Wow. Our experiment is off to a great start—let's see if we can finish it off sooner than expected.
Well, we finally did it. We hit a new carbon dioxide milestone yesterday:
Scientific monitors reported that the gas had reached an average daily level that surpassed 400 parts per million — just an odometer moment in one sense, but also a sobering reminder that decades of efforts to bring human-produced emissions under control are faltering.
The best available evidence suggests the amount of the gas in the air has not been this high for at least three million years, before humans evolved, and scientists believe the rise portends large changes in the climate and the level of the sea.
This is from NOAA. The reading from the Scripps instruments for yesterday was 399.73 because they use local time, not Greenwich time. This gives them a slightly different 24-hour window that defines a "day."
But not to worry. They'll hit 400 soon too. And by next year, pretty much every day will be above 400. Congratulations, homo sapiens!