A Cape Grim milestone to focus our attention

Principal research scientist with
the CSIRO, David Etheridge.

News that Tasmania's Cape Grim weather site had recorded its first baseline reading of 400 parts per million of carbon dioxide sparked some debate over the meaning of the milestone.

As we noted ahead of the declaration of the first recording of 400ppm in the southern hemisphere, the primary greenhouse gas increase carried not much more global warming significance than, say, 399 or 401 ppm.

But as with other markers - such as Australia's foreign debt passing a $1 trillion - the 400 ppm tally helps focus our attention.

"People react to these things when they see thresholds crossed," David Etheridge, a CSIRO principal research scientist, told us. Even more upbeat was Paul Fraser, the CSIRO scientist who had helped set up Cape Grim 40 years ago. He told 9news.com.au that passing the landmark would be a "psychological tipping point".

Read Peter Hannam’s story in the Melbourne Age - “When should we worry about climate change?”