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Human CO2: Peddling Myths About The Carbon Cycle

Posted on 29 August 2010 by gpwayne

Before the industrial revolution, the CO2 content in the air remained quite steady for thousands of years. Natural CO2 is not static, however. It is generated by natural processes, and absorbed by others.

As you can see in Figure 1, natural land and ocean carbon remains roughly in balance and have done so for a long time – and we know this because we can measure historic levels of CO2 in the atmosphere both directly (in ice cores) and indirectly (through proxies).

Figure 1: Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons (Source: Figure 7.3, IPCC AR4).

But consider what happens when more CO2 is released from outside of the natural carbon cycle – by burning fossil fuels. Although our output of 29 gigatons of CO2 is tiny compared to the 750 gigatons moving through the carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra CO2. About 40% of this additional CO2 is absorbed. The rest remains in the atmosphere, and as a consequence, atmospheric CO2 is at its highest level in 15 to 20 million years (Tripati 2009). (A natural change of 100ppm normally takes 5,000 to 20,000 years. The recent increase of 100ppm has taken just 120 years).

Human CO2 emissions upset the natural balance of the carbon cycle. Man-made CO2 has increased  atmospheric CO2 by a third since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO2 is a very small component of the global carbon cycle, the extra CO2 is cumulative because the natural carbon exchange cannot absorb all the additional CO2.

The level of atmospheric CO2 is building up, the additional CO2 is being produced by burning fossil fuels, and that build up is accelerating.

This post is the Basic version (written by Graham "The Machine" Wayne) of the skeptic argument "Human CO2 are a tiny percentage of CO2 emissions". We're currently writing plain English versions of all the skeptic rebuttals. If you're interested in helping with this effort, please contact me

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Comments 1 to 16:

  1. "Man-made CO2 in the atmosphere has increased by a third since the pre-industrial era" I think you mean "Man-made CO2 has increased the overall level of CO2 in the atmosphere by a third since the pre-industrial era".
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  2. Also, where's the data behind "A natural change of 100ppm normally takes 5,000 to 20,000 years."? I ask because delayers like my local MP say we're just "accelerating" natural climate change. But by what factor? Joe Romm claimed 14,000 times, but that's compared to the trend over the last 600,000 years (22ppm), not to the maximum natural rate of change.
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  3. jondoig: good call on the first point - I'll amend that straight away. On the second point, it's from Tripati 2009 (quoted from the intermediate version).
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  4. Another bug getting the upper hand - Coffee threatened by beetles in a warming world A tiny insect that thrives in warmer temperatures — the coffee berry borer — has been spreading steadily, devastating coffee plants in Africa, Latin America, and around the world
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    Response: Global warming threatening my coffee? This time its personal!
  5. Can someone prove it is manmade CO2 that is being added or just extra CO2 since the planet has been warming for the past 30+ years? During periods of warming, more CO2 will be naturally released by vegetation decomposition, etc. It may take nature time to readjust the feddback cycle.
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  6. Nerndt, that is explained in the Intermediate version of this post. In the green box at the top of this page, click the link to "Human CO2 are a tiny...." Once on that page, click the Intermediate tab.
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  7. What's so special about the past 20millions years? 100 million years ago pCO2 was three times it is today. 175 million years ago it was 7 times todays level. What is "the natural balance of the carbon cycle"? It seems like an unscientific statement. I can't imagine anything that is working for balance in this.
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  8. #7: "100 million years ago pCO2 was three times it is today. 175 million years ago it was 7 times todays level." Point being? Don't neglect to mention that there was far more widespread volcanic activity during the Cretaceous than today. And highly variable climate as well. Although I hesitate to reference other blogs, this guy's pretty good with volcanoes. Of course that would suggest that CO2, whether 'natural' or emitted by fossil fuel use, influences climate in a GHG kind of way. So your comment suggest that you've come to accept the 'GHG hypothesis'?
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  9. "100 million years ago pCO2 was three times it is today. 175 million years ago it was 7 times todays level." I understand why people raise this point, but if you think it through, you'll realize that the fact that a certain condition existed millions of years ago, prior to the entire period of the establishment and development of human civilization, does not mean that that condition isn't extremely dangerous and destructive, and an extreme change from the conditions that have existed for the thousands of years in which human societies have flourished. Suppose, for example, somebody said to you: "Who cares about nuclear war? Many times in the earth's history, we've been struck by giant meteors that exploded with the force of thousands of nuclear bombs. So what if it happens again?" I'm sure you understand my point: the earth has existed for billions of years. Just because something has an analogue somewhere in that history does not mean it is safe to bring it upon ourselves with our own actions. Giant meteor or nuke, you don't want to be standing next to it when it impacts.
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  10. You have a small typo in the Intermediate summary. The second sentence reads "Therefore human emissions upset the natural balance, rising ...". It should say "raising".
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  11. #7. HumanityRules, 20 million years ago sea level was about 90 m higher, Miller, 1996, and 100 million years ago it was about 145 m higher than it is today Müller 2008. That's what so special: global sea levels are intimately related to CO2 levels. Do you want sea levels like that in the near future ?
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  12. This is how the argument gets (ab)used by deniers 1) 29 gigatons is safely in the margin of error (given our measurement ability) of the natural carbon cycle (771 gigatons) 2)Regarding actions: The US is responsible for 25% of the global human induced CO2 emissions. Official plans call for very minor reductions, but even if you use 20% from a likely baseline, 20% of 25% of 2ppm (annual increase in CO2) is 0.1ppm and virtually unmeasurable. I myself come from the school of thought that says step one is to stop digging - any help for responding to the sophism I outline above?
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  13. #12: "29 gigatons is safely in the margin of error (given our measurement ability) of the natural carbon cycle (771 gigatons)" If, as stated in the post, the larger amount is "moving through the carbon cycle each year", then it would seem to have little to do with the 50+ year trend. Atmospheric CO2 graphs display an annual oscillation superimposed on a long-period rise. The peak-to-trough excursion of the annual cycle (up to 15ppm/year in some places) is distinct from the 2ppm trend. A related question -- is it possible to quantify how much of the 'natural cycle' is due to wild growth vs. how much is due to agriculture? Would that be a valid part of the response to the argument that 'human influence is too small to be detected'?
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  14. muoncounter at 13:33 PM, the peak to trough variation in the annual cycle is far greater in some places, as high as 50ppm as shown in Mechanisms for synoptic variations of atmospheric CO2 in North America, South America and Europe so there is far greater capacity to sequester CO2 than is fully realised. If the growing seasons extend then perhaps more of that capacity will be utilised. As virtually all enrichment trials indicate, plant growth under present conditions is far from optimum, low CO2 levels being the factor being focused on, with CO2 enrichment being a long established practice in many commercial intensive plant production systems.
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  15. #14: "there is far greater capacity to sequester CO2 than is fully realised. " If, by sequester, you mean temporarily house within the plant growth for half of the annual cycle. Take those cycles out and you're still left with an uptrend -- which is not, as far as I can see, part of the annual cycle. What is left that is also increasing from year to year and is also the right multiple of the annual atmospheric increase?
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  16. Sorry to burst formatting error, please discard my post
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    Moderator Response: I think I fixed the formatting errors...

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