400 Fest

Lots of articles out there reflecting on the Keeling curve (daily mean CO2 concentrations at Mauna Loa) passing 400 ppmv. This is a milestone, more of  a conceptual rather than a real event, and it looks as though we are merely brushing up against 400 rather than convincingly crossing it this year.

It’s generated lots of commentary, though. For instance:

NOAA (the official statement)

On May 9, the daily mean concentration of carbon dioxide in the atmosphere of Mauna Loa, Hawaii, surpassed 400 parts per million (ppm) for the first time since measurements began in 1958. Independent measurements made by both NOAA and the Scripps Institution of Oceanography have been approaching this level during the past week. It marks an important milestone because Mauna Loa, as the oldest continuous carbon dioxide (CO2) measurement station in the world, is the primary global benchmark site for monitoring the increase of this potent heat-trapping gas.

Carbon dioxide pumped into the atmosphere by fossil fuel burning and other human activities is the most significant greenhouse gas (GHG) contributing to climate change. Its concentration has increased every year since scientists started making measurements on the slopes of the Mauna Loa volcano more than five decades ago. The rate of increase has accelerated since the measurements started, from about 0.7 ppm per year in the late 1950s to 2.1 ppm per year during the last 10 years.


ABC News (featuring Mann and Trenberth)

Something happened on Earth Thursday that scientists believe the planet hasn’t experienced in as many as three to five million years.


David Biello at Scientific American

In the coming year, Scientific American will run an occasional series, “400 ppm,” to examine what this invisible line in the sky means for the global climate, the planet and all the living things on it, including human civilization. Some scientists argue we passed the safe level for greenhouse gas concentrations long ago, pointing to the accelerating impacts, from extreme weather to the meltdown of Arctic sea ice. Others argue that we have yet more room to burn fossil fuels, clear forests and the like—but not much—before catastrophic climate change becomes inescapable. And the international community of nations has agreed that 450 ppm—linked to a rise of 2 degrees Celsius in global average temperatures—should not be exceeded. We are not on track to avoid that limit, whether you prefer the economic analysis of experts like the International Energy Agency or the steady monitoring of mechanical sensors.


Damian Carrington at the Guardian

The last time so much greenhouse gas was in the air was several million years ago, when the Arctic was ice-free, savannah spread across the Sahara desert and sea level was up to 40 metres higher than today.

These conditions are expected to return in time, with devastating consequences for civilisation, unless emissions of CO2 from the burning of coal, gas and oil are rapidly curtailed. But despite increasingly severe warnings from scientists and a major economic recession, global emissions have continued to soar unchecked.


Rod Dreher at American Conservative

I hate to say it, but I am confident that there is zero chance that we will avert this disaster. All we can do is work towards long-term adaptation and resilience.


Andrew Freedman at Climate Central

2011 study in the journal Paleoceanography found that atmospheric CO2 levels may have been comparable to today’s as recently as sometime between 2 and 4.6 million years ago, during the Pliocene epoch, which saw the arrival of Homo habilis, a possible ancestor of modern homo sapiens, and when herds of giant, elephant-like Mastadons roamed North America.


James Gerken at Huffington Post

350.org founder Bill McKibben said in a statement emailed to HuffPost, “The only question now is whether the relentless rise in carbon can be matched by a relentless rise in the activism necessary to stop it.”


Peter Gleick  at Significant Figures

The last time atmospheric CO2 was at 400 parts per million was during the ancient Pliocene Era, three to five million years ago, and humans didn’t exist.

  • Global average temperatures were 3 to 4 degrees C warmer than today (5.4 to 7.2 degrees F).
  • Polar temperatures were as much as 10 degrees C warmer than today (18 degrees F).
  • The Arctic was ice free.
  • Sea level was between five and 40 meters higher (16 to 130 feet) than today.
  • Coral reefs suffered mass die-offs.

And much more: As Robert Monroe notes: “The extreme speed at which carbon dioxide concentrations are increasing is unprecedented. An increase of 10 parts per million might have needed 1,000 years or more to come to pass during ancient climate change events. Now the planet is poised to reach the 1,000 ppm level in only 100 years if emissions trajectories remain at their present level.”


Al Gore at Huffington Post

Now, more than ever before, we are reaping the consequences of our recklessness. From Superstorm Sandy, which crippled New York City and large areas of New Jersey, to a drought that parched more than half of our nation; from a flood that inundated large swaths of Australia to rising seas affecting millions around the world, the reality of the climate crisis is upon us.

Our food systems, our cities, our people and our very way of life developed within a stable range of climatic conditions on Earth. Without immediate and decisive action, these favorable conditions on Earth could become a memory if we continue to make the climate crisis worse day after day after day.

With any great challenge comes great opportunity. We have the rare privilege to rise to an occasion of global magnitude. To do so, our communities, our businesses, our universities, and our governments need to work in harmony to stop the climate crisis.


Lou Grinzo at Cost of Energy

So, what does it mean? At one, arguably superficial level, it means basically nothing. 400ppm is no more important than, say, 395ppm or 413ppm. In fact, “400″ is a nice, round number, which tends to give it undue significance in the human mind, purely by biological accident. If we had evolved with a different number of fingers and counted in, say, base 12, then the value we associate with 400 would would be 294, and the “nice, round number” of 300 (base 12) would be 432 in our base 10 system.[1]

That piece of rampant pedantry aside, 400ppm is of extreme interest for two reasons:

First, it’s too bloody high. One can argue endlessly about what the exact right figure is, given that such a determination involves perversely squishy yet undeniably important fields like politics and economics, but I’ve yet to hear anyone who wasn’t financially or ideologically compromised claim that the ideal level was near or above 400ppm. The famous calculation by Hansen that the right answer is 350 seems about right, which makes this and the following point quite frightening. And for those who might have forgotten it, the pre-industrial level was roughly 280ppm, which makes 400 a nice, round 50% increase. [No, it’s not 50%, obviously, and it’s really about 43%. I wanted to see how many people would raise a flag over the percentage being wrong.]

Second, the CO2 level isn’t just rising, it’s doing so at a high rate. For more data than you can shake a dead computer mouse at, see the NOAA page, Trends in Carbon Dioxide. Note the scrollable list near the bottom of that page that lists the annual increases in CO2, the one that says we added a whopping 2.66ppm from 2011 to 2012. Over the last five years, our atmospheric handiwork averages a bit over 2.08ppm/year increase in CO2.


Roz Pidcock at Carbon Brief

Professor Sir Brian Hoskins from the Grantham Institute for Climate Change tells us:

“To me the striking fact is that human activity has already driven the greenhouse gas carbon dioxide to a level more than 40 per cent above the maximum levels it had during the previous million years, and it is going to stay at least this high  for thousands of years into the future.”


Michael Walsh at New York Daily News

The concentration of carbon dioxide, a harmful greenhouse gas, in the atmosphere has reached a distressing number, the highest it’s been in millions of years. Scientists warn that this is the result of man-made climate change. (sigh)


For an alternative, albeit completely incorrect, opinion check out

Jonathan DuHamel at the Tucson Citizen

Instead of fearing this artificial milestone, we should celebrate it and try to increase the atmospheric carbon dioxide concentration.

(note that the graph from E-G Beck is long-debunked nonsense)


Any more links or pithy quotes? Please add the in comments.




  1. Justin Gillis at New York Times:

    And for reverse magic, Obama's big finger to the environment:

    (am using Tenney Naumer's link as she's my main go-to on these things)

  2. Pingback: Another Week of Anthropocene Antics, May 12, 2013 – A Few Things Ill Considered

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