Carbon’s dangerous dance with oxygen

All life on this planet is based on carbon; every plant, animal and micro-organism is built from this element. Humans are 19 per cent carbon, trees are 50 per cent and peat soils can contain 18-60 per cent carbon.

We eat carbon in our food, breathe it in and out, burn it for energy and heat and build things from it, it truly is a wondrous material. Carbon is locked up in the bodies of living organisms or in the remains of undecayed dead organisms, these are carbon stores. Fossil fuels are the biggest carbon stores on the planet. Coal, oil, gas and peat are the carbon-rich remains of vast ecosystems accumulated over millions of years.

Carbon loves oxygen, and when carbon is introduced to oxygen through burning, respiration or decomposition the climate-warming molecule carbon dioxide is the product of their union. Eliminating our use of fossil fuels is the most important lever we have available to us to reduce the amount of carbon dioxide in the atmosphere. The commitments made by world governments to achieve net-zero carbon emissions by 2050 demonstrate that the value of fossil fuels to humanity must transition to a carbon store rather than a fuel.

Carbon is also stored in the Earth’s contemporary ecosystems, which if released would make climate change far worse. Fully functional ecosystems can be in carbon equilibrium, with the amount of carbon released equal to the amount of carbon locked away in living and undecayed material.

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Indeed, fully functional peat bogs, undisturbed grasslands and young forests can remove more carbon dioxide from the air than is being released and are therefore actively sequestering carbon. The reality is though that many natural ecosystems as well as agricultural land in Ireland, and globally, emit greenhouse gases, including carbon dioxide.

Humans have a big influence on how carbon moves through ecosystems and how often it encounters its old friend oxygen. Carbon dioxide is produced from carbon stored in plants and soils when they are burned, harvested and decomposed. In wet peat soils water squeezes into the natural pores and holes in soil, protecting the carbon, but when these soils are drained oxygen moves into the pores, where it reacts with carbon, releasing carbon dioxide.

Ploughing brings carbon buried in low oxygen conditions to the surface where it reacts with the abundant oxygen. Altogether, human land use is responsible for about a quarter of human caused global greenhouse gas emissions.

Many of the practices we previously considered as ‘land improvement, such as clearing woody vegetation, drainage, ploughing and fertilisation, cause the degradation of carbon stores and prevent that land from removing carbon dioxide from the atmosphere

Habitat restoration to repair damaged ecosystems and return them to healthy functioning is a nature-based solution to prevent further carbon loss and ideally turn the recovering ecosystems into carbon sinks where they sequester more carbon than they release.

Wetting soils and returning their hydrological integrity can help to delay the decomposition of carbon, which is how peat bogs build up such large quantities of carbon over decades, centuries and millennia. Rewetting peat soils that were previously drained can help to prevent the release of the carbon that remains and re-establish carbon capture processes.

While wet peat soils emit methane, another climate warming gas produced from the decomposition of living material in the absence of oxygen, a fully functional peat soil ecosystem will have a net gain of carbon where greenhouse gas emissions are balanced by carbon sequestered.

The release of nitrous oxide is higher in wet soils, another very potent greenhouse gas, particularly where those soils are over-fertilised. Limiting the use of synthetic fertilisers, using protected forms of nitrogen fertilisers and limiting slurry spreading can all help with management of nitrous oxide emissions.

When land is changed from one use to another the carbon consequences can be devastating. Many of the practices we previously considered as “land improvement”, such as clearing woody vegetation, drainage, ploughing and fertilisation, cause the degradation of carbon stores and prevent that land from removing carbon dioxide from the atmosphere.

We must prevent deforestation, find ways of farming that support a positive carbon balance, plant forests on appropriate soils, ensure long-term use of harvested wood products and find ways to restore natural ecosystems so that they sequester carbon while supporting nature. We need to protect our carbon stores from a dangerous dance with oxygen.

Yvonne Buckley is an ecologist, Irish Research Council laureate and professor of zoology at Trinity College Dublin