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Can Carbon Capture Reverse Climate Change?

A new study shows why we should reduce emissions even faster.

Right now, there is a fevered buzz around carbon capture, which is only set to intensify over the coming years. Oil billionaires eye this technology as a route to greenwashing their way to vast mountains of future profits, while climate reports from the likes of the IPCC have found that this technology is crucial to meeting net-zero by 2050 and saving the planet from ourselves. This Jekyll and Hyde nature of carbon capture technology makes it one of the most controversial bits of climate tech out there. Despite this, there are cautious whispers and rumours that carbon capture has the potential to not only stop climate change but reverse the damage we have caused. As such, it can be used in the 2060s and 2070s to make up for us missing our 2050 net-zero goals (which we are on course to do) and, past that, even return the atmosphere and climate to a pre-industrial condition. But is carbon capture really such a get-out-of-jail-free card? A recent study set out to answer this question, and what they found was terrifying.

Before we look at this study, let’s first get a sense of scale here. According to the IPCC, CCS (Carbon Capture & Storage) needs to reach an annual capacity (i.e., the amount removed from the atmosphere each year) of 4.2 billion tonnes of carbon dioxide for us to reach net-zero. Now, to put this figure into perspective, the total amount of iron (one of the world’s most used materials) mined worldwide in 2022 was only 2.6 billion tonnes! To reach the IPCC’s CCS targets, the carbon capture industry has to scale up to become one of the world’s biggest industries.

Let’s say we do miss our climate targets, and after 2050, we are still emitting around 10 billion tonnes of carbon dioxide per year (nearly a quarter of our emissions today) until 2060 when we finally meet net-zero. If we wanted to use carbon capture in the 2060s and 2070s to repair this extra decade of atmospheric damage and take global carbon dioxide levels down to acceptable levels by the 2080s, we would need to more than double our CCS annual capacity to 9 billion tonnes of carbon dioxide.

Many serious scientists out there doubt that we can ever reach 4 billion tonnes of annual verifiable CCS, let alone 9 billion. Moreover, this is a very simplistic and optimistic way to model us overshooting our climate targets. In reality, we would likely need even more CCS capacity in the 2060s and 2070s to get us back on track if we carry on with our current level of progress.

So straight away, the premise of using CCS to make up for missing climate targets or using it to actively geoengineer the atmosphere to a pre-industrial condition is practically a far fetch. But, we are going to miss our climate targets, and it is crucial we understand how we can fight this and also what the consequences are for missing our targets.

As such, Korean researchers studied how removing large amounts of carbon dioxide from the atmosphere would affect the progress of local climate change. In effect, they wanted to see if lowering carbon concentrations in the atmosphere (rather than keeping it stable like the IPCC wants to do) really could reverse climate change and see if our get-out-of-jail-free card could actually work. In particular, they were interested in how vulnerable subtropical regions, such as Florida, Texas, India, and the Mediterranean, which suffer from more intense droughts and heatwaves as climate change progresses, would fare in this scenario.

How did they do this? Well, they used highly detailed computer climate models to examine a hypothetical future scenario in which carbon dioxide concentrations continued to rise from present-day levels for 140 years, then were gradually reduced back to the initial levels over another 140-year period. This might not sound like the scenario we have been discussing, as it happens over a far more extended period. In fact, this hypothetical scenario is impossible, as our fossil fuel reserves are set to run dry by 2060 anyway. But, it should give the researchers a highly exaggerated look into how CCS can affect climate change and if fixing the climate is as simple as reducing carbon concentrations.

Their model paid particular attention to a climate system known as the Hadley Cell. The Hadley Cell is a rotating wind which transports moisture from the equatorial regions to the tropics and subtropics. It is why the equator tends to have arid environments, while the tropics and subtropics tend to be more lush, with rainforests and alike. Scientists have known for decades that the Hadley Cell is highly influenced by climate change, and as the planet warms, it expands toward the poles. This means the humid air that rises from around the equator instead gets dumped at higher and higher latitudes, causing worsening droughts in subtropical regions.

The researchers wanted to see if the Hadley Cell would reduce back down to its original stomping ground in correlation with carbon removal and, in turn, if these subtropical climates can be saved using CCS.

Sadly, the results were not good. The researchers found that the subtropical climates would not return to normal for more than 200 years after reducing carbon dioxide concentrations. This means that in their hypothetical situations, areas like the Med and Texas were plagued with incredibly intense heatwaves, droughts, and wildfires.

But why?

Well, the researchers found that the Hadley Cell doesn’t return to its old shape and extent for more than 220 years after the carbon is removed. In the Northern Hemisphere, the Hadley Cell actually shrunk, meaning moisture from the equator fell in the tropics, making the subtropics (such as the Med and Texas) significantly drier and hotter. Whereas, in the Southern Hemisphere, the cell expanded towards the poles, pushing precipitation southwards, wreaking deadly havoc with the climate in South America and Australia.

This asymmetry was the smoking gun that led the researchers to their big insight. It’s all to do with ocean temperatures.

You see, the Hadley Cell is driven by the surface temperature difference between the scorching hot equator and cooler subtropics. The hot equator climate heats the air, causing it to rise, while the cooler subtropical climates cool the air, causing it to fall. This creates a circular conveyor belt of wind similar to a sea breeze but way larger and spanning across the globe.

However, there is far more ocean in the Southern Hemisphere, and the ocean has a far higher heat capacity than the land. This, in turn, causes this asymmetry in the Hadley Cell. You see, as the globe heats up, the vast majority of that heat energy is actually stored in the ocean, making the ocean a kind of giant thermal battery. It can hold so much heat, in fact, that it can take centuries for it to discharge its heat energy and cool down. So even once all the extra carbon has been removed from the atmosphere, the oceans will still be far hotter than they were before the carbon was added and will be for an awfully long time.

In the Southern Hemisphere, which is dominated by the ocean, this means the hot area where the air rises is larger, which in turn expands the Hadley Cell Southwards. In the Northern Hemisphere, which is mainly dominated by the land, this extra heat has the opposite effect, reducing the Hadley Cells’ extent.

Now, in the real world, we aren’t going to be emitting carbon dioxide at our current level for another 140 years, but we are on track to miss our climate targets and instead reach net-zero by the 2060s or 2070s. What’s more, CCS probably can’t get carbon dioxide levels back down to sensible levels until the end of the century. These extra few decades of emissions are enough to push climate change over the edge and become a worldwide catastrophe.

But, this study suggests that the damaging effects of climate change, such as droughts, heatwaves and wildfires, will stay with us well into the 2100s even if we use copious amounts of carbon capture to try and repair our damages, as the Hadley Cells likely won’t return to their original areas for decades after we return carbon levels to “normal”.

In fact, the study lead author, Seo-Yeon Kim, told space.com “I think that the main message of our study is that we should reduce carbon dioxide emissions now because afterwards, it gets really difficult,” and she went on to say, “We cannot control nature, we cannot reverse the consequences that easily; we cannot fix nature.”

So, no, carbon capture can’t reverse climate change. At least not in a way which can mitigate its deadly effects. Studies like this show that the Paris Agreement’s 2050 net-zero and 1.5 degrees Celsius of warming aren’t just arbitrary targets. They are a point of no return; once we go past these, there is no going back, and the damage will be locked in for decades and decades. In short, we must cut our emissions now and not rely on some future technological miracle to save us.

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(Originally published on PlanetEarthAndBeyond.co)