Episode 247. What Is The Carbon Cycle?

This is The ChangeUnderground for the week ending 1st of March 2021.

I’m your host, Jon Moore

Decarbonise the Air, Recarbonise the Soil!

From the NASA Earth Observatory site:


Through a series of chemical reactions and tectonic activity, carbon takes between 100-200 million years to move between rocks, soil, ocean, and atmosphere in the slow carbon cycle.

End Quote

This sort of thing has been going on for, well, since the earth started to form and cool. This is not the cycle we are messing with as humans but it is worth knowing that it happens and that it acts as a thermostat for the planet. A base level of temperature is a good way to think about it.

Remember this is the Slow Carbon Cycle. In this cycle rain forms compounds with CO2 and falls to earth as a weak acid. This dissolves rocks, slowly, which flow into the ocean where it forms calcium carbonate in the form of shells and plankton and so on. These die, eventually, fall to the bottom of the oceans, and are driven through plate tectonics into the liquid part of the earth where it wanders around until it is ejected as CO2 through volcanoes and the cycle continues. It appears this cycle takes between 100 and 200 million years to complete.

The other cycle, not unsurprisingly, is the Fast Carbon Cycle. And it is considerably faster, about a human lifetime. It’s the one we are probably more familiar with. Carbon is, on this planet, the element of life. Carbon bonds are pretty much everywhere in living things. The more complex of these store much energy in their bonds, releasing this energy when broken. There are therefore, great food sources for living things that are themselves comprised of these complex molecules. DNA itself is built around two chains of complex carbon chains. Phytoplankton at sea and plants on land and at sea represent the major components of the Fast Cycle. They are where the carbon is lodged. 

The key activity in kicking off the Fast Carbon Cycle is photosynthesis. During this process, CO2 and H2O combine with energy, sunlight to create sugar CH2O and O2. In the simplest of terms the carbon moves from the carbon dioxide and is joined to the water. The sugars are used to build all the other things in the living world. We are learning how the flow of these sugars and other molecules are mediated by the soil biota but let’s stick with the carbon for the moment.

As in the Slow Cycle the Fast Cycle starts as CO2 and ends as CO2. In the Fast Cycle there are but four ways the C held in the CH2O can be released to reform as CO2.

  1. Plants use the sugar for their own metabolic needs
  2. Animals eat the plants/phytoplanktons
  3. Plants are consumed by bacteria/fungi at the end of their lifecycle
  4. Fire

A quick look at these would point to some implications for our current warming predicament. Points 3 and 4 Plants at the end of the life cycle and fire. We’ll come back to those later.

The Fast Cycle varies over the year. In deciduous forests, large amounts of carbon are released with leaf drop and little is taken up as trees fall dormant. This is counterbalanced by massive growth spurts in Spring so it’s an equalising system. 

Somewhere between 1,000 million and 100,000 million tonnes of carbon are cycled through the fast cycle. 

As the slow and the fast cycles interact over time we experience periods of glaciation, Ice Ages, and periods of interglaciation. From about 10 to 12,000 years ago the planet came out of a glacial period, the Pleistocene and entered the Holocene, an interglacial period. All very normal.

Slowly but increasingly up to 1950 humans added more CO2 to the atmosphere each year until in 1950 we were adding about 2,000 million tons per annum. Since then the figure has risen to about 8,000 million tons. At the same time we have been clearing more forests in Australia, the Amazon, tropical Asia and Africa to replace them with pastures and cropping. The difference in the total biomass alone should raise questions like: Where did all that carbon go? Does that matter? 

Second question first, Yes and first question second, into the atmosphere and oceans. 

Now back to points 3 and 4. The end of life and fires. The figures are not fully calculated yet but the biomass destroyed in the wildfires of 2019/2020 in Australia is not yet fully replaced, that is, has not yet drawn down the CO2 that was released.

We can see from simple activities like land clearing, biomass volume reduction in other words and wildfires, humans can and have disrupted the fast cycle. If we toss in, as we must, the volume of CO2 released through the burning of coal, oil and natural gas, the predicament we find ourselves in be     comes more obvious. 

Given that this extra CO2 makes the planet a touch warmer and then a bit more warmerand then even more, and that wildfires release even more CO2 to bump the temperatures even higher, it becomes obvious we are feeding a constantly growing beast. Think wildfires in Siberia instead of permafrost and the problem is clear. 

What’s to be done?

This is where I fall into a deep depression, some days. I am predominantly an optimist but there are days when I feel helpless in the face of the natural forces arrayed before us. Toss in the brain dead political situation here in Australia and the US and in Brazil and in, well pick your nation here, and it’s a wonder anyone gets out of bed.

But we do. We garden, we grow, we build organic matter, we probably don’t look too closely at the numbers for in that direction lies despair. 

More importantly for me I come back to the last four lines of poem by the Kerry poet Brendan Kennelly entitled Begin and I will quote these lines now:

Though we live in a world that dreams of ending 

that always seems about to give in 

something that will not acknowledge conclusion 

insists that we forever begin

These words give me hope, they haunt me and comfort me and given the data, a little bit of poetry might just be what we need right now.

Thank you all for listening and I’ll be back next week!



The ChangeUnderground Academy No-Dig Gardening Course:



email: jon@worldorganicnews.com


The Carbon Cycle


Leave a Reply

Your email address will not be published. Required fields are marked *