400 Now: A Climate Change Milestone

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.

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.

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 19^th-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.”

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.

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).

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.

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:

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.

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.

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.

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.

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.

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.