The following is a letter in response to “CO2 a tiny fraction of atmosphere”, Progress, Oct. 15.
Thanks to Francis Patrick Jordan for asking “How can a reasonable person argue that carbon dioxide is the primary driver of climate change?” The answer lies in wavelengths of energy and the structure of molecules.
Energy from the Sun reaches Earth in the range from ultraviolet to infrared, peaking in the visible range. This energy warms the Earth and Earth in turn radiates energy, as any object warmer than absolute zero does. Earth radiates in the infrared range.
The atmosphere, as Francis pointed out, is 77% nitrogen (N2) and 21% Oxygen (O2). N2 and O2 molecules can stretch, but only symmetrically. Molecules with three atoms like carbon dioxide (CO2), water vapour (H2O), nitrous oxide (N2O) or ozone (O3), or five atoms like methane (CH4), can stretch and bend asymmetrically at frequencies that match wavelengths of infrared energy, allowing absorption and re-emission. A graphic is available at http://tinyurl.com/yj3ljb7 to illustrate. Some of that energy will end up emitted back to Earth, adding to the total energy reaching the planet. That is the greenhouse effect.
Atmospheric CO2 concentrations fluctuate naturally, over the past million years up and down between about 180 ppm to about 280 ppm. Since the industrial revolution it has shot up to its current level of about 400 ppm due to burning of fossil fuels. A graphic at http://tinyurl.com/qeuwc2g illustrates. Current Canadian and British Columbian economic and energy policies ensure that our carbon emissions will accelerate. It is a grand experiment.