How Much Carbon?

September 21, 2017 by Denis Pombriant

We hear a lot about carbon dioxide in the atmosphere and many people disagree about whether atmospheric carbon can really affect climate. We don’t very often discuss it in hard numbers though. The most often used measurement of atmospheric carbon today is 400 parts per million (ppm) and rising which means that out of a million air molecules only 400, a very small number, are carbon dioxide but don’t be lulled by this simple statement.

Currently the Department of Energy’s Energy Information Administration or EIA estimates that there are between 5 trillion and 6 trillion tons of carbon dioxide in the atmosphere, most of it placed there by human activity. The same body says that we’re pumping between 35 billion and 45 billion tons of carbon dioxide into the air each year adding to the problem. So it’s only parts per million but it adds up.

Efforts to curb carbon emissions can be confusing because they imply that by reducing the rate by which we add carbon to the atmosphere we can solve the problem. But there’s already too much carbon in the air so slowing the rate of addition isn’t going to be enough by itself to solve the problem.

At the same time we reduce emissions we need to do two other things. We need to find non-polluting substitutes for the energy we forego from burning fossil fuels, and we need to find efficient ways to remove carbon from the air that don’t use energy from burning fossil fuels because you can’t get ahead of the problem if you make more pollution to solve the pollution problem.

Experts like to point to the level of CO2 in the atmosphere at the beginning of the Industrial Revolution for two good reasons. First, they estimate the concentration of CO2 in the air was 280 ppm at that point and the Industrial Revolution was the time when humanity began using fossil fuels in significant and growing quantities. The conclusion some people leap to is that 280 ppm is safe.

But the concentration of carbon in the air has fluctuated over the course of earth’s history so the question of safety has to be examined with greater nuance. Safe for what? After all, throughout the 20th century CO2 levels were higher than 280 ppm and for much of that time climate fluctuations were tolerable. However, that’s the point of climate change; when climate changes regions that are hospitable to growing food, for instance, can become too warm or too dry for farming. Other regions might become too wet from the same phenomenon and excessive rainfall can be just as bad for plant growth as too little.

So climate change can have a big impact on food production. In pre-history, changing climate mattered less than it does today. When one area became too dry or too wet, some individuals died as a result while others moved to more hospitable areas. These ecological changes become evolutionary challenges that drive evolution. You can see this kind of challenge all over the world as dry seasons alternate with wet seasons and large herds of land animals or flocks of birds migrate.

But back to green plants. They have a natural capacity for removing carbon dioxide from the air; they split water molecules using energy from sunlight and combine hydrogen atoms with carbon dioxide to make simple sugars and they also release oxygen into the air. Then plants combine simple sugars into products like wood, fibers, and food. It’s a complete cycle and very importantly, when carbon is taken out of the atmosphere it doesn’t add to climate change.

Each year green plants on the earth produce between 100 and 115 billion tons of biomass using nothing but sunlight, carbon from the atmosphere, water, and a few trace elements. That’s photosynthesis and it happens on land at farms as well as your lawn and every place in between. It also works the same way in the ocean.

If we could encourage more photosynthesis on earth then natural systems could do the work of removing carbon from the air and reducing the impact of climate change. Increasing the amount of photosynthesis on earth is a big challenge. In subsequent posts we’ll answer questions like, where would the plants grow? How would they get nutrients and water? And we’ll look at some other benefits of using natural systems to do what they already do best.

When you consider the need for an adequate supply of CO2 for food production and the need to keep it out of the air, the inescapable conclusion is that some of amount of carbon should be warehoused in organic matter, which could satisfy both conditions. If we can grow more green plants they can capture more carbon keeping it out of the air; if those plants happen to produce food for human consumption, so much the better. Of course carbon I this way will not stay out of the atmosphere for long. The natural carbon cycle moves carbon from the atmosphere to plants and eventually to plant consumers rather quickly. So an approach that uses photosynthesis hast to, essentially, never stop, which is fine because there’s a constant need for food.

Over the last few hundred years, the human population on the planet has exploded so that it’s not possible for any large group of people to lead a nomadic existence as our ancestors did. The land has been claimed and some parts are used for growing food while others may be used for cities or for dwellings and other human activities.

The tough part of climate change, given our population, is that it threatens to make farm land un-farmable moving growing regions and disrupting civilization in the process.

Another difficulty in trying to figure out how much atmospheric carbon we can tolerate has to do with how green plants turn inorganic CO2 into the foods we eat. Carbon moves in a continuous cycle from inorganic CO2 to green plants that turn it into organic material, some of which is food while some is simply plant material like leaves, branches, roots, etc. Call it all biomass. At some point animals might eat the food to satisfy their energy needs and in the process the food is converted back into CO2 and water.

Today we also get a lot of carbon from fossil fuels that were formed millions of years ago and sequestered from the rest of the world. This process is still ongoing but it can take millions of years.

One possible solution to the climate problem might be to treat the problem as a chronic need rather than an acute one. An acute need is an emergency that has to be solved at once without delay. On the other hand a chronic problem is always there and requires management.



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