Removing CO2 from the Air

30 OCT 2019
There is much talk on reducing our emissions of carbon dioxide into the atmosphere - but we're already a long way from where we need our air to be. Somehow, somewhen, we need to be removing the carbon dioxide from the air and sequestering it. Not just putting it into trees, but back into the ground from where we rashly pulled it.

There has been a lot of money in getting the carbon out - but it will be an expensive proposition to put it back in. Or are we content to live with the consequences of the mess we have made?

Big Think is a great site for expanding your knowledge and giving you new perspectives on current events and developments in science and technology. I highly recommend a subscription. Recently it gave the low down on the current state of the art on Greenhouse Gas Removal. It's a thought provoking read.

It touches on the most realistic and obvious - Reforestation. This is one that we all like because it has obvious benefits and we all like to see trees rather than desert or concrete. The notion that we live on a green planet largely comes from our love of trees. The fact that we should all be bluies and not greenies is probably only obvious once we look back on our pale blue dot from space. But it would never be enough. We need that land for agriculture, and there is just not enough forest to pull out the carbon dioxide we've released. We should do it anyway for water conservation, and the preservation of environments for forest species. And while carbon dioxide is stored in trees it will eventually be released into the air. We're banking time - not solving the problem.

Wetland Restoration is a similar strategy, and we have destroyed so many wetland ecosystems that it is past time to restore them. So again it is something we should be doing anyway. Wetlands, especially mangroves, are excellent ways to protect coastlines from the erosive effects of rising sea levels. Wetlands are nurseries for the fish we eat, and homes too for birds, and endangered mammals. They are fantastic ecosystems that we can not do without. They should be protected, nurtured, and restored wherever possible. And we will reap benefits over and above the carbon dioxide they will store.

Soil Carbon Storing is called sequestration by the article, but it is a fragile storage. Unless it is well locked up, and protected, then eventually the carbon will return to the atmosphere. However we should do this anyway. Carbon improves soil quality, and moisture retention. Organic matter buried in soils also contains other minerals useful for plant growth. When I compost and dig the results into my garden I'm doing double duty. As an alternative to composting, I dry vegetation, then shred it into a fine mulch, and then dress the soil to keep weeds down, and retain moisture, Eventually this mulch is turned down into the soil where it is stored.

Related to Soil Carbon Storage is Biochar. This is when, ironically, vegetation is heated in the absence of oxygen, to create a charred material that is resistant to rot. This is then ground up and can be dug into the soil. When in the soil it has multiple benefits, regulating pH, and changing the biochemistry of soil bacteria. Terra preta is an artificially enhanced soil found throughout the Amazon basin. It is incredibly fertile and was used by indigenous farmers to maintain fertile soils for agriculture for thousands of years. And incidentally locking up a lot of carbon. A modern-day process could do much the same for soils worldwide.

Enhance Weathering is an acceleration of a process that naturally sequesters carbon in carbonate rocks. Concrete weathers and absorbs carbon in a similar manner - so once poured it will begin to absorb carbon dioxide. Some additives can enhance this process. However it is not clear how weathering could be scaled up greatly and more research is required. But it is an interesting topic, and one I'll look out for more updates.

Bio-energy Carbon Capture and Storage is a fancy name for burning vegetation and then capturing the flue gases and then storing them. Ideally this is a win-win because burning can make energy at a profit, to fund the storage process. But it will still mean a lot of material will need to be grown. The most useful might be the byproducts of food production. For instance wheat chaff, sugar cane bagasse, or maize stalks and cobs. However Carbon Capture and Storage has not been shown to work for smokey flue gases - only for some natural gas flue gases. Processes will need to be improved in order to make this a viable option.

The best option currently is still to reduce carbon emissions now, and to plant trees for the future. More effort on finding solutions to sequestration needs to be made because we already have too much carbon dioxide in the air. There are options over and above the ones discussed in this Big Think article. I'll gather resources for a future blog post.
By Hab3