IAN Gray (Letters, April 3) was concerned about the influence of volcanoes on CO2 levels. Mt St Helens expelled some 10 million tonnes of CO2 over a nine-hour eruption in 1980. Mt Pinatubo emitted around 50m tonnes in 1991. This is less than the potential emissions of using the recently discovered Glengorm gas field, equivalent to 250m barrels of oil, some 75m tonnes of CO2 when burnt. Overall, humans added some 36 billion tonnes of CO2 to the atmosphere last year, roughly 100 times the annual volcanic activity. We can see the steady growth in CO2 levels in the Mauna Loa Observatory readings, from 320ppm to 410 over 50 years, but there are no dramatic spikes corresponding to volcanic activity.
Similarly Ian Cooper (Letters, April 2) inquired how the melting of the polar ice caps will cause sea levels to rise. As he is aware, the melting of the Arctic ice cap, floating on the Arctic Ocean, will simply re-place the same buoyant volume of ice with water. However, the ice caps over both Greenland and Antarctica sit on land, and as they melt, will add volume to the sea. Greenland is covered by enough water to increase sea levels by seven metres, and Antarctica by 60m. Conversely the ice caps of the last ice age, including a kilometre of ice over Scotland, contained enough water that sea levels were 120m lower. Additionally, as the sea heats up, it expands, contributing to roughly a third of the sea level rise so far.
And finally Geoff Moore (Letters, April 3) wrote that 2019 had more Arctic sea ice at winter maximum on March 13 than 2006 or 2007, so global warming is a myth. Unfortunately the NSIDC data for the start of April 2019 is a record low for the time of year, such are the problems of using data that is heavily dependent on the weather of the few days before the measurement. The NSIDC figures show a 2.7 per cent reduction in March Arctic sea ice extent per decade since satellite measurements began in 1979, losing an area of ice the size of Scotland every two years, or an icy Brexit every six years.
Alan Ritchie,
72 Waverley Street, Glasgow.
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