Earth's carbon storage capability 10% of previous estimates

Climate scientists say that Earth may be able to sequester far less carbon than current models assume. The findings - which have been published in Nature - suggest our planet’s long-term carbon storage capacity is - realistically - maybe only a tenth of what we thought we might be able to lay our hands on. This matters, because, if part of our strategy to combat climate change relies on sequestering at least a proportion of the carbon dioxide we emit, that rescue package just shrank by 90%. Joeri Rogelj authored the study; he is at Imperial College London…

Joeri - So we know that climate change is happening and we know very well what we need to do to stop that from becoming worse. And that is we need to stop adding carbon dioxide to the atmosphere. Now, there is a variety of ways in which we can reduce the amount of carbon dioxide that we emit. The most important way is, of course, to stop producing carbon dioxide by stop burning fossil fuels. But another additional way of doing this is to capture CO2, carbon dioxide, and to pump it underground. And the estimates of how much of that carbon dioxide we could be pumping underground until recently were really enormous. Tens of thousands of billion tonnes of carbon dioxide. And what we are trying to do with this study is to see whether all of this technical potential is actually practically available. If we take into account some aspects like where it could be risky or where it would be undesirable to actually be pumping CO2 underground.

Chris - So you're saying, ignoring the practicalities for a minute, assuming we could do this and we capture carbon dioxide and we wanted to, and we were going to put it underground, how much could we really put underground compared to what people think we could, is sort of where you were coming from?

Joeri - Exactly. So we very much rely on what people have done before. So what we do is not starting from a fundamentally different point. We start from this technical potential of how much space there is underground in our Earth's crust to store carbon dioxide. But then we start removing those areas where we think the risk is too high. For example, we start removing those areas that are too close to where people live. Because pumping things underground means that there is a risk that this carbon dioxide starts to seep into the groundwater and so on. We also exclude areas that are currently protected. We exclude areas that are too deep or areas that are too deep in the ocean. Or equally, we look at areas that maybe might be managed by indigenous groups and where we therefore do not want to disturb nature or the environment. And if we start doing that, we start to see that lots of the technical, physical potential that is available starts to be excluded. And we ended up with an estimate that is significantly smaller than the hypothetical global estimate for storage that would be available.

Chris - What does your number look like then? And how does it compare with what we thought we had at our disposal?

Joeri - The number is still big, 1460 billion tonnes of CO2. So just to put this in context, right now, on an annual basis, our entire global economy is emitting 40 billion tonnes of CO2 into the atmosphere. It would take more than 30 years of current global emissions to reach this entire 1400 billion tonnes.

The important thing, however, is that this is almost a factor 10 smaller than our starting estimate, that does not take into account these different risk factors or areas where we would not necessarily want to be pumping CO2 in the ground.

Chris - Another way of looking at it is to say, well, how much climate change in terms of temperature escalation does that offset? And for how long?

Joeri - Yeah, that's right. So every ton that we emit in the atmosphere adds to global warming. We also understand that if we remove carbon dioxide from the atmosphere and then permanently store it somewhere so that it doesn't enter the air anymore, then global warming will be reversing. There are some uncertainties around this, but to first order, we understand that this will happen. And so we can estimate what removing 1460 billion tonnes of carbon dioxide means in terms of reversing global warming. Now, if we would use that space that we have calculated exclusively to remove CO2 from the atmosphere, this would add up as a central estimate to roughly 0.7 degrees of warming that can be reversed. This estimate is an absolute ceiling for what this storage space can deliver, because it assumes that every ton stored is indeed removed from the atmosphere and is not used to, for example, capture carbon dioxide from fossil fuels that are still being burned, but instead of being released into the atmosphere are then stored again on the ground. And it also assumes that while we are removing carbon dioxide from the atmosphere, there are no other activities ongoing that still continue to emit carbon dioxide in atmosphere. So the 0.7 degrees, the central estimate is an absolute ceiling.

Chris - And it's not very much, is it? It's quite a low ceiling. When you think that we think with what we've already done, we've well and truly breached that. So we couldn't even reverse what we've already done if we use all of what you think is there at our fingertips and sequester that carbon back into the ground.

Joeri - Currently, we are roughly at 1.4 degrees of global warming. We would currently not have kind of the safe storage space to fully reverse this. We would have roughly the space to maximum reverse half of this. I do want to highlight here that our estimate really provides today's estimate. And I would believe that if we really start trying, we will find ways to improve this. But that doesn't mean that today we need to kind of trust that we will be able to remove more. So that's why we call this a prudent limit. We say this is the amount that you should count with today until proven otherwise.