Climatologist; I have a system of undetermined complexity and undetermined composition, floating and spinning in space. It has a few internal but steady state and minor energy sources. An external energy source radiates 1365 watts per meter squared at it on a constant basis. What will happen?
Physicist; The system will arrive at a steady state temperature which radiates heat to space that equals the total of the energy inputs. Complexity of the system being unknown, and the body spinning in space versus the radiated energy source, there will be cyclic variations in temperature, but the long term average will not change.
Climatologist; Well what if I change the composition of the system?
Physicist; see above.
Climatologist; Perhaps you don’t understand my question. The system has an unknown quantity of CO2 in the atmosphere that absorbs energy in the same spectrum as the system is radiating. There are also quantities of carbon and oxygen that are combining to create more CO2 which absorbs more energy. Would this not raise the temperature of the system?
Physicist; There would be a temporary fluctuation in temperature caused by changes in how energy flows through the system, but for the long term average… see above.
Climatologist; But the CO2 would cause a small rise in temperature, which even if it was temporary would cause a huge rise in water vapour which would absorb even more of the energy being radiated by the system. This would have to raise the temperature of the
Physicist; There would be a temporary fluctuation in the temperature caused by changes in how energy flows through the system, but for the long term average… see above.
Climatologist; That can’t be true. I’ve been measuring temperature at thousands of points in the system and the average is rising.
Physicist; The temperature rise you observe can be due to one of two factors. It may be due to a cyclic variation that has not completed, or it could be due to the changes you alluded to earlier resulting in a redistribution of energy in the system that affects the measurement points more than the system as a whole. Unless the energy inputs have changed, the long term temperature average would be… see above.
Climatologist; AHA! All that burning of fossil fuel is releasing energy that was stored millions of years ago, you cannot deny that this would increase temperature.
Physicist; Is it more than 0.01% of what the energy source shining on the planet is?
Climatologist; Uhm… no.
Physicist; Rounding error. For the long term temperature of the planet…see above.
Climatologist;Methane! Methane absorbs even more than CO2!
Physicist; see above.
Climatologist; Clouds! Clouds would retain more energy!
Physicist; see above.
Climatologist; Ice! If a fluctuation in temperature melted all the ice less energy would be reflected into space and would instead be absorbed into the system, raising the temperature. Ha!
Physicist; The ice you are pointing at is mostly at the poles where the inclination of the radiant energy source is so sharp that there isn’t much energy to absorb anyway. But what little there is would certainly go into the surface the ice used to cover, raising its temperature. That would reduce the temperature differential between equator and poles which would slow down convection processes that move energy from hot places to cold places. The result would be increased radiance from the planet that would exceed energy input until the planet cooled down enough to start forming ice again. As I said before, the change to the system that you propose could well result in redistribution of energy flows, and in short term temperature fluctuations, but as for the long term average temperature…. see above.
Climatologist; Blasphemer! Unbeliever! The temperature HAS to rise! I have reports! I have measurements! I have computer simulations! I have committees! United Nations committees! Grant money! Billions and billions and billions! I CAN’T be wrong, I will never explain it! Billions! and the carbon trading! Trillions in carbon trading!
Physicist; (gasp!) How much grant money?
Climatologist; Billions… Want some?
Climatologist; Hi. I used to be a physicist. When I started to understand the danger the world was in though, I decided to do the right thing and become a climatologist. Let me explain the greenhouse effect to you…
Dialogue posted in a comment yesterday over at The Telegraph by aelfrith.