Australian Broadcasting Corporation: Global greenhouse gases in the atmosphere have reached an ominous milestone that's unprecedented in recorded human history.
At the Mauna Loa observatory in Hawaii, the daily reading of carbon concentrations has now reached a level that hasn't been seen in more than 3 million years: CO2 levels in the atmosphere have hit 400 parts per million.
The last time it reached a level like this, temperatures rose from between three and four degrees and sea levels were between five and 40 metres higher...