Carbon dioxide removal won’t reverse climate change

Taking carbon dioxide out of the air won’t be enough to stop the harm caused by rising temperatures.

Carbon dioxide can be removed from the atmosphere in a variety of different ways, from planting trees to burying it deep underground.

These approaches, collectively known as carbon dioxide removal, have often been touted as a silver bullet in the fight against climate change. It’s been suggested that if global temperatures surge above 1.5⁰C of warming, then this approach could bring the temperature back down again and stabilise the climate.

While this might seem to be a viable alternative to cutting emissions to some, new research shows that’s not the case. Overshooting 1.5⁰C will lead to changes in ecosystems, weather patterns and sea level that can’t easily be undone even if temperatures are eventually brought back in line.

Instead, the study shows that rapid and deep cuts to greenhouse gas emissions are the best way to avoid the most devastating impacts of climate change. Dr Carl-Friedrich Schleussner was its lead author.

“Our work reinforces the urgency of governments acting to reduce our emissions now, and not later down the line,” Carl-Friedrich says. “The race to net zero needs to be seen for what it is – a sprint.”

“Only by doing much more in this critical decade to bring emissions down and peak temperatures as low as possible, can we effectively limit damages.”

The findings of the study were published in Nature.

What is carbon dioxide removal?

It’s now considered increasingly likely that the world will pass 1.5°C of warming. Greenhouse gas emissions need to fall by almost half by 2030 to keep the planet on track to meet this target but are currently still rising.

The Climate Action Tracker, produced by a team of independent researchers who monitor progress on climate change, now believe the world will be 2.7°C hotter in 2100 than it was 200 years earlier. Humans have never experienced an Earth this warm, which will change the climate, ecosystems and our lives beyond recognition.

It is argued that one necessary part of limiting such extreme global warming is through carbon dioxide removal, or CDR. This covers a wide variety of techniques that remove carbon from the atmosphere, from natural processes like restoring wetlands to technical solutions such as carbon capture.

Reports from leading climate bodies like the Intergovernmental Panel on Climate Change currently see CDR being used as a way of mitigating the emissions of industries where it can be difficult to cut greenhouse gas emissions, like construction or agriculture.

The use of CDR could theoretically also go further and be used to not just reach net zero emissions, but to reach net negative. This would see Earth absorbing more carbon dioxide than it emits for the first time in centuries, and would gradually cool the planet over many years.

This approach is controversial, however. Some see CDR as a justification to continue using fossil fuels, a smoke screen for oil companies to continue extraction, or a technology that will never deliver on its promises.

What impact would a climate overshoot have?

To assess what impacts a overshooting 1.5⁰C of warming might have on Earth, the researchers simulated a variety of different future scenarios. They focused on futures that would achieve net zero by around 2050 and limit warming close enough to 1.5⁰C that CDR could feasibly bring temperatures back to that level by the end of the century.

Two types of possible futures stood out. In the first, temperatures peaked above 1.5⁰C but were brought down over time by CDR. This requires a drastic increase in our ability to take carbon dioxide out of the atmosphere, with our current capacity needing to increase by 1,000 times by 2050 to keep the 1.5⁰C target in sight.

As our current climate models are based on averages, even more CDR may be needed if reality is more extreme than the predictions.

Going over 1.5⁰C also brings the risk of passing climate tipping points. The researchers found that for every century of overshoot above this limit, sea levels in 2300 will be 40 centimetres higher than they would otherwise have been. The thawing of permafrost will also add another 0.02⁰C for each 100 years, making the task of bringing temperatures down even more difficult.

In the other set of scenarios, temperatures peaked at or near 1.5⁰C so that CDR isn’t initially needed. This means it can instead be used to buffer global warming if temperatures rise more than expected, offering room for manoeuvre that the other climate scenario just can’t accommodate.

In any event, the paper says that we must urgently begin ramping up our ability to limit climate change in the coming decades. Gaurav Ganti, a co-author from Climate Analytics, says that increases in CDR must go hand in hand with ambitious emissions cuts.

“There’s no way to rule out the need for large amounts of net negative emissions capabilities, so we really need to minimise our residual emissions,” he explains. “We cannot squander carbon dioxide removal on offsetting emissions we have the ability to avoid.”

The researchers hope that, when the nations of the world meet for the COP29 climate conference in November, they will begin to deliver on this ideal.