What is biogenic carbon?

By Mattias Jönsson

28 September, 2021

Biogenic Carbon

Climate change has become of greater focus to us over the past few years.  The Earth is warming up due to a blanket of ‘greenhouse gases’ in the atmosphere preventing heat from escaping.  There are many greenhouse gases including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).  We calculate the total greenhouse gas emissions in terms of carbon dioxide equivalents and therefore we sometimes refer to the causes of climate change as just ‘carbon’ or ‘carbon footprint’.

There are two sources of CO2: biomass (biogenic carbon) and fossil fuels (fossil carbon).  They both store CO2 and release it during decomposition.  In this article we will explore what biogenic carbon is and how it differs from fossil carbon.

What is Biogenic Carbon?

Biogenic carbon is the CO2 absorbed from the atmosphere when plants grow.  It is then released when the plants are eaten, burnt or composted.  This is the natural carbon cycle and over the lifetime of a plant there is a net zero change in the CO2 in the atmosphere.  This may also be referred to as ‘carbon neutral’.

However, humans can take plant material and use it to produce energy, whilst releasing the biogenic CO2.  For example:

  • Collecting biogas (methane) and burning it.  Biogas can be collected from plant waste decomposing in landfills, sewer water treatment or animal manure.
  • Burning of plant materials in municipal waste at incinerators which produce electrical and thermal energy.
  • Burning wood on a fire for heat.

What is the difference between CO2 Produced By Biogenic Carbon and Fossil Fuels?

It is easy to get confused between the carbon dioxide released by biogenic and fossil processes.  Indeed, to get the same amount of energy more CO2 is released from burning biogenic sources than fossil such as coal.  And fossil fuels are made from plants and animals which died millions of years ago, so surely they are the same thing?

The difference here is time.  Burning fossil fuels releases carbon which has been locked up underground for millions of years.  This fossil carbon increases the net carbon in the atmosphere over our lifetimes.  Burning plants releases carbon which was absorbed during their growth phase, so a net zero change to the atmospheric carbon over our lifetimes.

Climate change is calculated on a 100 year time frame and for this very reason that plants are net zero.  Therefore when we look at CO2 emissions we separate those from biogenic sources and from fossil sources.

In summary, biogenic carbon is carbon stored and released by plants as part of the natural carbon cycle.  It is important to report it separately to fossil carbon, due to the different absorption and emission time scales. 

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