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Bankrupting the carbon budget Part I: Why are kids so angry?

We need carbon. We need water, too. But like all good things, there can be too much. Too little water and we die of thirst. Too much, we drown. The same with carbon. Too little in the atmosphere in the form of carbon dioxide (CO2), we go into an Ice Age. Too much, the planet broils. We know this because of the geological evidence and from fundamental laws of physics and chemistry.

How much carbon is there?

There is about 1.85 billion, billion tonnes of carbon on Earth. More than 99% is beneath our feet in soil and rocks including fossil fuels and permafrost. Just 0.2% or 43,500Gt is above the surface. Through natural processes, carbon is constantly in flux. That is, it’s moving between the land, the oceans, and living things (see ‘carbon cycle’ this website). When it’s burned, melted, or respired, it becomes a gas, combining with oxygen to make CO2. Some ends up in the atmosphere*. The rest is absorbed by terrestrial and oceanic ecosystems: forests, grasslands, wetlands, and marine animals and plants that make more than half the oxygen we breathe, and also as carbonic acid (H2CO3) dissolved in ocean and lake waters.

*Calculations at the bottom of this page.


A shift in time

It doesn’t take much CO2 in the atmosphere to warm the planet. Some 18,000 years ago, the concentration of CO2 was 189 ppm (parts per million). Global temperatures were 7-9°C cooler than today, and ice sheets several kilometres thick covered most of Europe and North America.

Over the next 10,000 years, the concentration increased 72ppm, to reach 261ppm. That was enough to warm the planet 6-8°C (Fig 2.).

Fig. 2: The blue line shows globally averaged surface air temperature from 24,000 years ago to the present day, compiled from paleoclimate records with a computer model of the climate system. The horizontal scale has been stretched for the past 1,000 years to show recent changes. Warming begins at the end of the last Glacial around 18,000 years ago, then temperatures stabilize around 9,000 years ago until the last 170 years, when excessive greenhouse gasses triggered rapid warming. (Image: Osman et al /Nature).
Fig. 2: The blue line shows globally averaged surface air temperature from 24,000 years ago to the present day, compiled from paleoclimate records with a computer model of the climate system. The horizontal scale has been stretched for the past 1,000 years to show recent changes. Warming begins at the end of the last Glacial around 18,000 years ago, then temperatures stabilize around 9,000 years ago until the last 170 years, when excessive greenhouse gasses triggered rapid warming. (Image: Osman et al /Nature).
 
By then, some 8,000 year ago, the warming had created a comfortable, and crucially a stable and predictable enough climate to enable humans to plant crops, domesticate livestock, and build civilizations. This land-use change added about 400Gt of CO2 to reach a concentration of 284ppm by the year 1850.
 
Courtesy of our planet’s eccentric orbit around the sun, the Earth was also entering a gradual cooling cycle that would ultimately lead to another Glacial epoch. This orbital obliquity largely compensated for the gradual warming effect of the extra carbon in the atmosphere. Aside from a few small climatic blips caused by volcanoes and the sun’s activity, the global climate remained stable enough for human civilization to reach a technological watershed moment: the Industrial Revolution.
 
To power this revolution, we dug carbon out of the ground and burned it to fuel ever-larger machines, fishing fleets, and massive land use changes to feed ever more people, destroying vast natural ecosystems that once locked away millions of tonnes of carbon. Their burned remains entered the atmosphere as CO2. (Slaughtering countless whales may have added quite a bit, too). In the 100 years from 1850 to 1950 we added, either directly or indirectly, another 450Gt of CO2 to the atmosphere, and so concentrations reached 310ppm.
 
It was about to get worse. Between 1950 and 2000—just 50 years—we added around 1050Gt; more than twice as much as we’d added the previous 7,950 years. Atmospheric CO2 passed 370ppm. Shoveling so much carbon into the atmosphere had postponed the inception of the next Glacial epoch by 100,000 years.
 
The terrestrial and ocean ecosystems that once supported us continued to being burned and bulldozed. And the pace of destruction kept increasing. The ocean, which had been absorbing more than 90% of the extra heat and as much as half the excess CO2, was becoming dangerously acidic. 
 
Twenty-one years later, on 21 April 2021, atmospheric CO2 passed 420ppm* for the first time in several million years. Our planet is now heating up faster than at any time since the comet wiped out the dinosaurs 65 million years ago. And the oceans are now absorbing only about 25% of it.
 

*The average for 2021 will be about 417ppm because atmospheric concentrations change between summer (lower) and winter (higher); see the graph below for an explanation.

The carbon budget

When governments signed the 2015 Paris Agreement they did so promising to keep global warming under 1.5°C by staying within a carbon budget. Each nation could choose how they would achieve this by reducing emissions—carbon ‘spending’—and increasing carbon ‘savings’ by planting carbon-absorbing trees. Obviously, to stay within the global budget, every nation had to play its part.

They didn’t. Emissions increased (Fig. 3)

Fig. 3: Emissions 2015-2021 * (projected (Image: co2.earth).
Fig. 3: Emissions 2015-2021 * (projected (Image: co2.earth).
In 2021, the IPCC presented a stark warning. Since the beginning of the Industrial Revolution, we’ve added about 2,400Gt of CO2 the atmosphere, around a third of which we added in just the past 20 years. To have a 66% of staying within 1.5°C, starting from January 2020, the world could emit no more than 400Gt of CO2. 
 
Emissions in 2020 were 38Gt. Emissions in 2021 are projected to be around 39Gt (Fig. 3). That leaves around 323Gt in the budget if we’re prepared to live with a 66% chance of keeping temperatures under 1.5°C. Or we can spend another 421Gt to have a 50% chance.
 

And only if one-way climate tipping points, don’t tip.

 

Tipping points are tipping

Scientists had been saying for decades that warming between 1 to 2°C would trigger catastrophic tipping points. At 1.2°C our climate is now already too hot to refreeze the 10,000 cubic metres of ice melting every second from Greenland’s ice sheet. So much freshwater entering the North Atlantic is already changing oceanic currents. This is triggering more tipping points in a cascade effect that will lead to irreversible chain reactions and rapid warming well beyond 3°C. Unless COP26 brings radical and immediate changes, the planet is destined to enter an entirely new ‘hothouse’ state, one we cannot control or reverse. And one hostile to our existence.
 

“The drama here is that one characteristic of tipping points is that once you press the ‘on’ button you cannot stop it; it takes over. It’s too late. It’s not like you could say, ‘Oops, now I realize I didn’t want to melt the Greenland ice cap. Let’s back off.’ Then it’s too late.” – Johan Rockström, Breaking Boundaries: The Science of Our Planet (Video 1)

Other tipping points are also pushing the carbon budget to the edge of a potential freefall. This includes vast areas of permafrost—frozen soil that contains an estimated 1,600Gt of carbon, almost twice the amount in the atmosphere today—is melting, disgorging CO2 and the far more potent greenhouse gas, methane into the atmosphere. And the Amazon rainforest, which could potentially releasing 200Gt of carbon into the atmosphere over the next 30 years. That is, by 2050. This process has already begun in south-east Amazonia (Video 2).
 
Earlier this year, the World Meteorological Organization stated that at least one of the next 5 years will be 1.5°C* warmer than pre-Industrial levels. And the chance of this happening is increasing with time.
 
Would you send your kids to school knowing they had just a 66% chance of coming home alive? Or 50% if we emit an extra 21Gt over the budget? And every day, the odds of their survival are getting increasingly worse because emissions are increasing. That’s what the carbon budget means for their futures.
 
Kids have done those simple calculations. And that’s why they’re so angry.
 
*The internal variability in any single year is estimated to be ± 0.25°C, so a single year at 1.5°C could be compensated if the following years are much cooler.
 
Video 1: in ‘Breaking Boundaries: The Science of Our Planet’, Sir David Attenborough succinctly explains tipping points. This is a short version of the full documentary of the same name, available on Netflix. 
Video 2: Amazon carbon tipping point

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  1. Bankrupting the carbon budget: Part II - COP26 - Climate Change & Nature: New Zealand
    22/11/2021 @ 3:13 pm

    […] Bankrupting the Carbon Budget: Part I, several tipping points were explained. Others are also tipping. For example, wildfires in the […]