Sir – Although Professor Graham Lee, having set off for the Arctic, may be uninterested in replies to his prominent letter (March 27), your readers may well be. When asserting the effect of volcanoes on the earth, he confusingly includes CO2 in his list and accuses others of naivety.
The US Geological Survey estimates that per annum, human-caused CO2 emissions at the present time are 80 times those from all land-based volcanoes, assuming a high estimate for the latter. The British Geological Survey comes to a similar conclusion.
Surprisingly the occasional massive eruption such as 1991 in the Philippines, which produced more CO2 than Mt St Helen’s in 1980, makes little difference to this general conclusion. The graph of CO2 in the atmosphere shows little sign of wavering after 1991. I am inclined to believe the USGS and BGS. Other gases and also ash do have a large effect and SO2 from volcanoes cools the planet for a year or two until the effect of CO2 reasserts its dominance.
The recent report from IPCC shows that the debate needs to be about acceptable ways of reducing CO2 emissions and how to reduce the effect of what has already been committed.
Julian Gallop, East Hagbourne
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