Capturing Carbon to Counter Climate Change
Chris - Herbert, welcome to our punt. Welcome aboard!
Herbert - Thank you. It's a little rock-y but it's fun sitting here.
Chris - Tell us - this carbon business, we'd like to think that weather like this isn't just the result of global warming. What can we do to try and offset the carbon that we might be pumping out into the atmosphere?
Herbert - You know we're pumping out 27 billion tonnes of carbon dioxide every year into the atmosphere. It's been rising steadily since the beginning of the industrial revolution. At the same time the global average temperature has been rising. We're very concerned that it may be mankind putting this carbon dioxide into the atmosphere that not only is warming the atmosphere but is leading to terrible natural situations like Katrina and the droughts of Australia and the great heat wave of 2003 that killed so many people in Europe. We'd like to see how we can either put less carbon dioxide into the atmosphere because we use less energy by burning less fossil fuels or by storing it in large reservoirs, porous reservoirs beneath the surface of the earth.
Chris - Some people say that the reason that you see a rise in CO2 with a rise in temperature as the water doesn't absorb as much CO2 when it's warmer. So if you warm the world up CO2 comes out and goes in the air.
Herbert - What is clear is that there is a good chance that because of the increase carbon dioxide that we're putting into the atmosphere the temperature is rising because of that.
Chris - What sort of strategies are there to try and get the carbon dioxide out of the atmosphere and also to prevent us putting it into the atmosphere in the first place?
Herbert - We could just be much more efficient in our energy use. We don't need really to warm our houses as much as we do. We don't need to drive individually around the country. We could have to or three at a time coming into work. There's no doubt that we could reduce the amount of energy that we use and be just as comfortable and just as happy. As to actually what we would do with the carbon dioxide there are lots of suggestions. The one that is most likely to work is to store carbon dioxide for at least ten thousand years in these porous reservoirs that are at the moment full of salty water. But there are other suggestions for reservoirs such as coal seams, brown coal seams that are not attractive as far as mining them is concerned from a financial point of view. They are also very porous and we could put it in there or depleted oil reservoirs. [There is] not as much storage space there available to us. That's another possibility.
Chris - What are the mechanics of getting the CO2 there in the first place?
Herbert - The point is that normal carbon dioxide as we know it is a gas. A gas takes up a relatively large amount of space compared to a liquid, sometimes up to a thousand times more. We can compress the gas into a liquid by taking it down to a minimum of 800m but better somewhere between 1km and 2km. You have to pump it down 1km normally where it becomes supercritical gas, it's called. It's like a liquid, it has a density close to water but ¾ that of water. Then it flows out into these pores in the rock really just like oil has been formed in pores.
Chris - How do you keep it there?
Herbert - The idea is that there will either be some totally impermeable seal, just as oil is sealed in reservoirs that's been made hundreds of thousands of years ago. The other possibility which has been looked at but only from a theoretical point of view is to somehow play some game with the density. The density of the liquid like carbon dioxide than that of the surrounding liquid and hence gets trapped. That's a very dangerous business it seems to me because something could always go wrong and it somehow gets rather less dense and it comes to the surface.
Chris - Researchers in America who are looking at the possibility of putting the CO2 into water in the ground where it forms a dilute acid and then reacts with carbonates in the rock and you end up with the CO2 becoming almost like limestone. It's sequestered as a rock.
Herbert - The question is how much energy is needed to do that, in the sense energy to make the chemical transfers. My understanding is the energy is really quite considerable and also the process is very, very slow. The thing we have to realise is we are putting in an enormous amount of carbon dioxide, 27 billion tonnes a year. The biggest field projects at the moment have been sequestering something like a million tonnes every year. We need something like a 100,000 such field stations. We're a long way from getting there.
Chris - Also, where we're producing the CO2 isn't necessarily where we'd want to sequester it so there's the other problem, I presume, of getting it to where we want to store it.
Herbert - We're not going to transport it far. My belief is that we'll try to do something with it where it's formed. That's an important point because there's virtually no work done at all anywhere over the former Soviet Union, over South America, almost all of the southern part of Africa yet they produce a considerable amount of carbon dioxide. At the moment no thought's been given to where you might sequester their carbon dioxide.
Chris - You mentioned parts of the Soviet Union. A lot of that stuff is in what was permafrost which is now melting. Organic matter is getting into water and very quickly getting digested and turning into methane and CO2. I suppose there's that to take into account as well?
Herbert - Yeah. That is a recent interest and people don't know exactly how much methane there will be and what the potential problems will be there. That is something I think we need to look at very carefully as the Earth warms up and as you say much more methane can come out into the atmosphere. This would not be direct anthropogenic input of methane but it is a consequence of anthropogenic effects.
Chris - Are you worried?
Herbert - No, I'm never worried. Yes, the temperature may go up a little bit and yes, we may have a number of natural catastrophes but I'm sure we'll see our way around.