The carbon cycle is key to understanding climate change | The Economist

published on July 2, 2020

The world has changed a lot in the past 1,000 years

But for most of that time one thing remained the same

the amount of carbon dioxide in the atmosphere

But in the late 18th century, this happened

and the levels began to climb

And then in the 20th century, it goes through the roof

It goes to levels that it’s not been seen at in nature for millions of years

The increase in atmospheric carbon

is the biggest contributor to climate change

The key to reversing the damage?

Restoring Earth’s delicately balanced carbon cycle

The way carbon moves around the Earth is known as the carbon cycle

It consists of sources which emit carbon into the atmosphere

and sinks, which take carbon out of it

The biological side of the carbon cycle is pretty near perfect

It works like this

respiration, for example, when animals breathe

emits carbon dioxide into the atmosphere

Then plants, bacteria and algae take CO2 out of the atmosphere

during photosynthesis, the process they use to generate chemical energy

Oceans are both sources and sinks

Carbon dioxide is endlessly being absorbed into the oceans

and released from the oceans at almost exactly the same rate

The system naturally balances itself out

If there’s more carbon dioxide being drawn down into the biosphere

then more carbon dioxide will be put back into the atmosphere

If the atmospheric level of carbon dioxide goes up

the levels by which it is absorbed by the oceans and the plants will go up too

It’s in what scientists call a dynamic equilibrium

But a few hundred years ago this dynamic equilibrium

was knocked out of kilter

When organisms die

some of the carbon stored inside them gets buried underground

stopping it from going back into the atmosphere

For hundreds of millions of years

this fossil carbon was left mostly undisturbed

until humans started to dig it up and burn it as fuel

The way humans have changed the carbon cycle

is one of the reasons some scientists say

the Earth has entered the Anthropocene

The geological age when human activity

is the dominant influence on the environment

Today, fossil fuels add an extra 95bn tonnes of carbon

into the atmosphere

Think about all the petrol that’s poured into all the cars

in all the cities in the world

Think about all the coal that’s going into all the power plants

in all the countries in the world

Think about all the gas that’s being burned

on all the burners of the stoves of the whole world

That’s what gives you 95bn tonnes

Roughly half of this extra carbon from fossil fuels

is absorbed by the Earth’s sinks

But the rest that makes it to the atmosphere, traps heat

warming the planet

This has had a devastating effect on the world’s climate

It also changes how well carbon sinks function

This is where things get complicated and scary

As temperature changes, the environment changes

and that may not be good for the sink

In the oceans, cooler water absorbs more carbon dioxide

So, as the oceans warm up, their ability to absorb carbon dioxide goes down

Plants photosynthesise more if there’s more carbon dioxide

which you would think is good

But plants synthesise less if they’re dead

And if the climate changes so that a large number of plants die

the photosynthesis of the planet will go down

Human action took a sledgehammer

to the Earth’s delicately balanced carbon cycle

The damage is not irrevocable—but only humans can fix it

The first thing to do if you want to

get the carbon cycle back into a stable balance is to stop pushing it

That means reducing human emissions from fossil fuels

as quickly as you can

Climate change has got to go

The growing green movement proves there is an appetite for that

But emissions aren’t being cut as severely as they need to be

At very best, you could say that

the rate at which carbon emissions from fossil fuels has grown

has maybe slowed a little bit

The international politics of climate change

makes cutting carbon emissions particularly difficult

You can find out why by clicking on the link above

But even if humans stopped using fossil fuels

and carbon emissions were zero

the amount of carbon in the atmosphere

would not return to pre-industrial levels

it would just stop growing

To bring atmospheric-carbon levels down

humans need to build systems that either create a new sink

or amplify the actions of an old sink

These are called negative-emission schemes

In terms of amplifying an old sink

you might restore a forest that has been degraded

You might change the way that you run pasture land

so that the soil stores more carbon

In terms of a new thing

you might actively suck carbon dioxide out of the atmosphere

and pump it back down into geology

This is known as direct air capture

Mechanical systems suck carbon dioxide out of the atmosphere

The carbon is then either stored underground or reused

for example, to make fuel

or to make new rock

Negative-emissions schemes work well

to offset some of the carbon humans emit

But when it comes to re-balancing the carbon cycle

they’re not a perfect solution

If you concentrate on negative emissions

then you’re kind of giving yourself licence to go on polluting

And that’s something that is a very dangerous trend

The second problem with negative emissions

they are relatively inefficient

Pulling tens, hundreds of billions of tonnes of carbon

out of the atmosphere through industrial means is a massive undertaking

The negative-emissions schemes that are being developed today

work on a very small scale

In order for them to actually have a positive, lasting impact

the world’s economic structure would need to change drastically

It’s like running the whole fossil-fuel industry in reverse and then some

That’s why relying on them

when we have nothing like the infrastructure or economic incentives

or history, to know that we’re going to do them is such a dangerous idea

At some point humans will stop burning fossil fuels

either by choice or by force

By the time that happens the world will look very different

to what it does now

It took just a few hundred years to destroy the

dynamic equilibrium of the carbon cycle

But it’ll take many hundreds more to restore it

I’m Oliver Morton I’m the briefings editor at The Economist

We’ve written a series of climate briefs to cover the basics

and a bit more than the basics on all sorts of aspects

of the climate crisis that is facing the Earth

You can read them all at the link opposite

Thank you for watching

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