Tuesday, May 20, 2014

Climate, CO2 and cooling

A very interesting and detailed take on climate change is to be found in this fascinating post by E M Smith, aka blogger The Chiefio. Written back in December 2012, it is long and detailed but well worth reading. This brief post is merely my take on his ideas.

Firstly the role of CO2.

Most people interested in the climate change debate will know that CO2 in the stratosphere is thought to have a cooling effect as opposed to its supposed warming effect in the troposphere. The cooling effect of CO2 may also be causing the stratosphere itself to cool.

One key finding was the importance of the impact of CO2-induced temperature change on stratospheric ozone in estimating temperature trends. The decreased stratospheric temperatures due to a CO2 increase slowed stratospheric ozone destruction; the higher ozone concentrations caused heating that slightly offsets CO2-induced cooling.

Although simple physics suggests CO2 could act as a so-called greenhouse gas in the troposphere, it doesn’t tell us the magnitude of any resultant warming. A possible warming effect may be swamped by other processes – the physics doesn’t tell us. Many have tried to torture the data into telling them what they want to hear, but so far none have succeeded.

Yet many climate sceptics and all orthodox global warming proponents agree that increasing atmospheric CO2 should cause some detectable warming in the troposphere. Put simply, both groups think CO2 must slow down radiative surface cooling because of its capacity to absorb outgoing infrared radiation.

The crucial difference in views between the two sides is how much warming we should expect - the so-called climate sensitivity to CO2. Yet the current global temperature standstill shows both views to be wrong. Climate sensitivity to CO2 appears to be as near zero as makes no difference.

So instead of bodging the thing with ad hoc hypotheses why not assume that heat transfer in the troposphere is primarily driven by convection, evaporation and condensation? Hardly a radical assumption given our knowledge of weather. There are many other factors to consider such as clouds, El Niño, volcanic activity and ocean heat capacity, but to avoid an impenetrable fog of complexity we first have to stand back and look at broad possibilities.

Next the tropopause.

The tropopause lies between the troposphere and the stratosphere. Smith sees understanding the nature of the tropopause as a key to understanding how global heat transfer from the surface occurs in two distinct bands in two distinct ways.

The troposphere where heat transfer is primarily driven by convection and water vapour.
The stratosphere where heat transfer is primarily radiative.

Of particular interest is how the height of the tropopause is influenced by the amount of heat which has to be transported from troposphere to stratosphere. As a result, the tropopause is higher at the equator than it is at the poles.


Even if CO2 does warm the troposphere by an amount we can’t yet measure, the heat may be transferred upwards via convection, condensation and evaporation - not radiation.

Stratospheric cooling rates: The picture shows how water, cabon dioxide and ozone contribute to longwave cooling in the stratosphere. Colours from blue through red, yellow and to green show increasing cooling, grey areas show warming of the stratosphere. The tropopause is shown as dotted line (the troposphere below and the stratosphere above). For CO2 it is obvious that there is no cooling in the troposphere, but a strong cooling effect in the stratosphere. Ozone, on the other hand, cools the upper stratosphere but warms the lower stratosphere. Figure from: Clough and Iacono, JGR, 1995; adapted from the SPARC Website. 

Note the above picture of stratospheric cooling rates. The red bit in the bottom left below the tropopause (dotted line)  is heat being dumped into the stratosphere by water vapour. The narrow pale blue band to the right of that and also below the tropopause – that’s CO2 doing nothing much.

Above the troposphere, convective heat transport ends, radiative processes take over and CO2 plus ozone are kept busy radiating excess heat into space. Those are the two colourful elongated oval shapes.

I’m not suggesting Smith's overall schema is what actually happens because nobody has that sorted, but I like his style. Climate conjectures are all vulnerable in one way or another, because that's the nature of the beast, but even in outline these ideas feel coherent to me. They do not seem to violate any scientific laws and fit well with observation.


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