Carbon Dioxide Capture: Part II

Carrying on from the last post, Carbon Dioxide Capture is a technique to prevent carbon dioxide from reaching the atmosphere in the first place as well as being a method to remove some of the existing carbon dioxide currently in the atmosphere. The previous post focused on the methods of this form of Geo-Engineering and this post will now look at the benefits, drawbacks and feasibility of this method. Carbon Dioxide Removal techniques are often thought of as longer term schemes compared to some of the solar geo-engineering methods suggested because removal of carbon dioxide is slow and therefore the response of climate is also slow. This needs to be considered when attempting to assess the feasibility of all geo-engineering schemes.

Figure 1: Carbon dioxide capture plant in Malaysia

One key positive of carbon dioxide capture is that the technology to achieve this is already available and in use presently. The processes involved in the capture of carbon dioxide in power plants can be easily applied to atmospheric carbon dioxide by capturing air and processing it. This means that the technology of this form of geo-engineering is far more advanced and more rigorously tested that those of other geo-engineering schemes that are still in the research phase. The option to implement this method is therefore possible in the short term as an attempt to begin to reduce carbon dioxide levels.

Evidence from Iceland has found that underground storage of carbon dioxide is much more promising than first thought. CO₂ pumped underground to volcanic basalt rock converted to a solid far more quickly than previously expected, just two years rather than hundreds to thousands of years. Even more positive is the fact that this rock type is widely distributed worldwide suggesting that this a viable method for storing the carbon dioxide captured from power plants and from the atmosphere. The conversion to solid is more beneficial than storing CO₂ underground as a gas due to the risk of leakages. This further advocates the implementation of carbon dioxide capture and storage as soon as possible.

Despite this, capture of existing atmospheric carbon dioxide would have limited effects on atmospheric CO₂ in the short term because of the ocean-atmosphere flux. This flux is the process by which carbon dioxide is exchanged between the ocean and atmosphere constantly. Around a quarter of carbon dioxide emitted by humans in the last two decades was taken up by the ocean. The oceans are therefore a key carbon ‘sink’ (store). By reducing the amount of carbon dioxide in the atmosphere, the ocean-atmosphere flux would increase the transfer of carbon dioxide from the oceans to the atmosphere – a process known as outgassing. This replacement of the carbon dioxide that had been taken out of the atmosphere therefore would not have significant impacts on climate change for a long period of time. This is not to say that in the short term it is not positive because the removal of carbon dioxide from the oceans would reverse the existing trend of ocean acidification that is threatening corals and other ocean species. Overall, atmospheric carbon dioxide capture would have an influence on climate change in the long term and help reduce ocean acidification in the short term which are both very positive.

Atmospheric carbon dioxide capture is unfortunately far less effective than capture in power plants. Therefore capture of past emissions would have much less impact on climate change. Atmospheric capture is less effective because the concentration of carbon dioxide in the atmosphere is only 0.04% compared to around 10% in power stations. This also makes it far less economically justifiable as CO₂ is costly to capture. There is great variation in the cost of carbon dioxide capture because there are a wide variety of factors at play such as plant size, efficiency, fuel cost, etc.. Despite this, I feel that with the current state of climate change and the expected increases in temperature and other changes associated in the future, the benefits of implementing such schemes both in power plants and for atmospheric capture outweigh the financial costs and the other more minimal environmental costs such as leakages from underground stores.

On the whole it is difficult to estimate the financial costs associated with carbon dioxide capture and storage at power plants and from the atmosphere because of the variety of different factors that play a role, most notably the method of carbon capture. One paper estimated that air capture devices could each capture around 400 tonnes of CO₂ per year. Despite being a relatively small amount, it could still have an impact.

To conclude, I believe there are significant advantages to the use of carbon capture in both power stations and atmospheric capture to reduce the amount of carbon dioxide added to the atmosphere in the future and existing carbon dioxide contributing to climate change. It would also be straightforward to suggest that the benefits of this form of geo-engineering heavily outweigh the negatives. Carbon capture, may be expensive to implement but I challenge anyone to think of a form of geo-engineering that is sufficiently effective that is inexpensive. In order to reverse the impacts of anthropogenic emissions, a large (and expensive) solution is needed. This is simply unavoidable.