Capturing carbon: why is it important?

And can we sequester carbon using nature-based solutions?
31 August 2021

Interview with 

Ruth Gregg, Natural England


photograph of a forest


Climate change has been top of the agenda recently, as the latest IPCC report came out earlier this month. The Intergovernmental Panel on Climate Change produces one of these reports every 6 to 7 years to summarise the 14,000 scientific papers that have been published on historic climate models, global warming and its implications on the planet. And the findings of this report are clear: humans are responsible for the planet warming at a rate that is unprecedented in at least the last 2000 years. This warming is driven by increased greenhouse gas emissions, of which CO2 and methane are the major contributors. This is already leading to hotter heatwaves, wetter monsoons, more frequent droughts, and the oceans warming at their fastest rate since the end of the last full Ice Age. Some of the impacts us humans have had on the planet are now irreversible. We are going to warm the planet by 1.5ºC more than pre-industrial levels. No matter what we do, sea levels are going to rise by several metres over the next 2000 years, the ice sheets will continue to melt and the oceans will become more and more acidic.

But, the science is also clear: there is hope. If we can reduce our global carbon emissions to net zero by 2050, the planet will quickly stop warming. And if we start absorbing more carbon than we produce it’ll even start cooling down again and those extreme weather events will become less extreme again. Sally Le Page spoke with Ruth Gregg from Natural England about the role carbon sequesteration could play...

Ruth - The absolute priority that we need to tackle is decarbonising the sectors that contribute to climate change, but also actively taking carbon dioxide out of the atmosphere.

Sally - That's Ruth Gregg, a climate change specialist who earlier this year produced a 240 page report for Natural England looking into climate change and carbon storage.

Ruth - What our report aims to do is that we look at all the habitats that you'll find in England, and we try and capture how important they are for carbon storage and sequestration. So what we cover is everything from peatlands that you find on our mountains and the hills, everything down to our coastal and marine sites and everything in between.

Sally - And this is what we hear referred to as carbon sequestration, right? To sequester carbon, to draw down carbon.

Ruth - It certainly is. So what carbon sequestration is; it's the process of capturing and storing atmospheric carbon dioxide. So habitats can do this as I've just described, but they can also do it in other ways as well, in that they can trap carbon. So when we're dealing with habitats such as reed beds or salt marshes or sea grass, they actually capture carbon that's been released from elsewhere and store it in their sediments.

Sally - And when we think about carbon capture, a lot of people will automatically think about carbon capture technologies and Elon Musk put forward a big prize to try and develop some tech that will draw down carbon from the atmosphere. Do you think that we can reach net zero using these technologies alone?

Ruth - So all the pathways that we have to get to net zero do take into account some of these technological developments that haven't actually happened yet. At the moment, the main carbon capture and storage that we have is our natural environment.

We'll be coming back to Ruth and nature-based solutions very soon. But first is it true that carbon capture technologies don't really exist yet? Naked Scientist, Harry Lewis, has been looking into how far we've come and how far we've yet to go with removing CO2 directly from the air.

Harry - I'm stood on the intersection of the South Circular that cuts across Putney High Street. Now, as you might be able to guess, this is one of the most polluted streets in London - the second, actually, according to a report released earlier this year. If our technology is responsible for pumping out pollution, then surely tech can be responsible for sucking it back up.

Harry - Carbon dioxide capture and storage, or CCS, is supposedly the answer. It's a label given to any technique with the potential to remove CO2 from the atmosphere and durably store in reservoirs. So CCS is often used to refer to the stripping of CO2 from waste streams, and it's already commonly used in the oil industry. Earlier in August, however, a research team pointed out that these techniques are less efficient than we previously thought. They require a lot of energy to make any tangible difference. Now, ironically, in this instance, the stored gas tends to be used for enhanced oil recovery, so it's injected into the ground in an attempt to force out any remaining oil deposits. Ultimately that then slowly leaks out of the wells and settles back in the atmosphere. Of the 21 large-scale plants across the globe, all but five sell their stores to facilities involved in this enhanced oil recovery.

Harry - So looking for alternatives, the other man-made carbon sequestration technique is direct carbon capture and storage - DCCS - technologies that suck the carbon straight from the air around us. There are currently three industrial-scale storage projects, and the biggest by far is the Canadian Weyburn carbon dioxide project in Canada. After starting back in 2000, the phase one trial found that the thick cap rock required for geological storage of the CO2 wasn't an impermeable barrier to the upward movement of the gas as is still commonly assumed. In order to capture the carbon dioxide in the first place, the Weyburn project filters air directly through a potassium hydroxide drenched filter. These plants are really energy hungry. A 2019 report from Imperial College London found that 30,000 large scale DCCS plants would be required to negate global emissions. Every year it would require the entire global supply of this chemical six times over. And even then it would still take up to a sixth of the world's energy expenditure to power them. The other issue is finding somewhere to store this gas. So as we've discussed, our understanding of geological foundations and their ability to hold onto carbon dioxide is fine in theory, but not so efficient in practice. Perhaps we could store the gas deep in the ocean as is done in Norway or by creating mineral carbonates. Maybe even utilise it in a different form of industry. That's like a company just outside Zurich who sell their CO2 to Coca-Cola.

Harry - Now, after walking around Putney, I stumbled across a sort of rudimentary direct carbon capture feature, a city tree, which might not be quite what you expect. It's an interesting little feature, really. It's roughly two metres high and around it is constructed this wooden lattice and trellis. And if you get really close, sprouting out the darkness between the shelves are dark and light shades of green. It's more like a small art installation, really. It's pretty out of place. It transpires that inside the cuboid are a large variety of different types of moss species, all of which are capable of drawing pollutants out of the air and supposedly making the air noticeably cleaner in a two to three metre radius.

It's obvious that direct carbon capture technologies are in desperate need of research and development. They're in need of incentivisation before they can make any real global difference. And stood here, I can't help but feel that in the next 20 years, it's preservation that's going to be essential. Something we still haven't entirely grasped. You know, the ecology and habitats that naturally suck up carbon. They're of paramount importance. Even if it is just to buy us some more time to learn from nature, like this little city tree, to help us further our technological efforts.

We don't have time to wait for carbon capture technologies to be developed if we want to reach net zero by 2050. So what's the alternative? Well Ruth Gregg reckons it's nature-based solutions.

Ruth - So what nature-based solutions are: they're about how protecting, restoring and managing natural systems can help societal problems. So it's looking at nature to provide us solutions and not just trying to use technology to help us out of these issues.

Sally - And what kind of problems can nature solve?

Ruth - We've already talked about mitigation and how habitats capture carbon in their vegetation, in their soils, but it can also help us with climate change adaptation, water regulation, water filtration. So we know that sensitive planting of woodlands on slopes, for example, can help us manage flood risk. Saltmarsh can help prevent or protect us from storm surges and sea level rise. So there's a whole host of benefits that they can give.

Sally - If we want to capture carbon with a nature-based solution, all of these buzz words, do we just plant trees? Is that it? Is the solution to climate change just trees?

Ruth - It's one of them. And it's a really important one. They offer us some of the most consistency sequestration rates and high sequestration rates. So they are a very vital piece of the puzzle, but you can only plant trees in so many places. We also need to consider what the marine and the coastal environments can offer us as well. So things like saltmarsh have been shown to store and sequester carbon at quite high rates. One of the things that we shouldn't be overlooking is protection of habitats, as habitats such as grasslands, our heathlands, have the potential to store huge amounts of carbon. And we want that carbon to stay where it is. We don't want that to be released. So no, not just trees, but trees are also very important.


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