The Manua Loa weather station. Photo: flickr.com Flatbush Gardener cc by-nc-nd
The symbolic level of 400 ppm of carbon dioxide in the atmosphere has been exceeded at Mauna Loa in Hawaii for the first time since records began in 1958. It is the oldest of all the atmospheric measurement stations in the network of stations that the Global Atmosphere Watch coordinates. It was on 9 May this year that a reading of 400.3 ppm was recorded as the daily average. Levels exceeding 400 ppm have previously been recorded at several more northerly stations. The first was Barrow in Alaska, where the threshold was exceeded back in April 2012. The plus 400 ppm reading at Mauna Loa has since been followed by stations at locations closer to the equator, including the Canary Islands.
The highest concentrations of carbon dioxide over the year generally occur during the northern atmospheric spring, just before large amounts of carbon dioxide are absorbed by growing vegetation.
The global annual average concentration in 2011 was 390.9 ppm, that is 40 per cent higher than pre-industrial levels. With the current rate of increase it is estimated that the global annual average concentration will exceed 400 ppm by 2015 or 2016.
Carbon dioxide is responsible for 85 per cent of the increase in radiative forcing – the warming effect on our climate - over the past decade. Between 1990 and 2011 there was a 30 per cent increase in radiative forcing because of greenhouse gases.
United Nations Environment Programme, Press release, 14 May 2013
The Mauna Loa record, systematically zooming in to the finer more recent data