What do trees and the next generation of coal power plants have in common? The deceptively simple answer is carbon sequestration.
How Carbon Sequestration Works
When we breathe, we breathe in oxygen and breathe out CO2. When plants breathe, it is the opposite: they take in CO2 and exhale oxygen. They do this by breaking apart the carbon dioxide molecule into its two constituents, oxygen and carbon. The plant uses these atoms to produce energy, then excretes the oxygen while the carbon is stored in the plant. [1]
When the plant stores the carbon, it is sequestering it, thus the term carbon sequestration. Plants have been sequestering carbon for a very long time, so over time the amount of carbon dioxide in the atmosphere has decreased. During the carboniferous, levels of CO2 in the atmosphere were three times greater than they were before industrialization. [2]
Why Do We Need to Sequester Carbon?
Notice that the carboniferous was three times greater than pre-Industrial CO2 levels. The problem is that carbon is made from old plant matter, and coal is the primary power source of our planet, providing 54% of the world’s power. [3]
When you burn coal, all the carbon that was previously contained in it is released back into the atmosphere. The enormous amount of coal burning means that an enormous amount of CO2 has been released back into the atmosphere over a period of the last century, and indeed CO2 levels are higher now than they have been in 8,000 years, the longest back that we can reliably sample directly. [4] The problem is that CO2 is a greenhouse gas, meaning that CO2 stores the sun’s energy more easily than oxygen. This is believed to have lead to the planet warming up. Few things do well with rapid change, and species that have adapted to the colder temperatures and lower amounts of CO2 caused by sequestration have not responded well to the change. It’s possible that we may see a mass extinction at least partially caused by greenhouse gasses. [5]
One way believed to help cease global warming is to sequester the CO2 released from our coal power plants.
How is Carbon Sequestered?
While the technology to capture the CO2 is still fairly far from market, several technologies already exist for sequestering it. Below are some of the most promising.
Subterranean Injection
Many underground structures can store CO2. One of the best would be an unminable coal seam. These are ideal because the surface of the coal chemically reacts with the CO2, and the gas sticks to it. [6]
This method is great because, unlike some other subterranean injection techniques, there is little chance of leakage. CO2 leaks can be extremely dangerous to anything that gets in their way (i.e. plant life or people). In 1986, 1,700 people were killed at Lake Nyos near Cameroon, West Africa when a natural bubble of sequestered CO2 gas broke the surface. [6]
Ocean Storage
Another approach is to pipe the CO2 deep underwater and let it bubble upwards, where the water will capture most of it. This is a highly effective approach, but it can also cause mass die-offs as the CO2 poisons the ocean life. For some reason, that is not an appealing side effect.
Mineral Storage
Yet another approach is to mix the CO2 with chemicals to form hydrocarbons, which we can then easily store. Essentially we would chemically be making coal that doesn’t produce that much energy. This is a simple, promising option, but getting the chemicals needed takes energy, decreasing the return on investment of burning coal.
We will have to wait a few years to see which sequestration technique is favored. All of them have drawbacks, so it may come down more to politics than science. Either way, carbon sequestration is coming.
Sources:
1. http://biology.clc.uc.edu/courses/bio104/photosyn.htm
2. http://www.ucmp.berkeley.edu/carboniferous/carboniferous.html
3. http://www.ucsusa.org/clean_energy/coalvswind/c01.html
4. http://news.bbc.co.uk/2/hi/science/nature/5314592.stm
5. http://en.wikipedia.org/wiki/extinction_risk_from_global_warming
6. http://en.wikipedia.org/wiki/carbon_capture_and_storage
