CARBON DIOXIDE
A RECENT letter writer asked for a clear explanation of the role of carbon dioxide. Here it is.
Carbon is a precious commodity. A plant must sieve a roomful of air to capture a very few grams of it, using some for its structure and endowing the rest with energy captured from the sun.
But a “grazer” will soon steal that carbon for its own use. Predators then fight tooth and claw to get their share. Its energy used, the carbon is released back into the atmosphere to cycle again. It is the lifeblood of earth. It was once abundant, but much has been locked away over millions of years. Now it is being released again to invigorate the biosphere. Experiments have shown that plant growth rises dramatically when atmospheric carbon dioxide is increases, something that is vital to feed the world’s growing population.
Much has been made of its effect on temperature. Strictly speaking, carbon dioxide is not a greenhouse gas. The greenhouse effect is described as the reflection of long-wave warmth back to the surface by a high-altitude layer. Carbon dioxide does not work that way. It reflects nothing and does not form a layer. Instead it “colours” the atmosphere to block a very narrow range of wavelengths around 15 microns.
In consequence, radiation in that band cannot escape from the warm surface but must set out from the cold top of the atmosphere. A web search “Earth radiation spectrum” will clearly show satCo2 ellite images, with a “notch” around that wavelength and other notches caused by other gases, especially ozone.
As carbon dioxide increases, the notch gets slightly wider, meaning that global temperature increases to compensate. However the IPCC itself agrees that doubling the content will produce “radiative forcing” equivalent to a rise of less than a degree, while it would have to be doubled again to increase that rise to 1.6 degrees.
This is very different from the apocalyptic predictions of a couple of decades ago. In fact global temperatures have fallen for the last three years in succession, though this is unlikely to continue.
Some countries will be disadvantaged by a rise even as small as this, but most of the world’s population might welcome it. With temperatures changing at a rate of around one degree per century, animal and plant populations have plenty of time to adapt by moving a degree or so away from the equator while other species move in to take their place.
There is an almost religious belief that limiting atmospheric carbon dioxide is a worthy aim that should shape our lives and our economy. Can it really stand up to objective scrutiny?
JOHN BILLINGSLEY, Toowoomba