Last week I attended in UQAR a long presentation given by a climate modeler from the OURANOS consortium on regional climatology and adaptation to climate change, based in Montréal, Québec. I picked among the wealth of information provided a survival kit to use in any occasion you face a so-called skeptic. They are inconveniently widespread now, even among your family, friends or neighbors, the federal government, and worse, they are spreading outside of the US into Canada as I'm writing this blog entry...
So, skeptics cherish a
handful of "arguments", which are not (only) bad or misunderstood science, but
are essentially outdated science, and when you'll face it you'll have to debunk
it! The skillful skeptic will probably not deny the global increase in atmospheric
CO2 since the beginning of industrialization (Documented first by
Callendar in 1938), as Andy recently pointed out, but rather deny its impacts
on climate through a short list of arguments, some of them being:
"Climate changes are forced by the sun (not my SUV)"
This argument is incomplete and out of date. This was a legitimate scientific hypothesis formed by Milankovic in the 40's. He thought that the intricate interplay of the precession, obliquity and eccentricity of the earth altered the radiative forcing from the sun, and thus the climate. However as early as the 70's with the help of the first ice cores (some made by Milankovic himself...), it was proven that this effect would essentially modify the seasonality of the sun forcing, and not the total quantity of radiation reaching the earth which is what is important in the radiative balance of the planet. Moreover it could not explain a number of fast historical climate changes events, nor the warming trend of the last 30 years.
The more subtle skeptic will try to ensnare you in some apparently complex issues like:
"H2O vapor already blocks infrared wavelengths, so an increase in CO2 (by my SUV) won't change the earth's radiative balance"
This argument is of the
oversimplified type, and is actually wrong. To better get the importance of infrared absorption by gases, please refer
to this pages for a quick introduction of radiative balance of the planet and
greenhouse effect. Basically, H2O doesn't absorb at all the infrared
wavelengths that CO2 can absorb. So despite water vapor being
overwhelmingly abundant, there is still room for an increase in heat in the
atmosphere solely due to increased infrared absorption by increased atmospheric
CO2. Plass realized this in the early 50's after a careful study of
infrared wavelengths absorption by water vapor and other gases. He published as
early as 1956 all of the major figures now confirmed by measurements and advanced
numerical models in the most recent IPCC science reports: temperature increase
by year 2000, temperature increase if doubling of CO2, etc. Plus, as Andy has just shown, an increase in heat due to CO2 will lead to an increase in water vapor, ad hence a positive (more warming) feedback...
And about feedback and climate numerical models, what about:
"Models are oversimplified, don't take in to account water vapor (!) and overlook feedback."
Well nowadays climate models are FAR from simple, and beyond their physical and numerical structure, the way they are used presently (ensemble approach, with powerful statistical methods to get meaningful confidence interval etc.) are far more advanced than usually thought. There is a widespread misconception equating the problem of predicting weather (a chaotic monster) and climate (the statistical resultant of many weather events)...
For water vapor, it was first modeled in 1967 by Manabe & Wetherald, and there is simply NO modern model that overlook it. Finally, most climate models now incorporate feedback from land (including vegetation, wild fires, volcanoes etc.), the ocean and the cryosphere (ice).
I leave you with a very nice animation presenting the current state-of-the-art climate modeling. This animation was made for the Pierre-Simon Laplace Institute of France, so the comments are in French, but I can assure you it's a great piece of climate modeling for the layman!