The Physics of Global Warming is Complicated: A Note from Barry Moore
“Physics is rich in phenomena that are simple in appearance but cannot be calculated in simple terms. Global warming is like that. People may yearn for a short, clear way to predict how much warming we are likely to face. Alas, no such simple calculation exists. The actual temperature rise is an emergent property resulting from interactions among hundreds of factors. People who refuse to acknowledge that complexity should not be surprised when their demands for an easy calculation go unanswered.”
This is an admission that we are nowhere near a scientifically proven result with regard to the effect of CO2 on our climate.
In another article at RealClimate Gavin Schmidt suggests that all can in fact be explained in six easy steps.
Schmidt’s explanation is in conflict with Weart’s article and skips over some key points.
Following are the steps proposed by Schmidt, with my objections:
Step 1: There is a natural greenhouse effect.
Here Schmidt notes the average incoming IR (area of the disc divided by the surface area of the world = ¼) X 1366 = 341.5 W/m2 this is reduced to ~240 W/m2 by assuming an average albedo of 0.3 . Unfortunately this completely ignores reflection by clouds which covers approximately 65% of the globe.
The actual incoming radiation which is absorbed by the earth’s surface is, therefore, much less. Schmidt’s next assumption is the surface radiation by Stefan’s law (15 deg C avg.) is ~390 W/m2 and the TOA radiation is ~240 W/m2 thus he concludes ~150 W/m2 heats up our atmosphere. But, firstly we know that a fourth power law cannot be averaged and Stefan’s law is for black body radiators thus an emissivity factor must be assumed which reduces the 390 W/m2. Even more curiously it appears the entire heat balance consists of radiation.
Where are conduction, convection and evaporation factored in, these are just a few of the complexities that Weart was referring to.
Step 2: Trace gases contribute to the natural greenhouse effect.
Schmidt explains that with the latest technology (as of 1995) the spectrum from space can be analyzed line by line to detect the energy absorbed by CO2. However there is a qualifier, “For some parts of the spectrum, IR can be either absorbed by CO2 or by water vapour and so simply removing the CO2 gives only a minimum effect.”
Put another way, remove the CO2 and the water absorbs more energy, or take away the water and the CO2 absorbs more.
Step 3: The trace greenhouse gases have increased markedly due to human emissions.
This claim is based on extrapolating from ice core data which some claim underestimates past carbon dioxide levels by 30% to 50%. There is also the leaf stomata proxy work, Beck’s paper – 180 Years of Atmospheric CO2 Gas Analysis by Chemical Methods – and mass balance calculations based on the IPCC carbon cycle data none of which provide the necessary proof that the recent increase in carbon dioxide is unquestionably anthropogenic.
Step 4: Radiative forcing is a useful diagnostic and can easily be calculated.
I disagree and Spencer R. Weart would disagree. Here Schmidt trots out the only formula they have, RF = 5.35 ln(CO2/CO2_orig). So, if we use 385/280 for the CO2 increase we get RF= 1.7 W/m2 now at 0.75 deg C per 1 W/m2 we get an increase of 1.28 deg C.
However, if we look at the global temperature change since 1850 it is only 0.7 deg C. So something is wrong with the calculation as a measure of temperature increase based on radiative forcing from more carbon dioxide.
Step 5: Climate sensitivity is around 3ºC for a doubling of CO2. ( IPCC 4AR Pg.666)
Following on from my comments in step 4, this claim is an average based on data provided in the IPCC 4AR which provides a range of sensitivities generated from the IPCC formula and computer programs which attempt to evaluate the interaction of other factors such as water vapour.
Step 6: Radiative forcing multiplied by climate sensitivity is a significant number.
Schmidt explains “that current forcings (1.6 W/m2) x 0.75 ºC/(W/m2) imply 1.2 ºC that would occur at equilibrium. Because the oceans take time to warm up, we are not yet there (so far we have experienced 0.7ºC), and so the remaining 0.5 ºC is ‘in the pipeline’.”
This statement by Schmidt appears to be saying that the oceans absorb heat but do not experience a temperature change or the oceans absorb the heat but it takes time for the temperature change to affect the atmosphere.
The first concept is illogical, with regard to the second a convincing demonstration of the rapid reaction of global temperatures to ocean temperature changes was the effect of the super El Nino of 1998.
To illustrate the response of the globe and atmosphere to the sea surface temperatures the following graph shows anomalies for the global average (top) , the global sea surface (middle) and the global lower troposphere (bottom) temperatures from 1996 to 2008 showing the rapid response to the super El Nino of 1998.
No pipeline effect here.
Furthermore, where exactly is all the extra heat? The oceans cannot store heat “in the pipeline” without increasing in temperature which would create an immediate increase in atmospheric temperatures. Maybe it just does not exist in which case if we recalculate their formula the constant changes from 5.35 to 2.935. This is quite a change.
In conclusion, I agree with Weart, there are no easy answers and the IPCC case is far from proven. Attempting to explain climate changes by taking global averages and deriving empirical formulae is an extreme oversimplification of a very complex subject and is not valid proof.
Barry Moore P. Eng.