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Human CO2: Peddling Myths About The Carbon Cycle

August 31, 2010

Climate change sceptics argue that because human emissions of CO2 are very small compared to the annual cycle of natural CO2, we cannot be changing the climate. To maintain this fiction, it is necessary to ignore the build-up of CO2 which we know comes from burning fossil fuel.

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 in the atmosphere has increased 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.

Footnote: this post was written for SkepticalScience as part of an ongoing project to add ‘basic’ rebuttals of common climate change denial arguments. References for all statements can be found in the intermediate discussion Human CO2 are a tiny percentage of CO2 emissions.

3 Comments leave one →
  1. simon permalink
    September 1, 2010 2:24 am

    The sceptics also ignore the fact that humans have cleared away the natural carbon sinks on land over the last 8000 years. 75% of forests 80% of swamps, its got to have an effect.
    Its not as if natural co2 emissions had somewhere to go, co2 from before the IR began to build up. The only carbon sink left alone was the sea but even now that is not doing the job it once was.
    Unfortunatly we can only watch the worse happen. The problem is that there is no where left for the co2 to go so even if we cut emissions the atmospheric content will continue to grow.
    Its a lost battle. We do this kind of thing as humans, we fight for lost causes and never seem to give in. We thought we won the war against nature, we built our all weather habitats put food on the table for generations, but nothing lasts for ever.

  2. Graham Wayne permalink*
    September 1, 2010 6:37 am

    Hi Simon. You are quite right – even now the rainforests are still being hacked down for short-term gain, like a cancer eating away at the Earth’s lungs. As for the oceans, the ability of water to absorb CO2 is a function of temperature. The warmer the seas get, the less CO2 they can absorb. On top of this slowing down of the natural ‘sink’ capacity, the oceans expel CO2 already absorbed as the water heats up, and of course the extra CO2 it is taking in is changing the pH of the water, making it more acidic. This could have profound negative effects on the food chain, considering that billions of people depend on fish for their primary nutrients.

  3. JeffM permalink
    September 2, 2010 4:01 am

    With about $400 million in venture capital, Bloom Energy has developed a fuel cell technology that was recently unvailed. Unless big energy companies find a way to shut down Bloom’s fuel cells, we may very well have the Holy Grail of affordable, clean energy at hand.

    The big question will be, if this new fuel cell technology proves to be as claimed, what will be its effect on the global economy? How will oil and coal interests react, and what obstacles will government build to thwart the actual replacement for carbon fuels? Thus far, after claiming that carbon fuels are a threat to humanity, government has yet to embark on a “Manhattan Project” to fund the R&D to find an affordable energy source to replace carbon fuels. Government has only focused on subsidizing ($billions) for part time energy technologies (wind, solar, biofuels) that will always require traditional carbon fuels to back them up.

    Could it be that government doesn’t actually WANT to do away with carbon fuels? If so, how can Bloom’s fuel cells have a chance in the market place?

    If carbon fuels are really the threat that government says they are, shouldn’t government want to put its money into finding a replacement for carbon fuels?

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