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At a glance – How do human CO2 emissions compare to natural CO2 emissions?

At a glance – How do human CO2 emissions compare to natural CO2 emissions?

Posted on 26 September 2023 by John Mason, BaerbelW

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added “At a glance” section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a “bump” for our ask. This week features “How do human CO2 emissions compare to natural CO2 emissions?“. More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

Fact Myth CO2

At a glance

Have you heard of Earth’s carbon cycle? Not everyone has, but it’s one of the most important features of our planet. It involves the movement of carbon through life, the air, the oceans, soils and rocks. The carbon cycle is constant, eternal and everywhere. It’s also a vital temperature control-mechanism.

There are two key components to the carbon cycle, a fast part and a slow part. The fast carbon cycle involves the seasonal movement of carbon through the air, life and shallow waters. A significant amount of carbon dioxide is exchanged between the atmosphere and oceans every year, but the fast carbon cycle’s most important participants are plants. Many plants take in carbon dioxide for photosynthesis in the growing season then return the CO2 back to the atmosphere during the winter, when foliage dies and decays.

As a consequence of the role of plants, a very noticeable feature of the fast carbon cycle is that it causes carbon dioxide levels to fluctuate in a regular, seasonal pattern. It’s like a heartbeat, the pulse of the Northern Hemisphere’s growing season. That’s where more of Earth’s land surface is situated. In the Northern Hemisphere winter, many plants are either dead or dormant and carbon dioxide levels rise. The reverse happens in the spring and early summer when the growing season is at its height.

In this way, despite the vast amounts of carbon involved, a kind of seasonal balance is preserved. Those seasonal plant-based peaks and troughs and air-water exchanges cancel each other out. Well, that used to be the case. Due to that seasonal balance, annual changes in carbon dioxide levels form regular, symmetric wobbles on an upward slope. The upward slope represents our addition of carbon dioxide to the atmosphere through fossil fuel burning.

Fossil fuels are geological carbon reservoirs. As such, they are part of the slow carbon cycle. The slow carbon cycle takes place over geological time-scales so normally it’s not noticeable on a day to day basis. In the slow carbon cycle, carbon is released by geological processes such as volcanism. It is also locked up long-term in reservoirs like the oceans, limestone, coal, oil or gas. For example, the “37,400 billion tons of ‘suspended’ carbon” referred to in the myth at the top of this page is in fact dissolved inorganic carbon in the deep oceans.

Globally, the mixing of the deep ocean waters and those nearer the surface is a slow business. It takes place over many thousands of years. As a consequence, 75% of all carbon attributable to the emissions of the industrial age remains in the upper 1,000 m of the oceans. It has not had time to mix yet.

Fluctuations in Earth’s slow carbon cycle are the regulating mechanism of the greenhouse effect. The slow carbon cycle therefore acts as a planetary thermostat, a control-knob that regulates global temperatures over millions of years.

Now, imagine the following scenario. You come across an unfamiliar item of machinery that performs a vital role, for example life support in a hospital. It has a complicated control panel of knobs and dials. Do you think it is a good idea to start randomly turning the knobs this way and that, to see what happens? No. Yet that is precisely what we are doing by burning Earth’s fossil fuel reserves. We are tinkering with the controls of Earth’s slow carbon cycle, mostly without knowing what the knobs do – and that is despite over a century of science informing us precisely what will happen.

Please use this form to provide feedback about this new “At a glance” section. Read a more technical version below or dig deeper via the tabs above

In case you’d like to explore more of our recently updated rebuttals, here are the links to all of them:

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