Thanks to Modtran, an online program maintained by the University of Chicago, we know that carbon dioxide’s heating effect is logarithmic. The first 20 ppm of carbon dioxide heats the atmosphere by 1.5°C. At the current concentration of 412 ppm each extra 100 ppm is only good for 0.1°C. Carbon dioxide is tuckered out as a greenhouse gas.
But what of methane which is the excuse du jour for wrecking livelihoods, towns, industries and whole economies? Methane, with a half life of nine years in the atmopshere, is carbon dioxide’s little brother in the pantheon of the satanic gasses.
Witness this headline about antics in New Zealand:
We return to Modtran to see what that oracle will tell us about methane’s heating effect. This is the model output converted to degrees C:
While not as pronounced as carbon dioxide’s drop off in heating effect with concentration, the effect is still there such that at the current concentration of 1.9 ppm, each extra 0.1 ppm heats the atmosphere by 0.05°C. With the methane concentration currently rising by 0.1 ppm every 20 years, the atmosphere will get an extra 0.2°C of heating by 2100. The reader can decide whether or not he/she/it need be worried by this projection.
But methane has only been going up at that rate for a few years. The atmospheric concentration of carbon dioxide has measured since 1958. Methane measurements only started in the mid-1980s and this is what the data looks like:
There is a steep rise at the beginning but then from the early 1990s to 2010 the concentration went sideways for nigh on 20 years. The Cape Grim concentration is particularly flat. NASA has helpfully provided a graph of rate-of-change:
There are three years – 2000, 2001 and 2004 – in which the methane level went down. Let’s disregard the noise and look at the bigger picture evident. And that is the rate of increase declined for 20 years and then went up for 20 years. A few more decades of observations might show whether or not this is cyclic.
But farms that have been going for generations might be wiped out by unnecessary concern about methane while we are waiting for that data. So we will make a stab at the underlying science. Two factors are likely involved.
Firstly plant productivity has been going up with the increase in the atmospheric carbon dioxide concentration. Parts of the West Australian desert now have 30% more plant matter than a scant 30 years ago. The same is true of the vast stretch of forest and tundra across northern Russia. Unless this vegetation is consumed by fire, its fate is to be the source of methane via termites or rotting. So the hand of Man is not necessarily involved in a rising methane level.
Secondly, the Sun was more active in the second half of the 20th century than it had been in the previous eleven thousand years. That stopped in 2006 with the end of the Modern Warm Period. The Sun has become less active as shown by this graph of solar extreme ultra violet produced by the University of Bremen:
Our current solar cycle, 25, is tracking lower than any of the previous four. The natural enemy of methane is ozone, the most reactive gas in nature. Ozone is produced in the upper atmosphere by radiation with wavelengths less than or equal to 242 nano metres acting on oxygen. So less ozone has been produced since 2006 and this is when the atmospheric methane level stopped falling and started rising again.
Case closed. Nothing to see here. Move along. Only idiots would get hung up on such a minuscule effect that we can’t change anyway. There are real problems coming at humanity that will take all our attention. Destroying the production base in the interim will only make our situation worse.
David Archibald is the author of The Anticancer Garden in Australia