Confusion on cause of global warming
IN his recent letter, Mike Baker expresses confusion about the causes of recent global warming. However, his thoughts concerning conflicting theories arise because he is misinformed about the history of climate change studies and because he doesn’t understand the different roles played by ozone and carbon dioxide in the Earth’s climate system.
To elaborate – there was very little comment from climate science on potential global cooling in the 1950s, when heavy snows affected Dartmoor. Certainly, there is a myth propagated by those who like to deny anthropogenic global warming (AGW) that there was a consensus among scientists in the 1970s that a new ice age was imminent.
When the published scientific literature for the 1970s is analysed, it is found that six times more papers were published about the dangers of global warming than those of global cooling. However, considerable prominence was given to the minority view by the media at the time. Since the 1970s, the evidence for AGW has been so overwhelming that no publishing climate scientist forecasts imminent cooling and the onset of ice advance.
Concerns about ozone depletion began in the late 1970s because of a steady lowering of the total amount of ozone in Earth’s atmosphere
(the ozone layer) and a much larger springtime decrease in stratospheric ozone around Earth’s polar regions (the ozone hole).
These declines were caused by manufactured chemicals, especially halocarbon refrigerants, solvents and propellants.
The ozone layer prevents the most harmful wavelengths of ultraviolet (UV) light from passing through the Earth’s atmosphere. It was the decline in this protection and resulting increases in skin cancer, sunburn, permanent blindness, and cataracts, and not any worries about global warming, that persuaded governments world-wide to adopt the Montreal Protocol in 1987, which bans the production of ozonedepleting chemicals and has led to the stabilization and partial recovery of the ozone layer.
The role of carbon dioxide in the atmosphere, as the principal non-condensing greenhouse gas, is to trap outgoing longwave radiation from the earth and to cause warming. It is therefore the rapid rise in atmospheric CO2 levels, due to increased emissions and the large-scale removal of vegetation sinks for this gas occurring as a result of human activity particularly since the industrial revolution, that unequivocally has been the primary driver of significant recent global warming.
Professor Bruce Webb Exeter, Devon