Last time CO2 was this high, our ancestors were using stone tools

Caught this in yesterday's SMH: Carbon dioxide concentrations in the Earth's atmosphere are on the cusp of reaching 400 parts per million for the first time in 3 million years.  The daily CO2 level, measured at the Mauna Loa Observatory in Hawaii, was 399.72 parts per million last Thursday, and a few hourly readings had risen to more than 400 parts per million. ''I wish it weren't true but it