission of LWIR energy to space by the greenhouse gases.

This means that an increase of the greenhouse gas concentration has two simultanious and independent effects:

– it increases surface temperature by increased back radiation, though probably only with 0,4K, as shown in chapter 5, not even counting the negative feedback of increased evaporation by the higher temperature.

– it increases convection by increasing the temperature difference between the earth surface and the tropopause, which has a cooling effect

It should be noted that this cooling effect of increased convection is not a negative feedback on temperature rise, but a mere effect of the GHG concentration. It is not decreasing the warming, but providing an independent cooling effect.
This means that increasing GHG concentrations have a net cooling effect, if this cooling is larger than the warming, resulting from back radiation minus the increased cooling by evaporation it causes.

Conclusions on climate sensitivity
If only the back radiation of the LWIR from the surface emissions would be considered, we could conclude that climate sensitivity is almost certainly very close to zero, at the least considerably less than 0,4K, and may even be negative (resulting in cooling).

But the remarkable results of chapter 5 show that direct back radiation of the LWIR emitted by the surface may be almost neglectable, compared to the effects of the GHG concentration on incoming IR from the sun, and mostly compared to the downwards radiation of latent energy emerging from condensation in the lower and mid troposphere. This effect was (alas with very, very low accuracy) calculated to be up to 6K warming.
But chapter 5 also determined that this 6 K warming only required 5% increase in latent heat transport to be completely annihilated.

Since both the CO2 concentration increase and – independently – the warming resulting from it, cause an increase in convection, it is not improbable that this wil result in the required increase in latent heat occuring partially or completely, drastically decreasing the resulting climate sensitivity.

The accuracy of the calculation of the downward radiation of the latent heat emerging in the lower and mid tropopause can easily be substantially improved by meteorologists. At the moment my assumptions on the altitude where the condensation takes place are almost arbitrary. This improvement can result in a quite accurate calculation of the net climate sensitivity.

I didn’t – yet – find a way to accurately calculate the cooling effect of increased convection by higher GHG concentrations. This will be the next step on my way to provide an accurate physics-based estimation of an all-in climate sensitivity.

Conclusion of chapters one to seven
Of course all data and assumptions that I used to build both the radiation simulation and the energy balance sheet have to be improved, before the outcome can be accurate. And even then there are still basic unknowns that just have to be implemented manually, like the changes in cloud cover and transparency, and the influence of aerosoles.

But since everybody can work with the program, and it is so simple, it is possible to explore all options with thousands of “runs”, which would give a lot of good information, and would certainly clarify the sensitivity for all manually applied influences a lot.
It could turn out that they are not crucial, or that they can be implemented with enough accuracy to enable a reliable outcome.

By |May 9th, 2012|Climate|1 Comment

### One Comment

1. Theo July 13, 2015 at 1:51 am - Reply

This chapter has been considerably revised and extended.