Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Kevin Bullis

A View from Kevin Bullis

New Milestone for CO2 Levels: Mauna Loa Observatory Records 400 PPM

We’ve hit 400 ppm of carbon dioxide, but we won’t know what that means for decades.

  • May 10, 2013

The National Oceanic and Atmospheric Administration and Scripps Institution of Oceanography say that the carbon dioxide concentration in the atmosphere hit the symbolic milestone of 400 parts per million yesterday, up from about 280, the level it was at for thousands of years before the Industrial Revolution.

There are two things to keep in mind about carbon dioxide. First, it stays in the atmosphere for a long time—hundreds to thousands of years. If we stopped burning fossil fuels today, the concentration of carbon dioxide will start falling, but it will take over a thousand years to get back to pre-industrial levels (see “Climate Change: The Moral Choices”).

The second is that it takes a long time for the earth to respond to higher levels and reach a new state of equilibrium. So we won’t know for many decades—or even over a hundred years– what impact 400 parts per million will have.

That means that, while it will be a long time before we know what 400 parts per million will do to the planet, whatever it does we’ll be stuck with for a long time.

Here’s the takeaway from Scripps:  “There’s no stopping CO2 from reaching 400 ppm,” said Ralph Keeling [a geochemist at Scripps ]. “That’s now a done deal. But what happens from here on still matters to climate, and it’s still under our control. It mainly comes down to how much we continue to rely on fossil fuels for energy.”

Couldn't get to Cambridge? We brought EmTech MIT to you!

Watch session videos here
More from Sustainable Energy

Can we sustainably provide food, water, and energy to a growing population during a climate crisis?

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.