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Global CO2 Breaches 400 PPM

Climate Science: The atmospheric concentration of the greenhouse gas surpasses a milestone level, one not matched in millions of years

by Stephen K. Ritter
May 18, 2015 | APPEARED IN VOLUME 93, ISSUE 20

Credit: NOAA

Chilean meteorologist Patricio Eladio Rojas Ledezma prepares to collect air samples with a portable monitor on Easter Island as part of NOAA’s Global Greenhouse Gas Monitoring Network.
Credit: NOAA

Chilean meteorologist Patricio Eladio Rojas Ledezma prepares to collect air samples with a portable monitor on Easter Island as part of NOAA’s Global Greenhouse Gas Monitoring Network.

Scientists who operate the National Oceanic & Atmospheric Administration’s Global Greenhouse Gas Reference Network report that Earth’s global average atmospheric carbon dioxide level surpassed 400 ppm in March. NOAA bases the global CO2 average on air samples taken at 40 remote sites around the globe and analyzed at its Earth System Research Laboratory in Boulder, Colo. The NOAA team first recorded levels above 400 ppm at some sites in 2012, but now the average for all reporting stations is above the mark. The last time Earth’s atmospheric CO2 level reached 400 ppm is thought to have been during a peak warm period roughly 4.5 million years ago, which scientists have deduced from a combination of analytical instrument readings since the 1950s and proxy data from ice cores and other sources. The CO2 level was hovering around 280 ppm prior to the Industrial Revolution in the mid-1800s, but the level has been creeping up because of the increased burning of fossil fuels. The data show that half of the 120-ppm increase since 1850 has occurred after 1980 and that the growth rate is increasing and now stands at 2.25 ppm per year. The scientists note that the global average fluctuates seasonally as vegetation and soil organisms wax and wane, but the overall trend continues upward.

NOAA scientists have tracked atmospheric CO2 concentrations since 1980. SOURCE: NOAA
NOAA scientists have tracked atmospheric CO2 concentrations since 1980. SOURCE: NOAA


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Larry (May 18, 2015 12:07 PM)
Steve Ritter (May 20, 2015 2:16 PM)
Note: Larry's reference points to a temperature trend based on proxy data from satellite measurements in the atmosphere. NASA's GISS data show that global average surface temperature has increased 0.2 C over the same period, with 2014 being the warmest year in modern times (
L.W. Sumansky (May 20, 2015 3:14 PM)
I do not see any mention of the amount of CO2 given off by the active volcanoes. It has been stated that Mt. Helens eruption a few years go, increased the CO2 level by
as much as 10 ppm for a period of time. The current eruption of a volcano in Chile
is surely contributing to currently measured amounts.
Steve Ritter (May 21, 2015 4:18 PM)
That's a good question with a surprising answer. Human activities are responsible for roughly 35 billion metric tons of CO2 emissions per year (in 2010), whereas all of Earth's geological degassing is roughly 0.2 billion metric tons per year (in 2011). Kīlauea volcano in Hawaii has an annual CO2 output of about 0.003 billion tons per year. And Mount St. Helens put out 0.01 billion tons in 1980. You can read more about it here:
g gill (May 20, 2015 7:20 PM)
Projection of this data as an exponential curve should serve as a predictive trend for future. The consequences of doubling the pre industrial level by 2035, could mean catastrophic events.
J. A. Budny (May 21, 2015 5:53 PM)
By "catastrophic events" exactly what do you mean?
P Hamann (May 22, 2015 11:42 AM)
The curve is roughly linear, not exponential. However, the effects from this linear increase are certainly not linear in the long run.
Edgar Mueller (May 21, 2015 8:50 AM)
The raising CO2 concerntration in the atmosphere is certainly related to the human burning of fossile fuels (carbon, oil, gas), but not exclusively. Other technology related issues, like construction activity (concrete making involves the reaction of CaCO3 with SiO2, producing silicates and CO2) and the production of iron and aluminum, contribute also to the increase of atmospheric CO2. The hugest potential CO2 reservoirs on Earth are not the fossile fuels, but the carbonate rocks of many mounain massives (hundreds of thousands of kilometer-cubes!).
On the other hand, atmospheric CO2 is used up by the green plants as their (only!) source of carbon for synthesizing organic material. Plants grow the rapider (i.e. with a more efficient photosynthesis) the higher the level of atmospheric CO2 is; their growth optimum lies far above the concerntration which is tolerable for human beings. Most market gardeners add CO2 to the atmosphere in their greenhouses, in order to accelerate the vegetable growth therein.
We should also consider that the Earth atmosphere is not a greenhouse, wherein a glass window impedes convection and allows the inside to become quite hot when the sun radiation heats up the ground. The Earth atmosphere, if heated up at the ground, installs vertical convection: the hot gas expands, becomes lighter, and raises up to the stratosphere, where it cools down again by thermal radiation loss into space. Water condenses then and falls out as rain. This is the motor of the weather phenomena. Due to the Earth rotation, this vertical convection also produces horizontal convection (cyclones, anticyclones) by means of the Coriolis forces. Horizontal convection carries evaporated water from the Oceans into the continents, such that it rains and green may grow everywhere (necessary for our survival; otherwise the interior of the continents would be desertic).
Increased convection is the most significant effect of an increased CO2 concentration in the Earth atmosphere: we have now more and stronger winds and storms, and stronger temperature fluctuations than before; hot air from the Sahara region may now be drawn northwards to the Alps, melting down there the eternal snow, and snow may now fall in northern Africa and in Israel. The interiors of the continents get much more water than 100 years ago, and Planet Earth is generally greening up. Even the Sahara desert might, if increased convection carries more water into it, get green again, as it was 10'000 years ago.
On the other hand, the direct surface temperature increase on Earth due to the increased CO2 concentration is a merely secondary effect; the most important greenhouse gas in the Earth atmosphere being water vapor anyway. CO2 has only a small spectral coverance, compared to water, and is present in small concentration in the atmosphere, compared to the concentration of water. The thermal energy balance of the Earth atmosphere must noteworthy be assessed with comprehensive view and in a quantitative way; one may not focus on a single element and judge it outside its context.
Robert Buntrock (May 24, 2015 1:04 PM)
Recent research has shown a non-linear relationship between atmospheric CO2 concentrations and their effect on plant growth. The accelerated growth decreases at CO2 levels not that much above ambient. The optimum is not that far above "what is tolerable by humans" (whatever that means). The effects of increased CO2 have far greater impact on the environment including ocean acidification (and it's effect on aquatic shells). Granted water and water vapor are the atmospheric wildcards but the water cycle is far more rapid than the CO2 cycle. As for rainfall, that's very spotty and dependent on other factors such as El Nino. Please cite your data on a worldwide basis. Increased global temperatures will increase the likelihood of extreme weather of all kinds.
Joao Poco (May 21, 2015 10:12 AM)
Geological data show that naturally high carbon dioxide concentration in atmosphere occurs at the end of interglacial periods. In this current interglacial the mankind contribution is evident. What will happen next, warm or cold period?
Steve Ritter (May 26, 2015 12:48 PM)
Interesting question. One thing the temperature trend over the past few hundred thousand years shows is that the temperature goes up and down with the glacial cycles and the CO2 levels go up and down. But after the global temperature rose after the last glacial period, the temperature reached a plateau, and instead of starting to go down again, it is now rising. You can read more about it here:
john j skiffington (May 21, 2015 4:38 PM)
much more data should be parsed and published, such as the heating of the North's methane deposits that evolve into CO2 exponentially with the increase of energy in the fragile atmosphere, the CO2 produced by the earth's increasing fauna population not only its use of fossil fuel but also its breath, and that further exacerbated by its deforestation especially by fire (brazil and Indonesia), oil and other chemical spills that ruin ocean organisms to produce oxygen and thus the creation of dead zones that promote oncogenes and toxins to further complicate the atmosphere and earth such as the Great Pacific Garbage Patch which ruins the fish population. john j skiffington acs Woonsocket ri.
Steve Ritter (May 22, 2015 11:45 PM)
This C&EN article about methane emissions from a year ago has some of that information:
J. A. Budny (May 21, 2015 5:59 PM)
If the CO2 levels reached 400 ppm 4.5 million years ago and humanity is only 2.8 million years old, why is NOAA making a reference to the Industrial Revolution and implying that the current rise in CO2 is due to human and commercial activity? Could it be an attempt to spread fairy dust or play shell games in an attempt to make everyone think that the rise in CO2 levels is anthropogenic? What evidence, not ideological babble, just simple plain, old-fashion logic, supports the impossibility that the 400 ppm of CO2 today comes from a different source from the 400 ppm of CO2 4,5 million years ago when the Industrial Revolution couldn't even achieve "thought" status?
P hamann (May 22, 2015 11:51 AM)
This, and many other issues, have been addressed. The climate history of the Earth is long and complex, but our current problem is, indeed, rising CO2 levels. Go to to find a more complete answer to your question.
Robert Buntrock (May 24, 2015 1:10 PM)
Regardless of the source of the increased CO2 in prior geological ages (and there are theories on how that occurred--check recent articles in nature and Science) but recheck the rapid rate of increase in the last couple of centuries and correlate with increased industrial and combustion activities. Inclusion of insulting denigrations like "fairy dust" puts one more in the ranks of the deniers (and not skeptics) and has a negative impact on the credibility.

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