Climate scientist Dr Andrew Lenton spends a lot of time thinking about how to permanently remove atmospheric carbon dioxide.
As Director of our CarbonLock Future Science Platform he’s exploring new technologies in biology, chemistry and engineering to remove carbon dioxide from the atmosphere.
We talked to him ahead of this year’s United Nations Climate Change Conference (COP28) about his work in the emerging field of carbon dioxide removal.
You work in an area of science called ‘carbon dioxide removal’. What’s it about?
Carbon dioxide removal is about actively removing carbon dioxide from the atmosphere. Once it’s been removed, it needs to be stored away, ideally for long periods, to avoid it being re-released.
We need to do this for three reasons. First, we can’t limit the global temperature rise to 1.5 degrees without it. Globally, we’re continuing to emit around 40 gigatonnes of CO₂ into the atmosphere every year. This amount is increasing. That means there’s a lot of carbon dioxide remaining in the atmosphere.
Second, for some industries, it will be much harder to reduce emissions than others. So carbon dioxide removal will need to ‘offset’ what is otherwise difficult to eliminate completely.
Third, even once net zero is reached, we still need to address the legacy of hundreds of years of carbon dioxide emissions that remain in our atmosphere.
The remaining amount of carbon dioxide we can safely emit to limit warming to 1.5 degrees is rapidly depleting. To reach net zero, we’ll need to address historic and future atmospheric carbon dioxide emissions. The only way to do that is through emissions removal.
How important are carbon dioxide removal technologies in getting to net zero?
Let’s be clear from the outset. Emissions removal is no substitute for emissions reductions. There is a huge amount of work to be done to get to net zero. We will need to reduce greenhouse gas emissions as fast as we can if we are to limit the damage of rising global temperatures.
The lack of action – over many decades – to limit atmospheric carbon dioxide emissions means we now need both deep emissions cuts and carbon dioxide removal to be able to achieve net zero.
Without carbon dioxide removal (CDR), we will not reach net zero emissions; this is an irrefutable fact. We will have carbon dioxide remaining in our atmosphere that will mean the global atmospheric temperature will continue to increase.
Almost every road to reach net zero emissions will require CDR. We are on an emissions trajectory that is largely incompatible with limiting temperature rise to 1.5 degrees.
The latest Intergovernmental Panel on Climate Change (IPCC) report underscored that CDR is now necessary to achieve net zero, even under the most ambitious scenario for emissions reductions. So, it’s fundamental that we develop carbon dioxide removal technologies as fast as we can.
How soon will we need to deploy them?
If we are to prevent serious climate risks associated with higher warming levels, we will need carbon dioxide removal technologies to be deployed at scale and well before the middle of the century.
The key challenge is the technologies to enable carbon dioxide removal at the scales required don’t exist yet.
By carbon dioxide removal, do you mean carbon capture and storage?
No, it’s very different. Carbon capture and storage (CCS) is aimed at preventing more emissions at point of source when extracting fossil fuels, for example, at gas or coal power plants. This is what is called ‘avoided emissions’ rather than ‘emissions removals’. CCS can’t actually draw down atmospheric carbon dioxide levels.
The bulk of the work to be done in tackling climate change is through emission reductions, primarily across the energy sector, but involving all sectors, like industry, buildings, and agriculture. Where we can’t switch to renewables for energy sources straight away, CCS will play a role in preventing emissions being lost to the atmosphere. So, while they sound very similar, these technologies play quite different roles in climate mitigation.
Can CCS equipment and processes be used in carbon dioxide removal?
Yes, and this is where it gets complex. CCS is an enabling technology of CDR. By that I mean – when you take the carbon out of the atmosphere, you need to find a way to capture and store it. CCS faces its own barriers to deployment, including working at scale and securing investment, and economic competitiveness. CCS, when used for CDR, would need to be used with other technologies, like direct air capture.
CDR goes beyond just CCS and direct air capture, and is looking at solutions spanning biology, chemistry, and engineering. One of the more promising CDR technologies is mineralisation or rock weathering, but we are exploring a portfolio of solutions.
So, carbon dioxide removal, in addition to emissions reductions, is part of a range of things we can do that make up the ‘net’ in net zero emissions. Of course, there is a lot of socio-economic work to be done around how, internationally, carbon dioxide removal offsets would work. And there’s a big task ahead for governments to align their CDR ambitions and ensure the right governance is in place to ensure CDR isn’t used in the place of emissions reductions.
Let’s unpack the ‘why’ in carbon dioxide removal. How can carbon dioxide be used to ‘offset’ hard to abate emissions?
It’s easiest to think about it by ‘balancing the equation’. We’ve established that reaching net zero will require both emissions reductions and emissions removals. So we need to take concerted steps to limit what is released into the atmosphere in parallel to actively taking carbon dioxide out.
But each sector faces different challenges in limiting emissions on the pathway to net zero. Assuming governments can implement emissions reductions policies - and there is widespread uptake by businesses and communities - even then, some emissions will be difficult and slow to eliminate.
Think of them as ‘residual’ emissions, once we have exhausted all options to reduce them completely. In the meantime, we need to do everything we can to drive emissions down.
Doesn’t nature already play a role in removing carbon dioxide from the atmosphere?
Nature-based solutions, such as trees, provide important environmental benefits, including carbon sequestration. But it’s not on a scale large enough to reach the level of atmospheric removal needed to limit warming and reduce atmospheric carbon dioxide concentrations. In many cases, they can’t offer permanent storage benefits. There are challenges around fire, droughts, and other extreme events impacting nature-based solutions.
The guiding principle of the program of work I lead in CDR at CarbonLock is to 'develop technologies that let us take the carbon dioxide out once and keep it out permanently’.
How much carbon do we need to permanently take out of the atmosphere?
The current global estimate is somewhere between 4.7 and 10 gigatonnes of carbon dioxide removal is needed to be captured and stored annually by 2050, rising to double that by 2100.
The amount of carbon needed to be removed from the atmosphere is initially very small in comparison to what we actively need to reduce. I cannot emphasise enough that we must exhaust all options to get to the point of net zero by limiting what we put into the atmosphere in the first place. It’s much more difficult to bring it in than it is to put it out.
Likewise, CDR alone will never be the whole solution to reaching net zero emissions. But together with deep cuts in emissions, it offers a pathway to net zero emissions and onto a net negative world.
That’s where we start to remove more carbon dioxide from the atmosphere than we emit, gradually lowering atmospheric carbon dioxide concentrations.
Hold on, net negative?
So, net zero means removing as much carbon dioxide that is being released into the atmosphere, and removing what is hard-to-abate.
In the Paris Agreement, we signed onto net negative emissions, so reaching net zero is only the first step. Taking more out than is being released – net negative emissions – is where we need to be.
This means once net zero emissions are reached, we will need to go one step further – by removing carbon dioxide in an attempt to bring temperatures back down to 1.5 degrees again. Net negative emissions is the only way we can begin to reverse the damage of climate change.
We need to try and increase understanding of net negative in Australia. Net zero is only 30 years away, but net negative means we will need to be deploying CDR well beyond this century. We’re going to need whole new industries and frameworks to support these technologies. So there’s a huge opportunity to reinvent existing and create new industries for Australia.
There is consensus we are on the cusp of passing 1.5 degrees Celsius of warming in the next decade, and two degrees is fast approaching. What are the implications for CDR?
That’s a great question. My research background is in studying the impact of climate change on the ocean. I recently collaborated on a paper around the overshoot of climate targets. We found this would have grave consequences for the world’s oceans and the ecosystems they support. There is a general assumption the climate system is reversible, and that’s not the case. Our recent analysis found under an overshoot scenario, associated changes in water temperatures and oxygen levels will decrease viable ocean habitats for centuries.
Put simply, the more successfully we can rapidly decarbonise, the less work there is for CDR to do, both in the lead-up to net zero and beyond.
What is CSIRO’s CarbonLock Future Science Platform up to?
I lead a team developing novel carbon dioxide removal technologies to help us reach net zero and onto net negative emissions. According to a recent report on sequestration potential released by the Climate Change Authority, Australia has a strong value proposition to tackle carbon dioxide removal because we have the right minerals, vast marine estate, and abundant renewable resources needed for the sequestration process.
The goal of the CarbonLock Future Science Platform is to develop permanent atmospheric carbon removal. We’ve currently got more than 90 people involved in CarbonLock and we’re working on more than 18 projects.
Our CarbonLock Future Science Platform is part of a global network called Mission Innovation, which seeks to achieve a net reduction of 100 million tonnes of carbon dioxide per year, globally by 2030. That’s already a huge amount of carbon dioxide, and an important step, but we need to do even more.
What have you found so far?
The ocean is one of the largest stores of carbon dioxide, and our team is examining ocean-based approaches that permanently remove atmospheric carbon dioxide. By adding alkalinity - for example, through the addition of lime - we can induce an additional uptake of carbon dioxide to the ocean.
Another way of storing atmospheric carbon dioxide over long timescales is a process that involves reacting it with rocks, otherwise known as mineral carbonation. But there’s a long way to go in terms of identifying which types of minerals have the highest potential to achieve carbonation at scale. As well as learning how to accelerate what is a very slow, naturally occurring geological process.
As a climate scientist by trade, how did you find yourself in this field of work?
I was drawn to work on carbon dioxide removal as it deals with the root problem of climate change - rising atmospheric carbon dioxide levels - rather than just the warming alone. My work has evolved from understanding the impacts of climate change on the climate system, such as ocean acidification, to exploring what we can do to avoid the worst impacts of climate change.
One of the most exciting things about CDR is we're not just taking notes here as the ship sinks, if you will. We're actively developing new science, new ideas, bringing new people into the fold here, really trying to develop solutions that will guide us to net zero and ultimately on to net negative emissions.
How important will CDR discussions be at COP28?
Carbon dioxide removal will be important in negotiations and outcomes at COP28. I am keen to highlight the work Australia and CSIRO are doing in Mission Innovation and to meet with colleagues and strengthen and build international relationships needed to develop and deploy CDR at scale.