The Carbon Cycle? Well, carbon has become a global threat to humanity. Historically, carbon has been doing just fine supporting life on Earth and regulating its temperature, like a thermostat. And we’re also made of carbon, eat carbon, and build our communities with carbon. It sounds pretty contradictory, doesn’t it?
Then we came along and started burning lots of fossil fuels worldwide, increasing the amount of greenhouse gases, primarily carbon dioxide (CO2), in the atmosphere to a threat-to-humanity level. So, how did we end up here? And how does it all work? Welcome to Biology 101 with Deedster!
As the fourth most abundant element in the universe, carbon is all around. And it’s constantly on the move in what’s known as the carbon cycle. To make things easier, we can divide it into two different cycles. Let’s start by taking it slow…
The Slow Carbon Cycle
Most of the carbon on Earth, some 65 500 billion tonnes, is stored in the lithosphere (deep underground in rocks). So how does it get into the atmosphere? Well, without human aid (we’ll get to that later), it occurs through volcanic eruptions. As heat and pressure build up in the ground, carbon transforms into gases such as CO2 released into the atmosphere during a volcanic eruption.
Once in the atmosphere, the journey back to the lithosphere begins with rain. The carbon in the atmosphere combines with water in the air to form carbonic acid, which dissolves carbon-containing rocks and releases various ions (atoms) that contain carbon.
These ions are then carried to the ocean by rivers and consumed by marine organisms like plankton and corals. When these creatures die, they sink to the ocean floor and take the carbon with them, forming sediment. Over time, the carbon slowly returns to the lithosphere as rocks, storing the carbon. Sometimes, when the layer of sediment gets subjected to intense heat and pressure deep underground, it’s transformed into fossil fuels such as coal, oil, and natural gas instead.
And now, some 100-200 million years later (you get why they call it the slow carbon cycle now, huh?), we’ve come full circle as the carbon has moved from rocks to the atmosphere and ocean, and then back to stones.
And this cycle is Earth’s thermostat, which keeps too much carbon from entering the atmosphere (where it heats the planet) and keeps too much carbon from being stored in the lithosphere (which cools down the Earth).
The Fast Carbon Cycle
Ready to speed it up a notch? While it takes carbon 100-200 million years to move through the slow cycle, we can measure the fast cycle in lifespans. And that’s simply because it concerns carbon movement through Earth’s biosphere (its ecosystems and living creatures).
Carbon is essential in biology as it combines with other elements into complex molecules, forming long carbon chains and rings that are the basis of living cells. One example is DNA, which is built around a carbon chain. These carbon chains also contain a lot of energy, which is released when the chain breaks apart. And all living creatures need energy, making carbon an excellent fuel for living organisms.
The most important living organisms in the fast carbon cycle are plants and phytoplankton (microscopic marine plants). They absorb CO2 from the atmosphere and combine it with water to form sugars, such as glucose and oxygen, through photosynthesis. The carbon then returns to the atmosphere in different ways. The plant either decays, gets eaten by animals (including humans), or gets consumed by fire. No matter how it happens, the plants release water, CO2, and energy.
The Unnatural Carbon Cycle?
That’s the natural circle of life for carbon. So what happens if a living organism, say humans, suddenly begins extracting vast amounts of carbon from the lithosphere (as fossil fuels) and burns it? Well, energy is of course released, which is helpful to fuel our growing civilisations. But also, and somewhat problematically as we have realised, it also emits CO2 into the atmosphere.
Greenhouse gases, such as CO2 regulate Earth’s temperature since they can absorb a lot of energy, including the infrared energy (heat) emitted from the sun. This prevents Earth from becoming a frozen and desolate planet like our neighbour Mars. On the other hand, too much greenhouse gas would turn Earth into something more like our other neighbour, Venus, with temperatures way beyond boiling.
This is what we’re experiencing today: an atmosphere with a 50% increase in CO2 concentrations since pre-industrial levels, which is more than the increase that occurred naturally over the 20 000 years before the industrial revolution. This increase in the atmospheric CO2 concentration corresponds to global warming of about 1.1°C (2°F) since the 1850s.
And the natural carbon sinks, which remove CO2 from the atmosphere, can’t keep up with our increasing rate of emissions. And the more we emit, the less effective they’ll get.
The ocean is an important carbon sink that has absorbed over 30% of all anthropogenic (human-caused) CO2 emissions since the beginning of the industrial revolution.
Unfortunately, this has also made the ocean about 30% more acidic. Ocean acidification occurs as CO2 dissolves in the water, creating carbonic acid, forming bicarbonate by reacting with carbonate ions. Do you remember those ions?
Quick Recap of How This Cycle Affects Climate Change
Marine organisms consume carbonic ions in the slow carbon cycle, eventually bringing the carbon back down to the lithosphere. However, as the carbonic acid reacts with carbonic ions to form bicarbonate, the ions are lost to marine organisms, such as corals. But these organisms need the carbonate ions to create their shells, so with fewer ions to eat; the shell-building organisms are weakened as their shells grow thinner and more fragile. If we reach global warming of 2°C (3.6°F), this process means that all coral reefs could disappear.
Each year, forests absorb around 7.6 billion tonnes of CO2, about 1.5 times more than the U.S. emits yearly. On land, plants have absorbed about 25% of all anthropogenic CO2 emissions. However, as we know from the fast carbon cycle when plants decay or are consumed by fire, they emit the carbon they’ve stored. This means that forests can turn from carbon sink to carbon source through deforestation. And what are we doing all over the world?
We turn forests into agricultural and grazing land, turning carbon sinks into carbon sources. Looking at the three largest tropical rainforests in the Amazon, Congo River basin, and Southeast Asia, the Congo River Basin is the only one that remains a substantial carbon sink. In fact, the tropical rainforest of Southeast Asia has turned into a carbon source, emitting close to 500 million tonnes of CO2 each year.
As you’ve indeed gathered, the situation is dire. We’ve sped up the slow carbon cycle by removing carbon from the lithosphere (as fossil fuels), and the carbon sinks can’t keep up. If we have any chance of limiting further global warming, we need to decrease our emissions. Now. Care to help? Get started today with the Deedster app. Many small deeds make a… mighty deed?
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