Direct carbon capture from water, not air

From New Atlas

The oceans soak up enormous quantities of carbon dioxide, and MIT researchers say they've developed a way of releasing and capturing it that uses far less energy than direct air capture – with some other environmental benefits to boot.

Pulling greenhouse gases out of water is an odd-sounding idea, but the oceans are the planet's number one carbon sink, and direct air carbon capture has pretty serious problems: it costs a lot, and uses a lot of energy. According to IEA figures from 2022, even the more efficient air capture technologies require about 6.6 gigajoules of energy, or 1.83 megawatt-hours per ton of carbon dioxide captured.

Most of that energy isn't used to directly separate the CO2 from the air, it's in heat energy to keep the absorbers at operating temperatures, or electrical energy used to compress large amounts of air to the point where the capture operation can be done efficiently. But either way, the costs are out of control, with 2030 price estimates per ton ranging between US$300-$1,000. According to Statista, there's not a nation on Earth currently willing to tax carbon emitters even half of the lower estimate; first-placed Uruguay taxes it at US$137/ton. Direct air capture is not going to work as a business unless its costs come way down.

It turns out there's another option: seawater. As atmospheric carbon concentrations rise, carbon dioxide begins to dissolve into seawater. The ocean currently soaks up some 30-40% of all humanity's annual carbon emissions, and maintains a constant free exchange with the air. Suck the carbon out of the seawater, and it'll suck more out of the air to re-balance the concentrations. Best of all, the concentration of carbon dioxide in seawater is more than 100 times greater than in air.

Previous research teams have managed to release CO2 from seawater and capture it, but their methods have required expensive membranes and a constant supply of chemicals to keep the reactions going. MIT's team, on the other hand, has announced the successful testing of a system that uses neither, and requires vastly less energy than air capture methods.

In the new system, seawater is passed through two chambers. The first uses reactive electrodes to release protons into the seawater, which acidifies the water, turning dissolved inorganic bicarbonates into carbon dioxide gas, which bubbles out and is collected using a vacuum. Then the water's pushed through to a second set of cells with a reversed voltage, calling those protons back in and turning the acidic water back to alkaline before releasing it back into the sea. Periodically, when the active electrode is depleted of protons, the polarity of the voltage is reversed, and the same reaction continues with water flowing in the opposite direction.

In a new study published in the peer-reviewed journal Energy & Environmental Science, the team says its technique requires an energy input of 122 kJ/mol, equating by our math to 0.77 mWh per ton. And the team is confident it can do even better: "Though our base energy consumption of 122 kJ/mol-CO2 is a record-low," reads the study, "it may still be substantially decreased towards the thermodynamic limit of 32 kJ/mol-CO2."

The team projects an optimized cost around US$56 per ton of CO2 captured – although it's not fair to compare that directly against full-system direct air capture costs. The study cautions that this does not include vacuum degassing, filtration and "auxiliary costs outside of the electrochemical system" – analyses of which will have to be done separately. Some of these, however, could potentially be mitigated by integrating the carbon capture units in with other facilities, for example desalination plants, which are already processing large volumes of seawater.

There are some other benefits too; increased carbon buildup in the ocean over recent years has already caused problems with acidification, threatening coral reefs and shellfish. The alkaline output of this process, if directed where it's needed, could help redress the balance.

The team has a practical demonstration project planned for sometime in the next two years, and says there are plenty of things that still need work. For one, the researchers would love to be able to separate the gas out without a vacuum system. And mineral precipitates are fouling the electrodes on the alkalinization side, so there's plenty of progress yet to be made.

The study is open access in the journal Energy & Environmental Science.

A new powder which captures CO2

The carbon-capturing powder, pictured on Berkeley's campus. Photograph: Zihui Zhou/University of California, Berkeley

From The Guardian

An innocuous yellow powder, created in a lab, could be a new way to combat the climate crisis by absorbing carbon from the air.

Just half a pound of the stuff may remove as much carbon dioxide as a tree can, according to early tests. [Over the tree's life? Over a week?]Once the carbon is absorbed by the powder, it can be released into safe storage or be used in industrial processes, like carbonizing drinks. [Aerating drinks doesn't permanently remove CO2 from the atmosphere, since the gas is released when the bottle or can is opened.]

“This really addresses a major problem in the tech field, and it gives an opportunity now for us to scale it up and start using it,” says Omar Yaghi, a chemist at the University of California, Berkeley. It’s not the first material to absorb carbon, but “it’s a quantum leap ahead [of other compounds] in terms of the durability of the material”.

The powder is known as a covalent organic framework, with strong chemical bonds that pull gases out of the air. The material is both durable and porous, and can be used hundreds of times, making it superior to other materials used for carbon capture.

Yaghi has been working on similar materials for decades. It’s part of a broader push to collect tiny amounts of carbon from the air – either from power plants or from air around cities. Yaghi’s research with Zihui Zhou, a graduate student in his lab, and others was published in the journal Nature last month.

In the lab, Yaghi’s team tested the new powder and found that it could successfully absorb and release carbon more than 100 times. It fills up with carbon in about two hours, and then must be heated to release the gas before starting the process over again. It only requires a temperature of about 120F to release the carbon; that makes it an improvement over other methods, which require a much higher temperature.

That feature means places that already produce extra heat – such as factories or power plants – could use it to release the gas and start the cycle again. The material could be incorporated into existing carbon capture systems or future technology.

Yaghi says he could imagine a future in which people build large plants using the material in every city of 1 million people or more around the world. He has plans to scale the use of this type of carbon capture with his Irvine, California-based company, Atoco, and believes the powder can be manufactured in multi-ton quantities in less than a year.

Shengqian Ma, a chemist at the University of North Texas who was not involved in the new work, says this technology could be gamechanging. “One longstanding challenge for direct air capture lies in the high regeneration temperatures,” he says, adding that the new material can substantially reduce the energy needed to use direct air capture, making it “very novel” and “very promising”.

“We need to reduce our greenhouse emissions, and we need to do it fast,” says Farzan Kazemifar, an associate professor in the department of mechanical engineering at San Jose State University who was not involved in the new study. “In the short term, replacing large emitters of carbon dioxide – like coal power plants – with renewable electricity offers the fastest reduction in emissions. However, in the long term, in case the emissions don’t go down at the desired pace, or if global warming effects intensify, we may need to rely on technologies that can remove carbon dioxide from the atmosphere, and direct air capture is one of those technologies.”

Still, removing carbon from the air remains difficult, and as with all early-stage lab-scale studies, the challenge is scaling up the system for pilot studies. The concentration of carbon dioxide, though it is increasing, now stands at about 400 parts per million, or 0.04%. That means that any technology to capture the gas from the air requires moving huge volumes of air – and that requires large electricity consumption for running fans, says Kazemifar. “I believe the high energy intensity of the process is the main challenge with all [direct air capture] technologies.”

Having to heat this material to just 120 F (49 C) means it will use far less energy than other substances/techniques.  That amount of heat can be produced simply by sunshine with the help of mirrors or lenses.  The air in a sealed car will reach 120F in half an hour when the air outside is just 80F.  The stuff can be reused at least 100 times.  In other words, direct air capture (DAC) will become much, much cheaper.   The second half of "carbon capture and storage" is the storage.  In this piece, which I wrote in 2016, I discuss converting CO2 to rock, by dissolving it in water and injecting it into 
basaltic rock, which is full of air holes.  Within 2 years, the holes fill with a stable chalky rock, which has been made from the CO2.  Basalt is fairly widespread across the globe.  In other words, as soon as this product is commercialised, we will be able to extract CO2 from the atmosphere and safely store it underground at low cost.  In fact, with luck, the European price on carbon, currently about US$70/tonne, might be enough to cover the costs.

Something to be hopeful about.

Carbon-neutral jetfuel

 

From RenewEconomy

British synthetic fuels developer Zero Petroleum is exploring the possibility of building a low-carbon sustainable aviation fuel production facility in the South Australian city of Whyalla, in collaboration with Qantas Airways.

The feasibility study is expected to take six months and will evaluate the technical, economic, and environmental viability of a facility which would be capable of producing up to 10 million litres of synthetic aviation fuel, gasoline, and diesel each year.

It will seek to tap into the state’s huge wind and solar resources – which already account for around 75 per cent of annual demand, and which are expected to reach 100 per cent net renewables by 2027 – and its emerging green hydrogen production facilities in the same city.

Zero Petroleum was founded in 2020 by former F1 racing engineer and executive Paddy Lowe and subject expert Nilay Shah, a professor of process systems engineering at Imperial College London.

Their company has developed and manufactures whole-blend and 100% fossil free synthetic fuels – including gasoline, diesel, and jet fuel – through a process utilising direct air capture (DAC) carbon dioxide and hydrogen from water electrolysis, all powered by renewable energy.

This is designed to create fuels which are intended for use in an array of hard-to-abate sectors – including the aviation industry and motor racing series such as Formula 1.

DAC is the process whereby CO2 is extracted from the atmosphere.  DAC is expensive, costing over $1000/tonne, although as its usage increases, and learning curve effects strengthen, it is likely to fall in cost.   DAC may be the right way to go for removing CO2 from the atmosphere, but it is prolly not the best way to make synthetic hydrocarbons.  The process used by Prometheus Fuels will (if it works) be much cheaper.  We are just at the beginning of learning how to make carbon-neutral fuels, so it makes sense to try several technological possibilities, to see which works best and which is the cheapest.  We shall see which process wins out.

Making hydrogen electrolysers super efficient

The traditional electrolysis process is relatively inefficient.   If you use surplus green electricity to produce hydrogen and then burn the hydrogen to make electricity, its round-trip efficiency is low, much lower than alternative energy storage techniques:

 

Flora noted that converting power to hydrogen and then using the fuel to generate power has a relatively low round-trip efficiency. Round-trip efficiency is the percentage of electricity retrieved after being stored.

The technology to convert power to hydrogen and back to power has a round-trip efficiency of 18%-46%, according to data that Flora presented from the Massachusetts Institute of Technology and scientific journal Nature Energy. In comparison, two mature long-duration technologies, pumped-storage hydropower and compressed air energy storage, boast round-trip efficiencies of 70%-85% and 42%-67%, respectively. Flow batteries, a rechargeable fuel cell technology that is less mature, have a round-trip efficiency of 60%-80%. 

(Source: S&P Global --- Hydrogen technology faces efficiency disadvantage in power storage race
)

[Incidentally, Elon Musk claims that's Tesla's lithium-ion batteries have a round-trip efficiency of 93%]

But an Australian start-up, Hysata, is developing a process which enormously increases the efficiency of electrolysis.    I've already talked about this company and their super efficient hydrogen electrolyser, here.  

This update is from ARENA (Australian Renewable Energy Agency)

A pioneering, all-Australian hydrogen electrolyser technology is getting the chance to prove itself at a commercial scale.

If it works, the project has the potential to transform the economics of renewable hydrogen production.

ARENA’s support has helped develop this new technology since it was a concept in a University of Wollongong laboratory. That work saw a spin-off company, Hysata, established to commercialise the development.

Now, Hysata will receive $20.9 million ARENA funding as part of a $47.5 million project. Hysata will build and test a 5 MW system at its new Port Kembla manufacturing facility.

The plan then is to move the entire system to Rockhampton in Queensland, for installation and trials next to the Stanwell Power Station.

Queensland government-owned power company Stanwell Corporation is providing the site and facilities, and also backing the project with $3 million.

ARENA CEO Darren Miller says the project is a crucial step to enabling purchase orders for the technology.

“Hysata’s electrolyser technology could be a game-changer for renewable hydrogen,” Mr Miller said.

“The demonstration at Stanwell’s site will be key to unlocking commercial demand for Hysata’s product by proving the technology works at scale.

Currently, the production cost of renewable hydrogen (using renewable energy) is at least twice that of hydrogen produced from fossil fuels. Hysata says its technology will slash costs and produce hydrogen “well below” a competitive target price of $2 per kilogram (approx. US$1.50/kg).

FYI, if there’s one number you should remember, it is that price of $2 per kilogram. That’s the key to competing with fossil fuel-derived hydrogen and fully unlocking renewable hydrogen’s industrial and energy future.

It’s all in the bubbles.   All electrolysers work by passing an electric current from electrodes through H2O – water. The current splits the water into its two parts, hydrogen and oxygen. That process takes energy.

Now, if the entire process were 100 per cent efficient, all that energy would go into splitting the water. Nothing else.

But, until now, electrolysers have also produced a lot of heat. That’s because, just like an electric heater at home, they have electrical resistance.

The heat generated is not only wasted energy, but it must also be removed. Electrolysers need a lot of cooling and that uses even more energy.

So, if you can reduce resistance, a greater proportion of energy is available to split the water. Also, the system generates far less far less heat, which in turn requires less cooling.

Hysata has tackled the problem by completely redesigning their electrolyser to remove all the main sources of electrical resistance.

It turns out, that means eliminating hydrogen and oxygen bubbles. When bubbles form on the electrolyser’s electrodes, they reduce the surface area available for electrolysis and increase resistance.

In fact, Hysata says it has completely eliminated bubbles from its system and cut electrical resistance to virtually zero. As a result, Hysata says it expects a fully operational electrolyser will stay cool through good air ventilation alone.

The combined effect is what has raised the overall efficiency of a Hysata electrolyser to around 95 per cent. That’s a huge jump on current technologies, which operate with efficiencies closer to 75 per cent.

To put that in context, to make renewable hydrogen competitive with its fossil-fuel derived alternative, the International Renewable Energy Agency (IRENA) in 2020 set an electrolyser efficiency target of up to 85 per cent … by 2050.

I'm not sure that hydrogen by itself is in fact the future.   To transport it, you need to compress it and refrigerate it, which takes additional energy, further reducing its round-trip efficiency.  Also, it makes gas pipes brittle, and, because its molecules are so small, it easily escapes through the gaps in the molecular lattices of gas pipes or storage tanks.   But if you convert it to methane, using the Sabatier process, it's the equivalent of natural gas, and in fact is called synthetic natural gas (SNG, which is a bit of an oxymoron, no?)  And then you can use the existing gas distribution system and gas storage system, as well as existing gas turbine electricity generators.  On the other hand, to make SNG, you need a source of CO2, and unless you use the escape gases from a gas-turbine power plant flue, you have to produce CO2 using direct air capture, which is still very expensive.

We will need seasonal (or long-term storage)  to reach 100% renewables, and hydrogen, or more probably, SNG, will be how we fill that gap.  So, if this can be commercialised, it will be a huge step forwards towards a 100% green energy system. 

We're going to miss 1.5 degrees

From The BBC

A leading British climate scientist has told the BBC he believes the target to limit global warming to 1.5C will be missed.  Professor Sir Bob Watson, former head of the UN climate body, told the BBC's Today programme he was "pessimistic".  His warning comes amidst a summer of extreme heat for Europe, China and the US.

The UN says passing the limit will expose millions more people to potentially devastating climate events.

The world agreed to try to limit the temperature increase due to climate change to 1.5C above pre-industrial levels at a UN conference in Paris in 2015. That target has become the centrepiece of global efforts to tackle climate change.

Climate scientists have been warning governments for years that they are not cutting their countries' emissions quickly enough to keep within this target.

But it is surprising for someone as senior and well respected as the former head of the UN climate science body the IPCC to be so frank that he believes it will be missed.

Professor Sir Bob Watson is currently Emeritus Professor of the UK's Tyndall Centre for Climate Research - having previously worked at the UN, Nasa, UK's Department of Environment and the US White House - and is perhaps one of the foremost climate scientists in the world.

In the interview aired on Thursday he said: "I think most people fear that if we give up on the 1.5 [Celsius limit] which I do not believe we will achieve, in fact I'm very pessimistic about achieving even 2C, that if we allow the target to become looser and looser, higher and higher, governments will do even less in the future."

His comments although candid were supported by Lord Stern, Chairman of the Grantham Research Institute on Climate Change and the Environment, later on Thursday during an interview with BBC's WATO programme.

He said: "I think 1.5 is probably out of reach even if we accelerate quickly now, but we could bring it back if we start to bring down the cost of negative emissions and get better at negative emissions. Negative emissions means direct air capture of carbon dioxide."  [Except that direct air capture (DAC) is very expensive]

Based on current government commitments to cutting greenhouse gas emissions, Climate Action Tracker predicts that global temperatures will rise to 2.7C.

The figure is not a direct measure of the world's temperature but an indicator of how much or how little the Earth has warmed or cooled compared to the long-term global average - and even slight changes can have significant impacts.

The UN climate body, the IPCC, has said keeping temperature rises below 1.5C, rather than 2C, would mean:

• 10 million fewer people would lose their homes to rising sea levels
• a 50% reduction in the number of people experiencing water insecurity
• a reduction in coral reef loss from 99% to 70%

Prof Sir Bob Watson said that the world was struggling to prevent temperature rises as we are not reducing emissions fast enough.

"The big issue is we need to reduce greenhouse gases now to even be on the pathway to be close to 1.5C or 2C. We need to reduce current emissions by at least 50% by 2030. The trouble is the emissions are still going up, they are not going down," he said.

He told the Today programme that setting targets was not enough and countries needed to back these up with action: "We need to try and hold governments to start to act sensibly now and reduce emissions, but even governments with a really good target like the United Kingdom don't have the policies in place, don't have the financing in place to reach those goals."

In March the UK's watchdog on climate change, the UKCCC, said the UK had lost its leadership on climate issues. It said the government's backing of new oil and coal projects, airport expansion plans and slow progress on heat pumps showed a lack of urgency.

Note how the 1.5 degrees pathway requires carbon capture after 2070 to reach that goal.
Given its cost, that seems unlikely,
 since people today object to paying a few cents more for electricity

 

Removing 1 million tons of carbon a year

From Interesting Engineering

Carbon capture technologies have great potential for helping in the fight against climate change, and big names such as Bill Gates and Elon Musk are showing their faith in the technology by investing in new solutions.

Now, the world looks set for a breakthrough moment in carbon capture technologies, with a new facility set to open in Scotland that will remove up to one million tons of carbon [dioxide] from the air each year, a press statement reveals.

The direct air capture (DAC) facility will be built by UK energy transition company Storegga Geotechnologies in collaboration with the Canadian carbon capture technology firm Carbon Engineering.

The facility, which will be the largest in the world, will extract the equivalent carbon (one million tons) that would be absorbed by 40 million trees over the course of a year. All of the absorbed carbon will then be deposited in storage sites under the sea.

The facility will feature large fans that pull air into a liquid-filled vat that binds the carbon dioxide. Once bound, the captured carbon is refined and transformed into calcium carbonate pellets.

These pellets, in turn, are heated and decompose into a CO2 stream alongside calcium oxide. This stream is then cleaned of impurities, after which it is pumped into an undersea storage site.

The new facility joins a host of other carbon capture technology innovations aimed at meeting the requirement of reducing the amount of CO2 in the atmosphere if we are to reverse the adverse effects of climate change.

As the Union of Concerned Scientists (UCS) points out on its website, "to reach net-zero emissions, we need to do more than just reduce our emissions: we need to actively remove carbon dioxide from the atmosphere or offset its effects."

Another new system, the Bill Gates-backed Carbfix, will extract carbon from the atmosphere and turn it into rocks. One devised by UCLA scientists, meanwhile, takes inspiration from seashells to extract carbon from the ocean, which would, in turn, absorb more out of the air.

While the Scottish facility from Storegga Geotechnologies and Carbon Engineering will mainly be aimed at removing carbon dioxide from the atmosphere, both firms do say they want to eventually sell carbon dioxide collected from their plants.

The two companies are currently seeking a site location for their new facility in the country of Scotland, which was chosen due to the fact that a large number of its labor force is already trained in the skills needed for such projects — renewable energy met over 97 percent of the country's energy demands in 2020.

In their statement, Carbon Engineering says both partners aim for the facility to be operational by 2026.

Sounds good, doesn't it?  But there are a few problems.  First, although a million tonnes a year seems a lot,  China's and the USA's annual emissions total 15 billion tonnes of CO2 a year, about 40% of global emissions.  We would need 15,000 of these plants just to offset the emissions of these countries.  Still, if we put our minds to it, and our shoulders to the wheel, etc., etc., we could in principle achieve that.  

However, that's not the only problem.  To permanently store the CO2, we need to either put it into caverns where it can never escape, otherwise it'll just go straight back into the atmosphere; or convert it to rock by dissolving it in water and pumping it into basalt.  In the manufacturing process, calcium carbonate (i.e., limestone) is produced, which could simply be dumped into the sea, but the calcium needed for this is produced by energy-intensive methods, either electrolysis or by reducing lime at high temperatures. 

Also, these guys are also going to be selling their carbon dioxide.  Which means it's not being withdrawn from the atmosphere.  I understand it's a startup, and they may need temporary expedients to help it survive until the carbon price is high enough to make direct air capture of CO2 profitable.  All the same.

The best way to slash net emissions is to replace coal power stations with wind and solar and other renewables, and to replace ICEVs with EVs or PHEVs.  But carbon capture and storage(CCS) will be needed, if only to reverse the emissions of cement production and air travel, together (depending on your data source) around 10% of global emissions.  These sectors will need to pay a carbon tax to fund this and other CCS schemes.  And if we need to offset just these sectors, the number of CCS plants needed will be much fewer.

So, not as big a step forward as the article is trying to make out, but still worthwhile.

De-carbonisation via carbon capture is a mirage

From The Conversation.

Collectively we three authors of this article must have spent more than 80 years thinking about climate change. Why has it taken us so long to speak out about the obvious dangers of the concept of net zero? In our defence, the premise of net zero is deceptively simple – and we admit that it deceived us.

The threats of climate change are the direct result of there being too much carbon dioxide in the atmosphere. So it follows that we must stop emitting more and even remove some of it. This idea is central to the world’s current plan to avoid catastrophe. In fact, there are many suggestions as to how to actually do this, from mass tree planting, to high tech direct air capture devices that suck out carbon dioxide from the air.

The current consensus is that if we deploy these and other so-called “carbon dioxide removal” techniques at the same time as reducing our burning of fossil fuels, we can more rapidly halt global warming. Hopefully around the middle of this century we will achieve “net zero”. This is the point at which any residual emissions of greenhouse gases are balanced by technologies removing them from the atmosphere.

This is a great idea, in principle. Unfortunately, in practice it helps perpetuate a belief in technological salvation and diminishes the sense of urgency surrounding the need to curb emissions now.

We have arrived at the painful realisation that the idea of net zero has licensed a recklessly cavalier “burn now, pay later” approach which has seen carbon emissions continue to soar. It has also hastened the destruction of the natural world by increasing deforestation today, and greatly increases the risk of further devastation in the future.

 

To understand how this has happened, how humanity has gambled its civilisation on no more than promises of future solutions, we must return to the late 1980s, when climate change broke out onto the international stage.

On June 22 1988, James Hansen was the administrator of Nasa’s Goddard Institute for Space Studies, a prestigious appointment but someone largely unknown outside of academia.

By the afternoon of the 23rd he was well on the way to becoming the world’s most famous climate scientist. This was as a direct result of his testimony to the US congress, when he forensically presented the evidence that the Earth’s climate was warming and that humans were the primary cause: “The greenhouse effect has been detected, and it is changing our climate now.”

If we had acted on Hansen’s testimony at the time, we would have been able to decarbonise our societies at a rate of around 2% a year in order to give us about a two-in-three chance of limiting warming to no more than 1.5°C. It would have been a huge challenge, but the main task at that time would have been to simply stop the accelerating use of fossil fuels while fairly sharing out future emissions.

Four years later, there were glimmers of hope that this would be possible. During the 1992 Earth Summit in Rio, all nations agreed to stabilise concentrations of greenhouse gases to ensure that they did not produce dangerous interference with the climate. The 1997 Kyoto Summit attempted to start to put that goal into practice. But as the years passed, the initial task of keeping us safe became increasingly harder given the continual increase in fossil fuel use.

It was around that time that the first computer models linking greenhouse gas emissions to impacts on different sectors of the economy were developed. These hybrid climate-economic models are known as Integrated Assessment Models. They allowed modellers to link economic activity to the climate by, for example, exploring how changes in investments and technology could lead to changes in greenhouse gas emissions.

They seemed like a miracle: you could try out policies on a computer screen before implementing them, saving humanity costly experimentation. They rapidly emerged to become key guidance for climate policy. A primacy they maintain to this day.

Unfortunately, they also removed the need for deep critical thinking. Such models represent society as a web of idealised, emotionless buyers and sellers and thus ignore complex social and political realities, or even the impacts of climate change itself. Their implicit promise is that market-based approaches will always work. This meant that discussions about policies were limited to those most convenient to politicians: incremental changes to legislation and taxes.

Around the time they were first developed, efforts were being made to secure US action on the climate by allowing it to count carbon sinks of the country’s forests. The US argued that if it managed its forests well, it would be able to store a large amount of carbon in trees and soil which should be subtracted from its obligations to limit the burning of coal, oil and gas. In the end, the US largely got its way. Ironically, the concessions were all in vain, since the US senate never ratified the agreement.


Postulating a future with more trees could in effect offset the burning of coal, oil and gas now. As models could easily churn out numbers that saw atmospheric carbon dioxide go as low as one wanted, ever more sophisticated scenarios could be explored which reduced the perceived urgency to reduce fossil fuel use. By including carbon sinks in climate-economic models, a Pandora’s box had been opened.

It’s here we find the genesis of today’s net zero policies.

That said, most attention in the mid-1990s was focused on increasing energy efficiency and energy switching (such as the UK’s move from coal to gas) and the potential of nuclear energy to deliver large amounts of carbon-free electricity. The hope was that such innovations would quickly reverse increases in fossil fuel emissions.

But by around the turn of the new millennium it was clear that such hopes were unfounded. Given their core assumption of incremental change, it was becoming more and more difficult for economic-climate models to find viable pathways to avoid dangerous climate change. In response, the models began to include more and more examples of carbon capture and storage, a technology that could remove the carbon dioxide from coal-fired power stations and then store the captured carbon deep underground indefinitely.

This had been shown to be possible in principle: compressed carbon dioxide had been separated from fossil gas and then injected underground in a number of projects since the 1970s. These Enhanced Oil Recovery schemes were designed to force gases into oil wells in order to push oil towards drilling rigs and so allow more to be recovered – oil that would later be burnt, releasing even more carbon dioxide into the atmosphere.

Carbon capture and storage offered the twist that instead of using the carbon dioxide to extract more oil, the gas would instead be left underground and removed from the atmosphere. This promised breakthrough technology would allow climate friendly coal and so the continued use of this fossil fuel. But long before the world would witness any such schemes, the hypothetical process had been included in climate-economic models. In the end, the mere prospect of carbon capture and storage gave policy makers a way out of making the much needed cuts to greenhouse gas emissions.

When the international climate change community convened in Copenhagen in 2009 it was clear that carbon capture and storage was not going to be sufficient for two reasons.

First, it still did not exist. There were no carbon capture and storage facilities in operation on any coal fired power station and no prospect the technology was going to have any impact on rising emissions from increased coal use in the foreseeable future.

The biggest barrier to implementation was essentially cost. The motivation to burn vast amounts of coal is to generate relatively cheap electricity. Retrofitting carbon scrubbers on existing power stations, building the infrastructure to pipe captured carbon, and developing suitable geological storage sites required huge sums of money. Consequently the only application of carbon capture in actual operation then – and now – is to use the trapped gas in enhanced oil recovery schemes. Beyond a single demonstrator, there has never been any capture of carbon dioxide from a coal fired power station chimney with that captured carbon then being stored underground.

Just as important, by 2009 it was becoming increasingly clear that it would not be possible to make even the gradual reductions that policy makers demanded. That was the case even if carbon capture and storage was up and running. The amount of carbon dioxide that was being pumped into the air each year meant humanity was rapidly running out of time.

 

With hopes for a solution to the climate crisis fading again, another magic bullet was required. A technology was needed not only to slow down the increasing concentrations of carbon dioxide in the atmosphere, but actually reverse it. In response, the climate-economic modelling community – already able to include plant-based carbon sinks and geological carbon storage in their models – increasingly adopted the “solution” of combining the two.

So it was that Bioenergy Carbon Capture and Storage, or BECCS, rapidly emerged as the new saviour technology. By burning “replaceable” biomass such as wood, crops, and agricultural waste instead of coal in power stations, and then capturing the carbon dioxide from the power station chimney and storing it underground, BECCS could produce electricity at the same time as removing carbon dioxide from the atmosphere. That’s because as biomass such as trees grow, they suck in carbon dioxide from the atmosphere. By planting trees and other bioenergy crops and storing carbon dioxide released when they are burnt, more carbon could be removed from the atmosphere.

With this new solution in hand the international community regrouped from repeated failures to mount another attempt at reining in our dangerous interference with the climate. The scene was set for the crucial 2015 climate conference in Paris.

As its general secretary brought the 21st United Nations conference on climate change to an end, a great roar issued from the crowd. People leaped to their feet, strangers embraced, tears welled up in eyes bloodshot from lack of sleep.

The emotions on display on December 13, 2015 were not just for the cameras. After weeks of gruelling high-level negotiations in Paris a breakthrough had finally been achieved. Against all expectations, after decades of false starts and failures, the international community had finally agreed to do what it took to limit global warming to well below 2°C, preferably to 1.5°C, compared to pre-industrial levels.

The Paris Agreement was a stunning victory for those most at risk from climate change. Rich industrialised nations will be increasingly impacted as global temperatures rise. But it’s the low lying island states such as the Maldives and the Marshall Islands that are at imminent existential risk. As a later UN special report made clear, if the Paris Agreement was unable to limit global warming to 1.5°C, the number of lives lost to more intense storms, fires, heatwaves, famines and floods would significantly increase.

But dig a little deeper and you could find another emotion lurking within delegates on December 13. Doubt. We struggle to name any climate scientist who at that time thought the Paris Agreement was feasible. We have since been told by some scientists that the Paris Agreement was “of course important for climate justice but unworkable” and “a complete shock, no one thought limiting to 1.5°C was possible”. Rather than being able to limit warming to 1.5°C, a senior academic involved in the IPCC concluded we were heading beyond 3°C by the end of this century.

Instead of confront our doubts, we scientists decided to construct ever more elaborate fantasy worlds in which we would be safe. The price to pay for our cowardice: having to keep our mouths shut about the ever growing absurdity of the required planetary-scale carbon dioxide removal.

Taking centre stage was BECCS because at the time this was the only way climate-economic models could find scenarios that would be consistent with the Paris Agreement. Rather than stabilise, global emissions of carbon dioxide had increased some 60% since 1992.

Alas, BECCS, just like all the previous solutions, was too good to be true.

Across the scenarios produced by the Intergovernmental Panel on Climate Change (IPCC) with a 66% or better chance of limiting temperature increase to 1.5°C, BECCS would need to remove 12 billion tonnes of carbon dioxide each year. BECCS at this scale would require massive planting schemes for trees and bioenergy crops.

The Earth certainly needs more trees. Humanity has cut down some three trillion since we first started farming some 13,000 years ago. But rather than allow ecosystems to recover from human impacts and forests to regrow, BECCS generally refers to dedicated industrial-scale plantations regularly harvested for bioenergy rather than carbon stored away in forest trunks, roots and soils.

Currently, the two most efficient biofuels are sugarcane for bioethanol and palm oil for biodiesel – both grown in the tropics. Endless rows of such fast growing monoculture trees or other bioenergy crops harvested at frequent intervals devastate biodiversity.

It has been estimated that BECCS would demand between 0.4 and 1.2 billion hectares of land. That’s 25% to 80% of all the land currently under cultivation. How will that be achieved at the same time as feeding 8-10 billion people around the middle of the century or without destroying native vegetation and biodiversity?


Growing billions of trees would consume vast amounts of water – in some places where people are already thirsty. Increasing forest cover in higher latitudes can have an overall warming effect because replacing grassland or fields with forests means the land surface becomes darker. This darker land absorbs more energy from the Sun and so temperatures rise. Focusing on developing vast plantations in poorer tropical nations comes with real risks of people being driven off their lands.

And it is often forgotten that trees and the land in general already soak up and store away vast amounts of carbon through what is called the natural terrestrial carbon sink. Interfering with it could both disrupt the sink and lead to double accounting.

As these impacts are becoming better understood, the sense of optimism around BECCS has diminished.

Given the dawning realisation of how difficult Paris would be in the light of ever rising emissions and limited potential of BECCS, a new buzzword emerged in policy circles: the “overshoot scenario”. Temperatures would be allowed to go beyond 1.5°C in the near term, but then be brought down with a range of carbon dioxide removal by the end of the century. This means that net zero actually means carbon negative. Within a few decades, we will need to transform our civilisation from one that currently pumps out 40 billion tons of carbon dioxide into the atmosphere each year, to one that produces a net removal of tens of billions.

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There is only one plausible way to cut CO2 and methane emissions.  And that's to actually cut them.  Offsets won't work.  Negative emissions won't work.  BECCS won't work.  It's no wonder emissions continue to rise.  We are heading towards a 3° C rise, not 1.5°.  And that will be catastrophic for our civilisation, the world's people and the environment.