By Phil Harris, Cassandra's legacy
Recently Ugo Bardi raised the matter of methane and the fact that compared with geological history, the present level in the atmosphere of this potent "greenhouse-gas" is exceptionally high. We see methane bubbling from the arctic margins. We know the present level is around 1800 parts per billion (1.8ppm); more than 2.5-fold the pre-industrial level. We know this rise has been sudden and that most of it occurred in the 20thC up to about year 1990, and that interestingly for a rapidly oxidised molecule, this high level has been sustained, and lately has begun to increase again. After a brief discussion with Ugo, I decided to attempt an update of my own knowledge.