It is the exhortation of the politically correct media and left wing politicians that reducing carbon emissions will reduce the rate of average global warming. However, after much investigating I have found that this little polemic falls foul of a classic academic assumption that I detest. This is the "ceteris paribus" assumption, a Latin phrase that literally means "everything else being equal". The big black hole in the carbon myth is that everything else is not equal.
Before we delve further into the wonders of this inconvenient truth, I must declare that I am NOT a climate skeptic. The science behind the IPCC forecasts is solid, but what is not so solid is the economics behind it. The IPCC's emissions scenarios, which project future fossil fuel consumption are only made possible by the data of the International Energy Agency on reserves of these fuels. I hasten to add that countless environmentalists have poured scorn over the IEA's information, and with good reason- the IEA simply trusts declared reserves given to them by the various countries which they survey. These reserve figures are known to be a political artifact, fraudulently inflated to boost asset values (read: "investor confidence").
Now it might seem that this is irrelevant. If the IEA has exaggerated reserves, then we won't be able to emit the disastrous quantities of carbon that the IPCC's projected emissions scenarios rely on. On the other hand, if the IEA's reserves are correct, then climate change is still game on. However, things are not quite as simple as this.
The burning of fossil fuels contributes to concentrations of aerosol chemicals in the atmosphere, which have a short term cooling effect. Because they don't last long, the atmospheric concentration is highly responsive to changes in emissions. Carbon dioxide, on the other hand, has a long term heating effect, but unlike aerosol's, if you were to cease emissions, the atmospheric concentration would not rapidly plummet. The total radiative heating effect of all greenhouse gases is (2005) 2.45 W/M^2 (watts per meters squared) with a range of 2.18 to 2.7. However, this needs to be adjusted for the cooling effect of atmospheric aerosol, which gives us a figure of 1.41 W/M^2 with a range of 0.41 to 2.2. For the sake of transparency, I have calculated these from the parts per million concentrations of greenhouse gas equivalents and atmospheric aerosol's at http://www.skepticalscience.com/carbon-dioxide-equivalents.html (pro global warming site) and the IPCC's (pro global warming) formula of 5.35*log(new concentration/288)= radiative heating effect.
It is immediately apparent that drastic emission cuts would also lead to a collapse in the cooling effect of atmospheric aerosol's - to disastrous consequences- something that environmentalist James Lovelock lucidly explains in his book "The Vanishing Face of Gaia". Using the mid range figures, there would be a warming effect of 1.04 extra W/M^2, compared to today. The warming effect of the loss of atmospheric cooling aerosol's would ironically be greater than all the warming effect of greenhouse gas pollution in the last 35 years, except it would be much more sudden. It is proposed that carbon emissions are reduce by 80% on 1990 levels by 2050, although, for the sake of argument, let's say we were to eliminate them all within 10 years. The saving in terms of the prevented rise in carbon dioxide equivalents excluding aerosol would be in the order of 30 parts per million, yet the overall increase in total atmospheric forcing would be greater than the saving made by reducing greenhouse gas emissions.
According to data table 6.1 of the IPCC's most recent global warming study (2005 data), the total forcing of aerosols is -1.2, whereas the positive forcing of long lived greenhouse gases (Carbon Dioxide, Methane, Nitrous Oxide, and tropospheric Ozone) is 2.65. Halocarbons add an additional 0.34 W/M^2 but these have short term lifespans and are in any case being successfully and rapidly phases out so in the long term they are essentially an irrelevance. It is however misleading to give real figures, since what is really relevant is the change. For instance, the sun has an enormous forcing (over 1300) but the long term changes are very small. Around 1/2 of the forcing effect of the long lived greenhouse gases (LLGHGS) is of anthropogenic (man made) origin- there were lots of them there before we polluted the atmosphere with some extra. Overall, the positive forcing anthropogenic LLGHGS is balanced out by anthropogenic aerosols. The warming of the 21st century is attributable to the net difference between the two that only occurs due to short term minor greenhouse gases that are being phased out. We should, in other words, expect to see a reversal of the warming trend as the positive forcings decrease to match the level of negative forcings over the next few decades as the short term gases are phased out and disappear from the atmosphere. However, there is incessant political will to reduce LLGHG emissions, and thus stop the industrial processes associated with them that keep up the aerosol levels. The 21st century warming, of 0.8 deg C, attributable to the net forcing of 0.3-1 W/M^2 could be dwarfed if aerosol levels fell, leaving humanity, in Lovelock's words, to feel "the full force" (sic) of the anthropogenic greenhouse effect.
No matter how fast emissions cuts are carried out, the collapse of atmospheric aerosol concentrations is a long term inevitability. Interestingly, the IPCC does not give a forecast for these, even though it gives a forecast for all other radiative heating/cooling gases. Despite this being extremely mysterious, it only highlights the fact that a big jump in total CO2 equivalents from the figure including aerosol cooling to the figure excluding it. That would already put us on course for the 2 degree warming everyone is trying to avoid. Somebody has messed up big time with the plan to save the planet by reducing GHG emissions. It seems we really are stuck between a rock and a hard place.
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