ENVIRONMENTAL CENTS: The Carbon Cycle

We're producing more carbon than the earth can absorb. What are the sources and "sinks" that make up the carbon cycle? And what can we do to help? Bruce Saller explains.

By Bruce Saller
COLUMNIST

Photo by Chris LeBoutillier on Unsplash

The earth has a carbon cycle where carbon is added to the atmosphere by natural sources and removed by natural sinks. 

Natural sources include outgassing from the ocean, volcanos, decomposing plants, fires, and animal respiration. Natural sinks include forests, soil and oceans.  Approximately 100 billion metric tons (100 GigiTons or GTs) of carbon move through this cycle annually. (This is the same amount of carbon in 350 GTs of carbon dioxide.)

Until the Industrial Revolution (circa 1750), the small amount of carbon produced by humans was able to be absorbed in the natural carbon cycle. Around 1920, humans were adding about 1 GT of carbon to the atmosphere per year; by 2020 we were adding 10 GTs. The natural carbon cycle has only been able to absorb about 55% of this carbon, with the remainder entering the atmosphere.

Humans are also impacting the natural carbon cycle. Deforestation and other land-use changes are reducing the amount of carbon the land can absorb by an average of 1.2 GT per year. The warming climate is also increasing natural carbon release. Wildfires are burning more acres due to the hotter and dryer weather. Permafrost is melting in the Artic allowing organic matter to break down, releasing carbon into the atmosphere. So in addition to adding carbon to the atmosphere, we are also reducing the amount of carbon that the natural cycle can remove.

So how long do greenhouse gases stay in the atmosphere? Methane (natural gas) makes up 16% of global greenhouse gas emissions but traps 28 times as much heat as carbon dioxide. Methane gas reacts with oxygen and turns into carbon dioxide and water within a few years. 

Carbon dioxide is the most prevalent greenhouse gas making up 76% of emissions.  Unfortunately, carbon dioxide does not react with other molecules and takes thousands of years to be absorbed by the ocean, plants or the land. 

Nitrous oxide comprises 6% of emissions, but is 300 times as potent as carbon dioxide and stays in the atmosphere for over a century until it is absorbed. Most nitrous oxide emissions come from fertilizer and cows.

So, what can we do to help?

1. Reduce use of natural gas.

2. Reduce use of nitrogen-based fertilizer.

3. Plant trees and shrubs.

4. Use electric lawn and garden equipment.

5. Consider purchasing an electric vehicle.

6. Consider installing solar panels.

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