Climate Change

Published on May 13th, 2013 | by Dr. Karl-Friedrich Lenz


Why The 400 PPM Milestone Is Irrelevant

May 13th, 2013 by  

This article was originally published on Lenz Blog.

There are multiple people on my Twitter timeline mentioning the fact that CO2 levels have passed 400 ppM for the first time. Let’s just point to this well informed and interesting explanation by Peter Gleick on Scienceblogs, titled “The Last Time Atmospheric CO2 was at 400 parts per Million Humans Didn’t Exist.”

As Gleick explains, 400 ppM means an ice-free Arctic, average temperatures up between 3 and 4 degrees Celsius, and over 10 degrees at the poles, sea levels between 5 and 40 meters higher.

So why do I think this is irrelevant?

The answer is easy.

Anyone paying attention knew a long time ago that we will reach 400 and blow right past it. The fine people at want humanity to keep CO2 levels under 350. That is not likely to happen any time soon.

To explain this with a little comparison to Bitcoin, it didn’t matter much if the price was at $2 or at $5 some time in 2011. It was always sure to go way up anyway (it is around $110  now).

The one thing that matters most is if humanity somehow will be able to avoid the positive feedback spiral leading to Venus syndrome. This question has only two possible answers.

In contrast, assuming stabilizing at some level or other of global warming, that is a question of degree. While much would change, there would still be at least some life left on the planet, possibly even human life.

For all of that, blasting through 400 ppM is not ever so important. The real fight will come in the next couple of decades.

Check out our new 93-page EV report, based on over 2,000 surveys collected from EV drivers in 49 of 50 US states, 26 European countries, and 9 Canadian provinces.

Tags: , , , , ,

About the Author

is a professor of German and European Law at Aoyama Gakuin University in Tokyo, blogging since 2003 at Lenz Blog. A free PDF file of his global warming science fiction novel "Great News" is available here.

  • I agree with the author. The rate of Human shift to renewables is MUCH FASTER than the rate of rising PPM.

  • bob

    For a couple months now, most of the windmills on the old Bethlehem Steel property haven’t been turning at all.

  • We won’t change our growth dependent economic model which means we’ll feed our economies with dirty cheap energy for decades to come… the growth model has to change.


    • Bob_Wallace

      The dirtiest of our energy sources are coal and oil.

      They are also produce more expensive energy than the energy sources we’re starting to use to replace them.

      Wind, solar, geothermal, hydro and (likely) tidal produce cheaper electricity than does coal. (Remember the health costs of coal.)

      It’s about one-fourth as expensive to drive with electricity than using oil.

      We can grow all we want as long as the inputs are sustainable and we don’t harm ourselves with the byproducts.

      • Alan kemp

        Australia has closed a number of coal power station with good results levels of reduction in CO2 emissions one power station has reported in SA down by 85 per cent.

        Australia has done its part.

      • Ross

        This point about sustainable growth needs to be more widely understood.

        • Bob_Wallace

          I think we hurt our progress away from fossil fuels by making people afraid that they will have to radially change their lifestyle and perhaps have to suffer due to a greatly diminished economy.

          I think we need to be telling people that they can have it all as long as we get the hell away from fossil fuels and make some changes to our manufacturing feedstock.

  • photosymbiont

    Just one little point – the Venus outcome is completely implausible, please remember the atmospheric pressure there is much much higher than on Earth. We’ll have plenty to worry about – massive population movements, severe drought and flooding, major circulation shifts, etc etc without invoking scientifically implausible outcomes like a “runaway greenhouse”. It’s not going to happen.

    Sometimes it seems that the renewable energy communities and the climate science communities need to talk to one another a bit more. Then you wouldn’t have such mistakes being made (and you’d see fewer climate scientists promoting similarly implausible concepts like “zero-emission” coal plants and the like, too).

  • James Wimberley

    This is deeply misguided politically. Humans rally round slogans and symbols. A good cause rallies round a symbol that encapsulates a more complex truth. That’s why 400ppm matters. We’ve just gone through a red light, at speed. WHOA!

  • Kevin Adams

    The flora are going to love this… plants need CO2 and warmth. Perhaps increased flora growth will cycle out the excess CO2 and give us more oxygen in the process. But in the meantime, will Arizona finally have ocean-front property?

    • Bob_Wallace

      Extra plant growth in one area is likely to be offset by plant extinction/desertification in others.

      Arizona will likely have a mass exodus long before the ocean arises….

      • Tim

        No more renewable energy is the only way.

    • photosymbiont

      Yeah, I think plants need the right amount of water more than they need a extra bump of CO2, don’t they? Flooding and drought are what threaten agriculture, and in any case, CO2 is never a limiting nutrient for plant growth – that’s why fertilizers include nitrates and phosphates, right?

      It really is a tired old scientifically inaccurate talking point based on a ludicrous simplification of plant physiology.

  • Ross

    It is a fight worth having. It’s going to get ugly as the earth responds. Drill down a few metres in Greenland and you’re at a point out of equilibrium with the current level of CO2 in the atmosphere. Even if we could slam things into reverse and get off fossil fuels in the next 20 years the world is going to keep warming up 🙁

Back to Top ↑