What is our greatest terrestial carbon reservoir?

For as long as I can remember, the world has been obsessed with the protection of rain forests.  As the threat of global climate change becomes reality, we are now obsessed with things like pollution levels, carbon capture and our own individual carbon footprints.

The other day I was told by a lecturer that an increase in terrestrial carbon levels (that stored in the soil and vegetation worldwide) of 15% would reverse the impact of fossil fuel pollution that has occurred since the industrial revolution.




Now, I know there are those climate skeptics out there who still have their heads buried deep in the sand, but the fact is this: the earth's climate is changing at rates far in excess of those previously experienced by the planet.

Sure, there are natural cycles and events which contribute to changing the climate in the normal course of things.  But what is happening now is NOT normal.

It is human induced climate change.  Or, if it makes you feel better, accelerated climate change.

When I say that, I am taking into account all of the actions we have taken which have led us to this point.  Not just pollution levels since the industrial revolution, but also the mass clearing of land to provide more living space agricultural space to house and feed our growing population.

Every time we plough or clear an area of land, we are releasing carbon into the atmosphere.  This happens through the process of oxidation, where the organic carbons are exposed to oxygen and join to form CO2.

It is estimated that, on clearing an area, 100% of the carbon from the vegetation and approximately 25% from the soil is lost.  As the soil is then turned over, worked and / or cultivated, further carbon is lost to the atmosphere.

Roughly, 7.5% of the total terrestrial carbon stores are held in the vegetation of our forests, with the tropical rainforests we were all so concerned about back in the 80s holding onto the majority of that.  Around 4% is held in the vegetation of our grasslands.  For vegetation that is part of agricultural ecosystems, that's about 2.7%.  Less than 1% is held in the vegetation of lands that are considered barre, wetlands and human settlements.

The remaining 85% of the terrestrial carbon stores are in our soil.  85%.

Of this, about 27% is held in the soil of our forests and 33% in the soil of our grasslands.  15% is held in the soil of agricultural ecosystems and the remainder in barren lands, wetlands and human settlements.

These percentages are actually the lowest estimates available, and nor do they take into account the soil carbon data for Greenland or Antartica. 

So what does that mean in real terms?  It means that if we want to not just slow climate change down, but actually have a shot at reversing the trend, we need to be concentrating on rebuilding and increasing the organic carbon reserves in our soil.

For you at home and farmers alike, this means getting as much organic matter back into the soil as possible.  Composting, biochar, using molasses, feeding the soil biota, mulching with organic matter, reducing tillage, digging in crop stubble instead of burning or selling it on, using green manures and digging those in, never leaving a field or garden bed bare where oxidation can increase, stop selling your animal manures and compost them on site then use them on your own land, feeding the microbes...

organic matter -> humus = carbon capture in your soil

What are you waiting for? :)

Sources:

• PAGE report, Grassland Ecosystems, December 2000, authors Robin White, Siobhan Murray and Mark Rohweder of the World Resources Institute.
• The Role of Terrestrial Carbon in the Climate Change Solution, December 2009, produced by the Terrestrial Carbon Group Project