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400 Now: A Climate Change Milestone


"Puny Humans"

How many times have you heard the “Puny humans” line? You know, the one where our “littleness” is pitted against the vastness of time, or of our planet, or of the whole Universe, or occasionally against a set of powerful (but thankfully fictional) Alien Overlords?

Those who have mostly encountered it in the latter context have probably not been paying close attention to the climate debate, where it has become a ‘meme’—an apparently self-replicating thought construct that recurs and recurs. For example:

To even imagine that we puny humans on this planet can actually ‘implement’ or cause any significant ‘planetary change’ is pure senseless arrogance. That is why the whole AGW crowd is ridiculously insane and ALL a bunch of narcissistic liberals. It’s not nice to fool ‘mother nature’! (or to steal a line from Steve Martin film…”We mock what we do not understand”)

--Blog commenter “Mark_for_senate,” 2008.

It is the epitomy [sic] of arrogance to think that puny humans could do much good, or bad, to effect the weather...short of global nuclear annihilation- then it really wouldn't matter too much, would it?”

--Chester Peake, of Red Maryland Network, 2008.

Frederick Church painted this vision of 'puny humans' in the face of Nature in 1848.  Image courtesy Wikimedia Commons.

Frederick Church painted this vision of 'puny humans' in the face of Nature in 1848. Image courtesy Wikimedia Commons.

Lest I give the impression that this meme is confined to the blogosphere, it has also received airtime on mainstream media—or at least cable TV:

As old as the planet is and our puny, gnawing little humans, for seventy years we’ve changed the whole – how long have hydrocarbons been around?

--CNBC news anchor Joe Kernan, 2006.

More recently:

Compared to nature you are puny little man. There is no global warming that cannot be explained by nature. Temperatures and sea levels have not needed man’s help to rise and fall over the last 1,500 years and with out being caused by changes in atmospheric CO2 levels. Who are you little man to tell me that you believe current warming is unusual?

--“God,” as scripted by blogger “Evilincandescentbulb," 2013.

This idea doesn’t hold up particularly well to a little thought: it’s fairly easy to see that ‘puny humans’ have deforested vast stretches of the planet’s land surface, contributed to the desertification of formerly lush areas, driven numerous species to extinction through hunting or habitat destruction, increased oceanic acidity by 29%, and created vast permanent gyres of plastic waste in both Pacific and Atlantic oceans.

Plastic waste on an Indian beach gives the merest hint of the immense plastic waste gyres recirculating in both Atlantic and Pacific Oceans.  Image courtesy 'Hajj0 ms' & Wikimedia Commons.

Plastic waste on an Indian beach gives the merest hint of the immense plastic waste gyres recirculating in both Atlantic and Pacific Oceans. Image courtesy 'Hajj0 ms' & Wikimedia Commons.

New Record

Now we have a new boast—if that is the word: we have driven the atmospheric concentrations of carbon dioxide to 400 parts per million.

This milestone was announced May 10, 2015, by the two independent teams measuring CO2 concentrations atop Hawaii’s Mauna Loa, where hourly observations have been made there since 1958. The resulting time series of CO2 concentration is now generally referred to as the “Keeling Curve,” after Charles Keeling, who directed these efforts until his death in 2005. What they show is remarkable.

In 1958, measured concentrations were at 315 parts per million (ppm.) That means that in the time since then atmospheric carbon dioxide has increased by roughly 27%. But looking back to 19th-century levels of roughly 280 ppm, that increase is closer to 43%. Not an insignificant change due to us ‘puny humans.’

Yearly emissions have been increasing, too; from the 0.7 ppm per year observed in the late 1950s, they have tripled to 2.1 ppm in recent years. Dr. Pieter Tans, of the Earth System Research Laboratory at the National Oceanic and Atmospheric Administration, had this to say:

“That increase is not a surprise to scientists. The evidence is conclusive that the strong growth of global CO2 emissions from the burning of coal, oil, and natural gas is driving the acceleration.”

Image courtesy Scripps Institute, University of California, San Diego.

Image courtesy Scripps Institute, University of California, San Diego.

"400", when?

Initial reports of a daily mean above 400 ppm came from the NOAA monitoring program for May 9, 2013. But this preliminary measurement was revised downward to just below 400. However, the Scripps team observed a daily mean above 400 on May 13, as shown in the graph below. (The exact mean reading arrived at under standard protocols was 400.17 ppm.)

Interestingly, had Scripps used the same 'day' as NOAA, their mean for May 9 would have exceeded 400:

NOAA uses UTC, whereas Scripps uses local time in Hawaii to define the 24-hr reporting period. If Scripps were to use same reporting period as NOAA, we would report 400.08 for May 9.

Significance—Recent Past and Present

It is natural to ask what “400” means. In practical terms, not much—the atmosphere does not behave distinguishably differently at 400 ppm than it did at 399. But humans have a tendency to use round numbers to track our progress—or regress, for that matter. “400” is such a number.

To understand it, a little context helps. Humans have been measuring atmospheric carbon dioxide since the nineteenth century. Early methods were chemical, and were fussy, difficult, and consequently not always reliable. Still, they were made in many different types of places, from sea coasts to city streets to farmer’s fields. Swedish scientist and explorer S.A. Andrée, who had a passion for aeronautics, even took CO2 measurements in his balloon!

Collating and analyzing these measurements made it clear that although local concentrations might become elevated, perhaps from the burning of coal (as seen in some of the ‘city street’ measurements) or from biological processes (as seen in some ‘farmer’s field’ measurements), still carbon dioxide was relatively ‘well mixed’ throughout the atmosphere (as seen in those balloon-borne measurements.) Such measurements, carefully compared and analyzed, were the basis for the 280 ppm estimate given above. (This number appeared in the scientific literature in 1938, in a paper by Guy Callendar. See the sidebar for Hubs discussing his work, and some of the work of Andrée).

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Charles David Keeling changed the game. His homebuilt gas manometer had allowed him to detect the then-current baseline level of 310 ppm by 1956. With the International Geophysical Year research programs providing a temporary influx of cash, he was able to purchase from the Applied Physics Corporation infrared spectrometers developed for military and industrial use. These expensive devices would provide continuous measurements of atmospheric CO2. One was installed at a new weather observatory at Mauna Loa, the other at the “Little America” station in Antarctica.

By the end of the second year of measurements an annual cycle of CO2 was evident. Each year concentrations grow to a maximum in May, then decline slowly until early October when they once again begin to increase. The difference between maximum and minimum is about 6 parts per million. In Keeling’s words, “We were witnessing for the first time nature’s withdrawing CO2 from the air for plant growth during the summer and returning it each succeeding winter.”

So soon the levels will retreat from “400,” as plants incorporate carbon dioxide into their tissues. But of course next year’s seasonal ‘wave’ of CO2 will crest higher, carried upwards another 2 or 3 ppm. Sometime in 2015 or 2016 we’ll see the last Keeling number beginning with a ‘3.’ Ralph Keeling, Charles David Keeling’s son, and the present director of the Scripps monitoring program says:

What we're seeing right now is the beginnings of flickers up toward 400 parts per million at the iconic Mauna Loa record.

50th anniversary Mauna Loa Observatory conference and celebration, 2007, Kona, Hawaii.  Image courtesy NOAA & Wikimedia Commons.

50th anniversary Mauna Loa Observatory conference and celebration, 2007, Kona, Hawaii. Image courtesy NOAA & Wikimedia Commons.

Significance—Deeper Past

But there’s a deeper historical context—not the doings of human scientists, but the doings of the planet. When did the atmosphere last contain so much carbon?

One might look at measurements of the air trapped in micro-bubbles in ice cores. Such bubbles are found in ancient ice cores drilled from many locations around the planet. The most ancient cores give information about the atmosphere’s history as long ago as 800,000 years before the present. Unfortunately, during all that time, CO2 levels have never exceeded 300 ppm, let alone 400:

Image courtesy of the Carbon Dioxide Information Center, US Dept. of Energy.

Image courtesy of the Carbon Dioxide Information Center, US Dept. of Energy.

So scientists must resort to indirect methods for estimating CO2 in the deeper past: the analysis of ancient soils and marine sediments, for example, or to geochemical modeling. But it is thought that the last time the Earth saw “400” was during the Pliocene Epoch (5.3-2.6 million years BP.)

It was a very different world then: horses, giant beavers and camels roamed the high Arctic. Modern humans were still far in the future, but the ancestral species Australopithecus afarensis—to which the famous “Lucy” belongs—may have begun making and using stone tools to butcher meat. Global temperatures were three to four degrees Celsius warmer than at present. Worryingly, sea level was probably 10 to 20 meters higher than at present—that’s roughly 30 to 60 feet.

It seems that ‘puny humans’ are initiating a ‘new Pliocene,’ and taking the planet back to conditions older than humanity itself. But though this is unusual and striking, it turns out that this is not the first time that a species has transformed the Earth’s atmosphere. In fact, it’s far from the most striking change.

A different world:  Florida in the late Pliocene.  Image courtesy 'Noles1984' & Wikimedia Commons.

A different world: Florida in the late Pliocene. Image courtesy 'Noles1984' & Wikimedia Commons.


The Earth’s early atmosphere would have been toxic to most of today’s species. It contained virtually no free oxygen—most of the atmospheric oxygen was bound up instead in carbon dioxide and water. (Each molecule of CO2 contains two atoms of oxygen, while water contains one.) Hydrogen-containing gases such as methane and ammonia were also relatively plentiful. Breathing that, a modern mammal would be dead in minutes.

But sometime after 3.5 billion years ago, a group of archaic bacteria developed an amazing ability: we now call it “photosynthesis.” Its new metabolic patterns enabled the bacteria to use solar energy to split water and carbon dioxide apart and to combine the liberated carbon and hydrogen to make useful chemicals—and to power their metabolisms. The resulting waste oxygen was ejected into the atmosphere.

Since this new metabolic pathway was highly efficient, these ‘cyanobacteria’ were able to compete with great success against other organisms. Their numbers increased, and the oxygen emissions increased accordingly.

For a long time, the oxygen was quickly taken up by the weathering of iron—great bands of iron oxide—rust—were laid down in the geological record. But after long eons of this, natural oxygen sinks began to fail. Oxygen levels began to increase rapidly.

Cyanobacteria under the microscope.  Image courtesy 'iceclanl' & Wikimedia Commons.

Cyanobacteria under the microscope. Image courtesy 'iceclanl' & Wikimedia Commons.

Wikipedia has this to say about the upshot of the “Great Oxygenation Event”:

Free oxygen is toxic to anaerobic organisms and the rising concentrations may have wiped out most of the Earth's anaerobic inhabitants at the time. From their perspective it was a catastrophe. Cyanobacteria were therefore responsible for one of the most significant extinction events in Earth's history. Additionally the free oxygen reacted with the atmospheric methane, a greenhouse gas, reducing its concentration and thereby triggering the Huronian glaciation, possibly the longest snowball Earth episode. Free oxygen has been an important constituent of the atmosphere ever since.

One must presume that there were no cyanobacteria scientists—no-one to identify the process in which the cyanobacteria were enmeshed; no-one to extrapolate trends; no-one to make predictions or issue warnings. Nor could there have been cyanobacteria bloggers, ready to point out that cyanobacteria were tiny creatures, beings whose puniness in the face of an enormous planet and time spans was even more marked than that of H. sapiens.

A cast of the remains of 'Lucy.'  Photo courtesy '120' & Wikimedia Commons.

A cast of the remains of 'Lucy.' Photo courtesy '120' & Wikimedia Commons.


Humans are of course much, much more complex that cyanobacteria—most people would certainly regard the cyanobacteria as a humbler order of creature altogether. And yet, not only have we yet to demonstrate that we are any more in control of our actions—and thus our fate—than were the cyanobacteria, but the possible catastrophe that we precipitate will almost certainly be less significant and have less long-lasting effects.

At creating mayhem, we will have been outdone by an archaic group of unicellular animals.

But perhaps this can help remind us what arrogance is, and is not. Above the door of the ancient Delphic shrine was engraven a succinct maxim that is still proverbial wisdom. Plato put it in Socrate’s mouth, but it is almost certainly older still: Know thyself.

Puny as we may be, we can create very large consequences. We know this to be true, because even punier creatures than we have done so before.

To “Know thyself” is a virtue, by general consensus. But it is also a survival trait. To close our eyes to the evident consequences of our actions on the pretext of ‘humility’ is neither virtue, nor conducive to survival. “400” reminds us of that. May we have the humility to attend to the lesson.

A 1st-century Roman media bearing the Greek motto:  "Know thyself."  Image courtesy Michael Hurst & Wikimedia Commons.

A 1st-century Roman media bearing the Greek motto: "Know thyself." Image courtesy Michael Hurst & Wikimedia Commons.

  • CO2 Now | CO2 Home
    A portal for all things atmospheric CO2. Check the latest concentration numbers here.

Update: 4/29/15

The Scripps monthly value for March, 2015, came in at 401.52 ppm. It's the first March which has had a monthly value of 400 or greater. (In 2014, three months--April, May, and June--exceeded that threshold.)

We'll have to wait a bit to see how this year pans out, but clearly the rise remains an ongoing feature of contemporary life.

Update: 9/28/16

With the 'rising CO2' part of the year ready to kick in, it is now inevitable: 2016 is the first calendar year in human experience in which atmospheric concentrations of CO2 have not dipped below 400 ppm.

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Doc Snow (author) from Camden, South Carolina on May 23, 2013:

I know what you mean. Unfortunately, that's rather a pattern; we got the same thing with the drought coverage last year. Many stories never mentioned the connection at all--and of course, that one is very solid, at least in a couple of senses.

At least President Obama has decided that a little 'bully pulpit' action on climate change isn't such a bad thing in his second term:


That's an important study to highlight, too, since it demonstrates so starkly how strong the actual scientific consensus is.

i scribble on May 23, 2013:

Yes, that's what I'm hearing and reading as well, mostly on the internet. Chris Hayes (MSNBC) did interview a climate expert Tues. night on his show who said basically the same thing. I think he said technology will allow the smaller scale models in the near future. Another issue is inadequate record keeping on tornadoes over the longterm. I fully expect a connection will be proven in the next couple of years. Still it's frustrating when the issue of climate change isn't even brought into the discussion in any of the major network coverage (at least that I saw) of the tornadoes.

Doc Snow (author) from Camden, South Carolina on May 22, 2013:

Further to the last couple of comments, today's DotEarth (NY Times) had an extended discussion of tornadoes and climate change. It seems the science is still pretty inconclusive:


Doc Snow (author) from Camden, South Carolina on May 21, 2013:

Thanks, i scribble.

"Feeling frustrated that no one seems to be making a connection between the OK super tornadoes and climate change. The silence is deafening."

Partly that's because that area of the science is (as I understand it at least) still pretty unsettled. Just tonight there was this exchange on RealClimate:


But the connections still seem unclear, though intriguing. I seem to recall that part of the problem is that it's hard to model weather on a small enough scale.

Still, the basic fact that the atmosphere is now quite a bit moister, on average, suggests that all sorts of convective storms could be getting stronger accordingly--and that would include tornadoes.

i scribble on May 21, 2013:


Just want you to know that I perused, absorbed, appreciated and agreed with the totality of your words and ideas here. Feeling frustrated that no one seems to be making a connection between the OK super tornadoes and climate change. The silence is deafening.

Doc Snow (author) from Camden, South Carolina on May 20, 2013:

The first and second email batches contained conversations among "scientists" documenting that their claims of a man-made global warming crisis were deliberately contrived for career gain, research funding and "the cause," as climate scientist Michael Mann calls it."

But I've read a lot of the emails in the raw, and have, I am sure, read every single one that was alleged to be "incriminating." I've never seen one that even suggested (let alone documented) that any conclusion was "contrived," deliberately or otherwise, for either career gain or research funding. And I've never seen anything that shows that any of the scientists involved disbelieved any of their own conclusions at the time that they were making them.

If you know of something specific that does so, I'd appreciate a pointer to it. But Mr. Arnold's musings don't cut it--they are vague, unsubstantiated, and occur in the context of a piece that is labeled "opinion." (Correctly, I'd say.)

Doc Snow (author) from Camden, South Carolina on May 20, 2013:

? The first appears to be a series of communication strategies for climate change activists, none of which go to questions of content. Interesting in itself, but not much to your point, or so I would think.

The second didn't work, even though I tried several variations of your link.

Jim Lyde from Austin, Texas on May 20, 2013:



Doc Snow (author) from Camden, South Carolina on May 20, 2013:

You are welcome. But who exactly do you think deceived someone, when, and how? I don't find that the discussion at SkS shows that there was any deceit--or clearly articulates just why those who thinks so hold that opinion.

Jim Lyde from Austin, Texas on May 20, 2013:

Thanks, Doc. I was going to post some links, but I see that the commenters to the article you posted ("skeptical science") did a much better job that I would have. I still maintain that intentional deception occurred.

Doc Snow (author) from Camden, South Carolina on May 20, 2013:

LibertyCell, I am afraid you have been misinformed. Several independent inquiries found that no scientific misrepresentations occurred. You are probably referring to this incident:


In short, "trick" meant an "elegant technique" (as in 'trick of the trade'), not a "deception."

Moreover, the basic "hockey stick" shape of paleoclimate temperatures as been shown to be real in numerous studies carried out since the original "hockey stick" paper in 1999. The most recent is this one:



A summary of some of the other work replicating the 'hockey stick' is here:


If you are interested in Dr. Mann's take on the hockey stick controversy, I've written about his book on the topic here:


As to 'integrity,' perhaps a hint for us is found in the very incident you seem to be referring to: *someone* illegally hacked and stole that correspondence; after which several "someones" in the blogosphere hyped a small number of out-of-context quotes while assiduously ignoring numerous other passages making quite clear the scientists' sincerity in their views, going so far as to repeatedly claim 'fraud' in the face of conclusive evidence to the contrary.



Jim Lyde from Austin, Texas on May 19, 2013:

Climate change is occurring, as it has always been occurring. At least some of those in the scientific community charged with investigating how much of that is man made as opposed to the work of Mother Nature have provided a horrible disservice. Those whose work resulted in the "hockey stick" graph, shown to be fraudulent by the correspondence of the scientists themselves, have created even more skepticism. If we could inject some integrity into players on all sides, we would be a lot better off.

Doc Snow (author) from Camden, South Carolina on May 18, 2013:

Good analogy, too. The bottom line is, follow the facts, not the emotional 'tag'.

There's something called the "argument from consequences," which essentially boils down to "it would be too terrible if this were true, therefore it is false." Obviously, that's emotionalism, not logic. I think the 'puny humans' meme is just another instance of this, and a particularly dishonest one. My emotional reaction to it is to be infuriated by the attempt to hijack the virtue of humility!

John Coviello from New Jersey on May 18, 2013:

I like to use the ant analogy. Ants are puny creatures that on their own and in small numbers change their environmental very little, if at all. However, if colonies of ants take over a wooded area, they can seriously change their very localized environment, by deforesting a small wooded area. The same could be said of humans. It is the collective actions of billions of "puny" humans each contributing to global warming in their tiny way that can affect the Earth's atomosphere and environment.

Doc Snow (author) from Camden, South Carolina on May 17, 2013:

Thanks, Orin.

You may well be right, for some pushing this meme, at least. "What was that about those who will not see?"--or will not to see!

I find it ironic that the idea that humans can affect climate is pilloried as arrogance, but the inverse idea--that we can do whatever the hell we want to, with no consequences whatever--is not. In most contexts, we'd call such an attitude incredibly 'entitled,' which is at least next door to arrogance.

P. Orin Zack on May 17, 2013:

Nice piece, Doc. I suspect that the 'puny humans' perspective is an artifact of a worldview in which only an omnipotent creator-god has the power to affect an entire planet, so claiming that humans are responsible for such a thing becomes a heresy to them. Somehow, they manage to hold this in their minds at the same time they experience the ability to control a machine many times their size and weight with just the tap of a foot and the flick of a wrist. What was that about those who will not see?

Doc Snow (author) from Camden, South Carolina on May 17, 2013:

Very cool, water geek! I will check that out. We've made some lifestyle changes to bring down our household carbon footprint, but feel that there is surely more that we can still do to support the all-too-slow process of changing our energy economy.

Individual changes surely can't get the job done, but somebody has to 'pioneer' low-carbon lifestyles; to show leadership; to demonstrate that no, you don't have to live in a cave to lower your carbon footprint; and to contribute that (small, but not thereby insignificant) emissions reduction to the total needed. And surely supporting each other in doing so is really crucial.

Susette Horspool from Pasadena CA on May 17, 2013:

Well written, Doc. There are schools, cities, and churches all over the US now starting to divest their funds from fossil fuels industries and apply them elsewhere. Also, do you know about the international Transition Movement? It's a growing group of concerned citizens creating new ways of living with a minimum of fossil fuels. We have a local chapter here in Pasadena CA. They promote local food production, time banking, fairs for craftspeople to repair damaged goods, and riding bicycles instead of cars. Here is the Transition Network's website: http://www.transitionnetwork.org/

Doc Snow (author) from Camden, South Carolina on May 16, 2013:

There is reason to be concerned. It's not only marine clathrates, it's also methane in permafrost and the like. Arctic levels have been trending up for a while, and while it doesn't look like catastrophe just yet, it certainly can't be good. We've got to get our act together.

John Coviello from New Jersey on May 16, 2013:

We reached that 400 ppm CO2 milestone Mauna Loa a couple of years earlier than I expected it to be reached, which is kind of disturbing. I was thinking 2015. Just wait until all that CO2 warms the Earth's atmosphere up enough to start releasing frozen methane (CH4) from the depths of the oceans and from the polar regions. Then, we might just see the Earth boil over. It's CH4 that really concerns me.

Doc Snow (author) from Camden, South Carolina on May 16, 2013:

Thanks for reading my thoughts on this ominous milestone. What do you think about reaching "400," albeit as a May "flicker?"

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