Cape Grim numbers are just that: 'grim' as they pass 400ppm

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.

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, researchers predict.

"Once it's over [400 ppm], it won't go back," said Paul Fraser, dubbed by CSIRO as the Air Man of Cape Grim, and now a retired CSIRO fellow. "It could be within 10 days."

The most recent reading on May 6 was 399.9 ppm, according to readings compiled by the CSIRO team led by Paul Krummel that strip out influences from land, including cities such as Melbourne to the north.

Read Peter Hannam’s story in today’s Melbourne Age - “Global warming milestone about to be passed and there's no going back.”

(Interestingly, it was less than two years ago when the Shepparton-based Slap Tomorrow organized to have the Cape Grim figures displayed publically, but that has now changed and they are numbers from the Mauna Loa observatory monitored by NOAA. The Cape Grim figures then were about 395 parts per million (PPM) and that number is about to exceed 400ppm. At Mauna Loa, the number is nearly 405ppm – Robert McLean.)