Counting Down to 400 ppm

April 30, 2013


Some hourly readings at Mauna Loa now above 400 ppm.

Sidney Morning Herald:

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 looks like the world is going to blow through the 400 ppm level without losing a beat,” said Ralph Keeling, a geologist with the Scripps Institution of Oceanography in the US, which operates the Hawaiian observatory.

”At this pace we’ll hit 450 ppm within a few decades.”

The 450 ppm level is considered to be the point at which the world has a 50 per cent chance of avoiding dangerous climate change. Any higher and the odds of avoiding searing temperature rises of 4 or 5 degrees by the end of the century become prohibitively risky.

The rise in greenhouse gases corresponds with the extra amount of CO2 known to have been emitted by human activities, such as burning fossil fuels and cutting down forests. More greenhouse gases means more heat builds up at the Earth’s surface.


8 Responses to “Counting Down to 400 ppm”

  1. Especially ‘Liked’ the renaming of the Australian newspaper!

  2. Jean Mcmahon Says:

    When something really bad happens I go out and buy a Buddha Statue…Doesn’t seem to help

  3. joffan7 Says:

    We are also going to blow through the 410 and 420 ppm lines on the graph without missing a beat. The existing, built-in carbon emissions will not change significantly on that timescale, which I project will be within the next ten years. Unfortunately there is little chance of significantly postponing the next two multiples of ten either.

  4. Peter Mizla Says:

    400ppm is now- we have to expect from this over the-long haul 2 degrees C warming- the inertia in the climate system will not kick in fast enough for us to see the really bad stuff with climate change- and by then it will of course be too late.

  5. […] basis how the plankton stocks are doing?” Same with CO2 levels, which are teetering at close to 400 ppm this week. “We don’t have public conversations about […]

  6. astrostevo Says:


    I am surprised given that the CO2Now website had last month at 397 ppm.

  7. astrostevo Says:

    350 ppm is supposedly the “safe” limit. See :


    “Remember This: 350 Parts Per Million” by Bill McKibben


    350 PPM CO2: Earth’s Tipping Point? – Bill McKibben

    from Fora talk May 6th 2009 when the Co2 level was 387 ppm and also coincidentally in Sydney, Australia.

    Read about this also in Hansen’s excellent ‘Storms of My Grandchildren’ (Bloomsbury Publishing 2009.) especially chapter 8 starting page 140.

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