Within the next couple of weeks, a remote part of north-western Tasmania is likely to grab headlines around the world as a major climate change marker is passed, according to Peter Hannam at the Sydney Morning Herald:
“The aptly named Cape Grim monitoring site jointly run by CSIRO and the Bureau of Meteorology will witness the first baseline reading of 400 parts per million (ppm) of carbon dioxide in the atmosphere.”
The previous reading, taken on 6 May 2016 showed atmospheric carbon dioxide at 399.9ppm. And while levels above 400ppm have been recorded in Hawaii and Alaska, these were seasonal spikes. Carbon levels quickly dropped back again with the onset of spring:
“Cape Grim’s readings are significant because they capture the most accurate reading of the atmospheric conditions in the southern hemisphere and have records going back 40 years. With less land in the south, there is also a much smaller fluctuation according to the seasonal cycle than in northern hemisphere sites. That’s because the north has more trees and other vegetation, which take up carbon from the atmosphere in the spring and give it back in the autumn.”
Although there is little difference between carbon dioxide levels of 399.9 ppm and 400.1ppm, 400ppm is one of those milestones – like the 1.5 degrees of warming that was crossed in February – which politicians promised that we would not pass. It is further confirmation that we are on course for temperature rises well above the 2 degree limit in the Paris Agreement.