Global warming and CFCs

The following e-mail was received in response to a report dated June 4 in the CCE E-Newsletter entitled: “New theory finds air-conditioner chemicals cause global warming: University of Waterloo professor publishes article saying CFCs not CO2 are the problem.”

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With respect to professor Lu’s article on blaming CFC’s on global warming, I’m disappointed when I see such a paper get so much press. Andrew Weaver, Canada’s top climate scientist from the University of Victoria, has called it “ridiculous.”

It is fairly well known that CFCs are being eliminated due to their ozone depletion potential and are being replaced in most instances, such as in chillers and automobile air conditioning systems, by HFCs, such as HFC134a. HFCs have no ozone-warming potential but their global warming potential (GWP) is about equal to that of CFCs. In other words, changing from CFCs to HFCs is not reducing our man-made greenhouse gasses that are warming our atmosphere. (Global warming potential was not considered in the Montreal Protocol.)

There are a lot of things scientists are working hard to understand, but greenhouse gases were discovered back in 1824 by Joseph Fourier and have been studied ever since. After 189 years, there’s not much we don’t know about them. We know that carbon dioxide represents about 80% of our non-condensing GHGs (NASA) and is therefore the gas we are most concerned about.

We know it takes a molecule with a minimum of three atoms to form a GHG, as the positive and negative forces must be able to work against each other in order to heat up. This is not possible if there are only two atoms. Nitrogen and oxygen, making up about 99% of our atmosphere, are therefore not greenhouse gasses. Carbon dioxide, methane, and nitrous oxide, are our three most common GHGs, but man-made GHG’s such as CFC’s, HFC’s, SF6, NF3 etc. are not insignificant. We have now increased our carbon dioxide to about 400 ppm, but if we include all our non-condensing greenhouse gasses and express them as an equivalent carbon dioxide, CO2e, the number according to Dr. Prinn at MIT, is CO2e = 478 ppm.

To understand the modern effect of our other GHGs, consider that back in the mid-Pliocene, about 3 million years ago, the CO2 level was about 380 ppm. The best guess of scientists is that CO2e at that time for 380 ppm, would be about 400 ppm. Note that this is a representative figure, close to our present level of carbon dioxide, but up to 425 ppm for CO2 has been published for that time period.

As you go back in time, the picture gets fuzzy. We do know that the temperature back then was about 2.5 – 3 degrees above our pre-industrial value and sea levels were 15 – 20 metres higher than today. These could be seen as the minimum stabilization levels at our present GHG levels, which unfortunately are still increasing every year.

The known values of CO2 and resulting temperature of the mid-Pliocene period indicates that the Intergovernmental Panel on Climate Change (IPCC) figure of 2 degrees at a carbon dioxide level of 450 ppm as being our highest safe level is political and not based on what scientists know. Two degrees is higher than the earth has seen in millions of years and will result in a sea level rise of tens of metres. As such, the figure is seen by many as being a political statement to try and save the Copenhagen Accord. Unfortunately, however, the statement has been bought by many people despite well known scientists such as James Hansen and Myles Allen showing that 450 ppm is well above the maximum safe level and is not equal to a stabilization temperature of 2 degrees. (The IPCC used Charney’s constant for earth’s sensitivity to CO2 and that doesn’t account for positive feedbacks of things like the melting polar ice sheets.)

James Hansen’s work has indicated that a CO2 equal to 350 ppm is our highest safe level and that we may have to reduce this to 325 ppm in order to regain our Arctic ice. This knowledge started Bill McKibben’s 350.org movement and let Myles Allen to work out that 350 ppm actually gives us a stabilized temperature approaching 2 degrees. Unfortunately, getting back to 350, where we were in 1987, will be very difficult.

Lee Norton, P.Eng.

St. Catharines, Ontario.

Lee Norton is an editorial advisor to Canadian Consulting Engineer magazine.

To see the original article that he is referring to in Canadian Consulting Engineer’s E-Newsletter, click here.