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This week's long read (3 of them as they are not that long, and the last one is a silly)

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Will sucking carbon from air ever really help tackle climate change?

The direct air capture industry got a boost last week with the opening of Mammoth, the largest plant yet for sucking carbon dioxide out of the atmosphere, but questions remain about whether the technology can scale up

By Madeleine Cuff

15 May 2024




The Mammoth direct air capture plant in Iceland is the largest in the world



Humanity has spent the past few centuries releasing ever greater amounts of carbon dioxide into the atmosphere – a state of affairs that must be reversed if we are to get to grips with climate change. Removing such CO2 in a process called direct air capture (DAC) has been on the cards for some time, but finally, after years of research and small-scale pilot projects, giant carbon-sucking facilities are becoming a reality. The question is, will the industry grow large enough, fast enough?

DAC got a big boost last week when Swiss company Climeworks switched on a new plant called Mammoth. This can extract up to 36,000 tonnes of CO2 a year from the atmosphere – living up to its name, at least when compared with its predecessor Orca, which boasted a maximum capture capacity of just 4000 tonnes per year.


The new plant instantly quadrupled global capacity for DAC and is a sign of a step change under way in the industry. Mammoth will only hold the title of world’s largest DAC plant until next year, when the Stratos plant, built by a subsidiary of energy firm Occidental Petroleum using technology from Canadian DAC company Carbon Engineering, comes online. It will be able to extract half a million tonnes of CO2 a year.

Steve Smith at the University of Oxford says Mammoth and Stratos are the start of a rapid expansion in global direct air carbon capture and storage (DACCS) capacity. “A dozen or so more DACCS projects are planned to go live in the next couple of years, by various companies,” he says. “If these all materialise, DACCS capacity could be nudging 800,000 tonnes per year.”

Overall, ambitions are high – both Occidental and Climeworks plan to be operating multiple plants with capture capacities of 1 million tonnes apiece by 2035.


This rapid expansion is being driven by two factors. The first is corporate interest in carbon removals, with the likes of Microsoft, Stripe and Coca-Cola buying DAC credits to help offset their own emissions. With the reputation of many traditional carbon offset schemes in tatters, DAC is seen by some large firms as one of the last respectable removal options.

Government policy has also been instrumental, particularly in the US. President Joe Biden’s administration is spending $3.5 billion to support four DAC “hubs” in the US, including Stratos, as part of measures passed in the Inflation Reduction Act to drive carbon removal efforts across the country. US federal tax credits also provide support of up to $180 per tonne of CO2 trapped and permanently stored via DAC, the first major policy of its kind anywhere in the world.

But voluntary carbon credits and generous government subsidies will only take the industry so far. Pathways to limit warming to 2°C will require billions of tonnes of carbon to be removed from the atmosphere by mid-century. For DAC to make a meaningful contribution to that, “some form of regulation by governments” will be necessary to drive the growth of this sector, says Smith.

For example, in February European Union officials outlined plans to create “a European single market for industrial carbon management” by 2050, to ensure all residual emissions from sectors such as livestock farming are balanced with equivalent removals. But the plans are still in their infancy and are yet to be approved by member states.


Another major hurdle is cost. For the DAC industry, the race is on to cut removal costs before government subsidies and corporate budgets run dry. Operators are hoping that by scaling up the size of facilities, the sky-high price of sucking carbon out of the air will come down rapidly, from around $600-$1000 per tonne today to $100-$200 per tonne within the next few decades. That price point would make DAC capable of delivering globally significant levels of carbon removal, most experts agree, but few are sure such a dramatic price drop is possible.

“The science was done 50 years ago. This has always been about the ability to do things at industrial scale, cheaply,” says David Keith at the University of Chicago. “The challenge is whether you can do it at an interesting cost, and I don’t think we know the answer to that yet.”

There are also reputational challenges to consider. Big oil companies including Occidental, ExxonMobil and Shell are all eyeing DAC as a way to justify squeezing more oil from reservoirs, reducing the net carbon footprint of their fossil fuels business on an ongoing basis. Rather than extending the lifespan of the fossil fuel industry, Smith stresses the focus should be on cutting global emissions and developing DAC as a way of tackling any residual, hard-to-abate emissions. He describes DAC as the “carbon equivalent of litter-picking: hard work, expensive, not the first-best way to deal with the problem, but necessary in our imperfect world”.

Some people doubt DAC will ever make a meaningful contribution to global pollution drawdown. Howard Herzog at the Massachusetts Institute of Technology Energy Initiative believes the technology is “overhyped”, citing uncertainty over its future costs and high energy demand.

Even Keith, who founded the DAC business Carbon Engineering, says that other methods of carbon removal, such as boosting the carbon storage capacity of soils or ocean waters, hold at least as much promise. “Direct air capture is one of many different carbon removal pathways,” he says. “I don’t see it as being unique.”


To rescue biodiversity, we need a better way to measure it

There are all kinds of different ways to measure biodiversity. But if we are to arrest its alarming decline, biologists must agree on a method that best captures how it changes over time

By Graham Lawton

20 May 2024



2CA2RF4 meadow with a lot of colorful flowers

Biodiversity contains several dimensions

Hans-Joachim Schneider/Alamy


At first blush, the idea of biodiversity seems simple enough. It is essentially the variety of all life on Earth. But making sense of biodiversity in a way that can help us halt or even reverse its decline is anything but straightforward.

“People often use the word biodiversity just to mean any characteristic of life out there that we might care to protect,” says Mark Vellend, a biologist at the University of Sherbrooke in Quebec, Canada. “That’s not a definition I find useful in science because if it’s everything, it’s nothing.”


For biodiversity to be a valuable concept, he says, it needs to be a measure of biological variety. That way, we can not only assess where we are and where we are headed, but also how best to conserve the biodiversity we have left.

The problem is that variety itself comes in many forms, especially in biology. “You can’t just come up with a single number for biodiversity in the same way as you can for carbon,” says Andy Hector at the University of Oxford. “It’s way, way more complicated.”

We already have ways to measure biodiversity. That’s how we know it is in steep decline. They boil down to what biologists think of as dimensions of biodiversity. One of the most basic is species richness, which is simply the number of species in a given place at a given time. This has been used extensively and can sometimes be a useful proxy for other dimensions of biodiversity, says Hector.

Measuring biodiversity

One of those is the relative abundance of the different species. Two ecosystems can be equally rich in species, but not in diversity. “The way I like to explain it is if you walk through a forest or swim through a coral reef and you see two organisms in sequence, what are the odds that they’re going to be different things?” says Vellend. “You could have a thousand types of things in there, but if 99 per cent of them are of one type, then the odds are, when you see two in a row, it’s going to be the same thing.”

A third dimension is how different the species are from one another in some important aspect. “Functional diversity”, for example, looks at the range of different roles that species play in an ecosystem, such as in photosynthesis, nutrient recycling, predation or pollination.

But there is also a fourth dimension, which tracks how the other three change over time. Every measure of biodiversity worth its salt captures one or more of these aspects, weighted according to what data is available and the project’s goals. “It all depends what you want,” says Hector. “Are you trying to conserve biodiversity for biodiversity’s sake or is it more human-centric?”



And here’s where things get knotty, because there are myriad ways of measuring each dimension. That means the whole thing risks becoming frighteningly fractal and indeed fractious. When discussions started on how to define the 2020 global biodiversity targets, there were nearly 100 suggestions on the table, according to Henrique Pereira at the University of Halle-Wittenberg in Germany.

In 2013, researchers led by Pereira began trying to standardise the way biodiversity is measured. They distilled biodiversity to six key dimensions: genetic composition, species distribution and abundance, species traits, community composition, ecosystem functioning and ecosystem structure. These capture the essence of biodiversity and how it is changing in a format that biologists can measure and share, says Pereira.

Not everyone is on board. But there is at least a growing realisation that the time for such quibbling has long passed. There isn’t, and probably never will be, a comprehensive measure of biodiversity, says Hector. And ultimately, “we don’t have the luxury of waiting until all life is documented”, he says.


Could we live in tree cities grown from giant sequoia in the future?

This week our new Future Chronicles column, which explores an imagined history of inventions of the future, visits carbon negative cities: forest homes grown from giant sequoia, genetically engineered for rapid growth. Rowan Hooper is our guide

By Rowan Hooper

22 May 2024



Sunny road in Oregon sequoia forest, USA; Shutterstock ID 2279027835; purchase_order: -; job: -; client: -; other: -

Oregon sequoia forest, USA



In the second half of the 21st century, the first living city was established in urban forest around Portland, Oregon. Sequoia City comprised a grove of 40 trees, including a hospital tree, schools, farms and recreation facilities (zip lines, slides and altitude swings). As they grew, residential trees eventually each housed dozens of families, living in custom-grown rooms made of living plant tissue. Children raised in Sequoia City saw no distinction between humans and other lifeforms. To them, ecology – the study of life in relation to its environment – was something they understood in their bones. That they were connected to nature went without saying; their intimacy was innate.

Sequoia City was a demonstration settlement, established to provide the proven mental health benefits of living in nature, to support the storage of carbon in living trees and soils and to tackle the extinction crisis.

It was inspired by ecologists who had discovered other species that had domesticated plants to live in. Philidris ants in Fiji sow seeds of Squamellaria on the branches of large trees. The ants tend the seedlings, which, as they grow, form large, hollow structures called domatia. The ants are saved the effort of building a nest and move into the domatia. The Squamellaria produce fruit too, which the ants eat. Descendant ants plant more seeds taken from their crop and the symbiotic cycle carries on.

The planners behind Sequoia City saw what the ants were doing and thought it looked like a good idea. Inspiration also came from living tree cities in science fiction, such as Cixin Liu’s Remembrance of Earth’s Past trilogy.

Giant sequoia are some of the largest organisms to have existed on our planet. They can live for up to 3000 years and grow up to 90 metres tall. In the early 21st century, their numbers fell in their native range in the Sierra Nevada mountains of California due to the climate crisis, but they continued to grow well in wetter, more northerly regions such as northern Europe and the Pacific Northwest. Oregon was chosen as the first location for a living city.

There were a few problems to overcome in developing the residential trees. The biggest was the slow growth of sequoias. Although faster-growing than the likes of oak, sequoia still take at least 100 years before they are big enough to live in.

However, the genome sequence of giant sequoia was well known, and our understanding of the genetics of plant growth was sophisticated enough even back in the 2020s to locate genes related to fast growth. With careful gene editing, it was possible to create sequoia that develop ultra rapidly. The key DNA sequences came from eucalyptus, one of the fastest growing trees, and bamboo, which, despite being a grass not a tree, supplied some important traits that enabled the development of a suitable species of sequoia.

The resulting trees formed their own version of domatia, encouraged by inserting guiding bars into the plant tissue. Different sized rooms could easily be grown, and windows installed. Bathrooms and toilet facilities were fully plumbed. Sewage was processed by specialised microbes and recycled into soil at the base of the tree and in the numerous gardens high in the tree itself.

Epiphytes – plants growing on other plants – are diverse and important parts of the forest ecosystem. In Sequoia City, garden zones and farm zones grew a range of squashes, cereals and beans, which the residents both consume and trade. Small cherry and apple trees themselves grew in orchard zones supported by the giant sequoia. Water farms on the trees deployed bromeliads, ferns and mosses to trap moisture from the air and send it down pipes to storage domatia. Electricity was supplied by wind and solar installations on individual domatia and on specialised power trees.

The success of Sequoia City spawned a series of copies around the world that used gene-edited species native to their region: Oak City and BeechTown in the UK, Bamboo MegaCity in southern China and Gum Towns, made of eucalyptus, in Tasmania and New South Wales in Australia. The domestication of the baobab and its subsequent gene-editing for accommodation led to spectacular Baobab towns in Ghana, Kenya and Sudan. By the end of the 21st century, satellite surveys of tree cover confirmed a significant fraction of previously deforested land had been regreened, and estimates suggested that the tree cities had contributed to a large reduction in atmospheric carbon dioxide. Studies reported that species diversity and population sizes had returned to levels not seen since the 19th century.

Tree children, immersed in the arboreal high life, traditionally got their first pair of wings – modified hang gliders – at age 10.


Living-tree homes

Time stamp



The ultimate in eco-living

Future Chronicles explores an imagined history of inventions and developments yet to come. Rowan Hooper is the podcast editor at New Scientist and author of How to Spend a Trillion Dollars: The 10 global problems we can actually fix.


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Re the carbon capture.  What form does the 36,000 tons of removed carbon take?  Solid blocks of graphite?  Or a CO2 gas that has to be pumped somewhere like a disused gas well to store it?


How much energy does such a capture system use and how much new CO2 is released in providing that energy?

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1 minute ago, ProDave said:

Re the carbon capture.  What form does the 36,000 tons of removed carbon take?  Solid blocks of graphite?  Or a CO2 gas that has to be pumped somewhere like a disused gas well to store it?


How much energy does such a capture system use and how much new CO2 is released in providing that energy?

A fluid that has to be pumped and stored usually.


Have read that to capture CO2 from a coal plant takes 30% more energy, natural gas 25%.  Not sure how accurate those numbers are and it was a decade or more ago I saw it.

There is this article that claims that it is at parity.


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The article on biodiversity is interesting, especially considering the April requirement for ‘Net Gain’. Exactly how LPAs are going to measure that is the question. A whole new set of buzzwords coming up…

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I feel that there is a risk that the 'big boys' will just put money into DAC and then not do anything about what they / we are creating in the first place


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