THE CARBON CYCLE

What is The Carbon Cycle and why is it so important?

Carbon is in everything

So what is carbon? Carbon is an extremely abundant element found in many different forms in, on, and above Planet Earth. Carbon is found in the atmosphere in the form of carbon dioxide and methane gas. Carbon is also a main component of plant and animal tissue. All of the food we eat contains carbon, and as a result, our bodies contain a lot of carbon as well. Carbon is found in the oceans and in aquatic organisms. Carbon is also found in many mineral deposits, such as limestone and marble.

We hear about carbon in discussions and news reports about climate change, emissions, greenhouse gases, and clean energy. But what role does carbon have to play in all this? Among the many other carbon-based substances found around the planet, carbon is a major component of fossil fuels. When these fuels are burnt to heat our homes or to power our vehicles, carbon is released into the atmosphere in the form of greenhouse gases, which trap heat within our atmosphere.

 

When viewed within the narrow context of fossil fuels and greenhouse gases, carbon itself can seem like a problem. However, carbon is everywhere, constantly transforming from one substance into another. This movement and transformation happens in a series of natural processes that are collectively known as the Carbon Cycle. Some of these processes are slow, taking place over the course of millions of years. Others, however, are rapid processes, in which carbon can assume multiple forms over the course of a single year.

 

Through a series of chemical reactions, carbon is slowly but constantly transforming from carbon dioxide in the atmosphere into mineral deposits on the ocean floor, with some cycling back into the atmosphere via plate tectonics and volcanism. These processes began billions of years ago, when the concentration of carbon dioxide in the atmosphere was extremely high due to persistent volcanic activity. At this point, Planet Earth was very hot, as carbon dioxide, a greenhouse gas, traps heat in the atmosphere in what is known as the greenhouse effect. Over millions of years, carbon dioxide in the atmosphere dissolved in rain water and stabilized as oceanic mineral deposits. This series of slow processes, known today as the geological carbon cycle, was able to cool the atmosphere enough to allow life to evolve.

The Evolution of the Carbon Cycle

As life on planet earth evolved, so did the carbon cycle. In the presence of a carbon-dioxide-rich atmosphere, some of earth’s earliest life forms - the cyanobacteria - evolved to use energy from the sun. In a process called photosynthesis, these bacteria used solar energy to combine atmospheric carbon dioxide and water to form organic compounds and oxygen. This key process effectively kicked the carbon cycle into overdrive, facilitating the movement of carbon out of the atmosphere at a much faster rate.

 

Plants use photosynthesis to produce carbon-based compounds such as carbohydrates, fats, and proteins, which they use to grow. As animals consume these plants, they incorporate these carbon compounds into their bodies, consuming the carbohydrates and fats as energy, and using proteins to build muscle, and eliminating carbon-rich waste in the process. As plants grow, they continually eliminate a portion of these carbon compounds through their roots, creating a liquid carbon pathway between the atmosphere and the soil. As plants and animals complete their life cycle, they deposit carbon-rich organic material on the earth’s surface. This carbon-based material that ends up on or within the soil is then consumed by insects, bacteria, and other microorganisms. Eventually, carbon ends up in stable form within the soil, known as humus, comprising an important part of soil organic matter.

 

Soil organic matter combines with mineral deposits caused by weathering, creating organic soils. In wetlands and other aquatic environments, plant and animal residue break down slowly in the absence of oxygen, creating underwater deposits of stable organic material called peat. Hundreds of millions of years ago, some of these stable deposits of organic matter were buried via earthquakes and other seismic activity. These buried deposits of organic matter, being exposed to heat and pressure over the course of millions of years, eventually formed the very stable, energy dense carbon compounds that we know as fossil fuels.

Over the past 3 billion years, the processes of photosynthesis and chemical weathering fixed large quantities of atmospheric carbon dioxide into plant, animal, and microbial biomass, organic soil and wetland residue, and oceanic mineral deposits. Other processes associated with the carbon cycle, such as respiration and oxidation, continued to cycle carbon dioxide back into the atmosphere, but the vast majority of carbon remained fixed within these sinks, remaining stable for thousands, to hundreds of millions of years. As a result, global temperatures continued to decrease, until the concentration of carbon dioxide in the atmosphere eventually stabilized, with the terrestrial biosphere (plants, animals, and microbes) being the primary carbon sink.

 

In the absence of large-scale human interference, the global carbon balance remained relatively stable up until the beginning of the Industrial Revolution, which brought on the consumption of large amounts of carbon-based fuels to power the production of textiles, iron, chemicals, and other materials. The burning of these fuels released large quantities of carbon dioxide into the atmosphere, which began to throw off the natural carbon balance.

 

Changes in land-use related to agriculture and deforestation exacerbated the issue, not only by facilitating the release of carbon dioxide back into the atmosphere, but also by limiting the ability of the terrestrial biosphere to pull carbon out of the atmosphere via photosynthesis. According to the Global Carbon Project, since the beginning of the Industrial Revolution, human activity has releases 2,000 gigatons (2 trillion metric tons) of carbon dioxide into the atmosphere, increasing the carbon dioxide content in the atmosphere by 40% in only 250 years. Human activity has, in an extremely short period of time, effectively reversed the natural flux of carbon, adding more to the atmosphere than is pulled out via natural processes.

The most direct measure to limit the increase of carbon dioxide in the atmosphere is to reduce the consumption of fossil fuels. However, since the terrestrial biosphere is a carbon sink, harnessing the power of nature to pull more carbon dioxide out of the atmosphere is also essential to addressing climate change. The IPCC’s fifth assessment on climate change highlights a variety of agricultural management practices with potential to decrease agriculture-related emissions and to increase rates of carbon sequestration within plants and soils. At Hudson Carbon, we are dedicated to developing a set of regenerative agricultural management tools that will allow farmers and land managers to play a part in reversing the effects of climate change while continuing to feed a growing population.

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