What You’ll Learn In This Module

• Is too much carbon a problem?
• What is the carbon cycle?
• What is a carbon sink?
• What is carbon sequestration?
• What is a carbon footprint?
• What is a carbon budget?

Is too much carbon a problem?

Carbon is essential to our lives, and it makes up the food we eat and the air we breathe.

The amount of carbon on Earth hasn’t changed. But what has changed is the location of the carbon.

There is now much more carbon in the atmosphere as carbon dioxide than there was before.

This is because the carbon stored under the Earth’s surface for millions of years, as coal, oil, gas and peat, has been removed by man.

These fossil fuels have been burned, releasing carbon into the atmosphere.

The last time that carbon levels in the atmosphere were this high was probably about 2-3 million years ago.

It happened when the Earth was a lot warmer and the oceans were around 20 meters higher.

Humans did not have to worry about living in such an environment, since they were not yet in existence.

What is the carbon cycle?

To understand better what is happening here, it’s helpful to know about the carbon cycle.

Carbon Dioxide in the air is turned into oxygen by plants, which store the carbon and release the oxygen through a process known as photosynthesis.

When plants die, they usually either decompose or burn and release the carbon back into the air.

We know this process as the carbon cycle.

But if these trees and plants live in a swamp or bog or the Ocean, this might not happen.

Instead, they may be fossilized, trapping the carbon.

This effect is small on a year-by-year basis. But over millions of years, a mass of carbon has been stored under the surface of the Earth as, e.g. peat, oil, natural gas and coal.

The amount of this stored carbon is much larger than the amount of carbon usually found in the atmosphere.

Humans discovered these stores and started to remove the peat, oil, gas and coal as energy, e.g. for heat.

Since the industrial revolution (1760–1840) however, carbon in the Earth has suddenly been released in torrents.

So much CO₂ has been released that the Earth’s temperature is rising quickly, changing its climate.

It has increased by around 1.2°C over the last century.

This is faster than the rate of change between the last ice age and the current warm period.

What is a carbon sink?

A carbon sink is something that absorbs more carbon than it releases into the atmosphere.

The three most important carbon sinks on Earth are (i) the Ocean, (ii) Soil and (iii) Forests.

A carbon source is the opposite – it’s something that releases more carbon into the atmosphere than it stores.

While the amount of carbon in our world does not change, its location is continuously evolving. It flows between our atmosphere and organisms on Earth through the process known as the carbon cycle.

It’s a process that has been perfectly balanced for thousands of years.

But now, human activity is releasing more carbon into the atmosphere than the Earth’s natural carbon sinks can absorb.

Re-building, expanding and strengthening Earth’s natural carbon sinks are part of the necessary actions to tackle climate change – to draw down the carbon from the atmosphere.

So far, we do not have modern technology that can do this for large amounts of CO₂.

We will need to learn how to support and strengthen nature in this task.

Take a look at each of the major carbon sinks:

1. The Ocean

The Earth’s oceans are the world’s largest carbon store, with an estimated 90% of the carbon cycle being circulated through marine waters.

Since the industrial revolution, the Earth’s oceans have absorbed about a third of the CO₂ produced by human activity and around 90% of the heat generated by global warming.

Phytoplankton is one of the organisms supporting the Ocean as the largest carbon sink.

These tiny algae and bacteria absorb as much carbon as all the plants and trees on the land combined.

When they die, they sink to the deep ocean, and the carbon they store forms an enormous carbon reservoir.

But the increased heat from global warming is changing the ocean currents, affecting the movement of Phytoplankton, an important food source for many marine animals.

The increased concentration of CO₂ is also making the water more acidic, especially deadly to shellfish and corals.

While most countries discuss targets to reduce land-based emissions, the world’s oceans have been largely ignored.

Restoring and conserving marine ecosystems such as mangroves, seagrasses, and salt marshes would help the oceans process the increased carbon dioxide levels.

The support and strengthening of a healthy ocean are also key.

• The shipping industry is currently producing around 3% of global greenhouse gas emissions and this is expected to increase strongly over the next 25 years.
• A shift towards sustainable fisheries would ovoid overfishing and also reduce carbon emissions associated with the industry.
• Plastic pollution has been reducing plankton’s ability to absorb CO₂.

For more on the role of the oceans in regulating climate change and storing carbon, read here.

2. Soil

The Food and Agriculture Organization of the United Nations estimates that the top 30cm of the world’s soil contains around 680 billion tons of carbon – about double the amount in the atmosphere.

Particularly wet organic soils, such as peatlands, forest soils and permanently frozen ground (permafrost) store a lot of carbon.

Yet practices such as draining peatlands, burning the peat for heat, drying the peat for use in garden composts, and ploughing up pastures and croplands are degrading the soil and releasing previously-stored carbon into the atmosphere.

Healthy soils are essential not just for food production but also for tackling climate change.

Healthy soils and land ecosystems can capture carbon dioxide from the air and store it.

Improving the health of soils through, e.g. restoring degraded soils, allows them to draw down and store more carbon dioxide from the atmosphere.

Restoring critical ecosystems on land, and ensuring the sustainable use of land in urban and rural areas, can help us mitigate and adapt to climate change.

For more on the role of soil in regulating climate change and storing carbon, read here.

3. Forests

It’s estimated that trees worldwide absorb about 2.6 billion tons of carbon dioxide every year, and they have absorbed an estimated third of our emissions since the industrial revolution.

Trees and plants absorb CO₂ from the air and use it to build their leaves, stems and roots, storing the carbon.

They are an essential carbon sink playing a vital role in helping to counterbalance the damage done by humans through burning fossil fuels.

Yet, forests are rapidly disappearing around the world. In the last 60 years, it’s estimated that more than half of the tropical forests worldwide have been destroyed.

And forests are being degraded. This is when they are damaged or weakened, reducing their ability to draw down and store carbon from the atmosphere.

In addition to carbon dioxide absorption, forests:

• house wildlife, 
• provide natural beauty, 
• reduce the risk of floods, 
• purify rivers, 
• reduce urban air pollution, 
• benefit human wellbeing and recreation, 
• and provide timber for wooden buildings which can hold carbon captured for centuries.

Forests need to be re-planted, used sustainably and protected.

For more on the role of forests in regulating climate change and storing carbon, read here.

What is carbon sequestration? 

Carbon sequestration is the process of capturing carbon dioxide from the atmosphere and storing it in the Earth.

It’s one of the methods to reduce the amount of CO₂ in the atmosphere and therefore to reduce global climate change.

Biologic carbon sequestration is the natural absorption and storage of CO₂ by e.g. forests, plants, soils and the oceans.

There are also ongoing attempts to find technological solutions to draw down and store carbon.

For example, geologic carbon sequestration is a process of storing CO₂ in underground geologic formations. The CO₂ is pressurized until it becomes a liquid which can be injected into an underground store.

What is a carbon footprint?

A carbon footprint is the amount of greenhouse gases that are produced by a particular activity.

For example all of your daily activities over the period of a year; the activities of a company, organization or country over a specified period of time; or even by an event, a place or a product.

In 2017, the global average annual carbon footprint per person was about 5 tons of CO₂. 

A country’s overall carbon footprint is usually larger than just the emissions it produces within its territorial boundaries. This is because of the goods and services it imports.

These emissions are also sometimes called consumption emissions because we’re consuming a product that is producing emissions.

Territorial emissions are emissions that are actually produced within the territorial boundaries of a country.

Take the example of a country that imports steel. Steel is produced through an industrial process that produces greenhouse gas emissions. A country importing steel is therefore also responsible for emissions being produced in another country, where the steel is actually produced.

What is a carbon budget?

A carbon budget is the amount of carbon dioxide emissions that are permitted over a specified period in order to keep within a certain warming-related target or threshold.

We know that the world’s temperature level responds to the amount of accumulated carbon dioxide in the atmosphere.

If we want to keep the average global temperature to e.g. within 1.5 degrees of its preindustrial level, we have to stop the accumulated amount of carbon dioxide in the atmosphere from rising above a certain level.

We can calculate the total amount of CO₂ that can be released into the atmosphere before the temperature would increase above our temperature target.

This amount of CO₂ is called the carbon budget.

How can we reduce our carbon footprint? By moving away from fossil fuels and towards green energy from renewable sources.