Removing carbon dioxide from the air as a potential way to combat global warming is referred to as “negative emissions technologies” to distinguish them from technologies that reduce emissions from cars, power plants and other industrial facilities.
There are five major approaches to carbon dioxide removal:
Plant more forests:
Trees remove carbon dioxide naturally, incorporating it into their tissues as they grow. Forests store about one billion to two billion tons of carbon annually, offsetting a chunk of the roughly 10 billion tons emitted by human activity. Reforestation and afforestation, properly managed, could remove a lot more and keep it out of the atmosphere. But planting forests is slow and requires a lot of land. Coordination on the UN and individual governments’ level is needed to make this work.
Crush olivine rock:
This technique is called enhanced weathering, and is based on the fact that some types of rock weather by absorbing carbon dioxide from the air or water. One approach is to use mineral olivine, which is plentiful, crushing it into fine sand and spreading it on land, perhaps along coastlines. But mining, crushing and transporting the billions of tons needed would be expensive and energy intensive. And the carbon removal would still be a slow process. Cheaper and more energy-efficient ways of producing olivine sand and creating other materials and uses are needed to make this approach work. Building roads or buildings with such materials needs further research and coordination.
Using bioenergy and capture the carbon dioxide:
In this high-tech approach, the BECCS, vegetation would be used to naturally remove carbon dioxide. The vegetation would then be burned in a power plant and the carbon dioxide in the exhaust gases would be captured and stored. So far there are only a handful of working BECCS projects; others have been canceled. Among the many questions about the technology is whether emissions are really negative if the carbon cost of growing and harvesting the vegetation is taken into account. More research, development and coordination is needed to make this work.
Sprinkle iron and other nutrients in the ocean:
The idea is that the nutrients would stimulate the growth of tiny marine plants called phytoplankton, which would incorporate carbon dioxide as they grew and then sink to the bottom of the ocean when they died, taking the carbon with them. Generally, however, putting large amounts of metal or chemicals into seawater is considered ocean dumping. Natural solutions have to be developed.
Suck carbon dioxide out of the air:
There has been a significant amount of research into “direct air capture.” Much of the technology is similar to what is used in carbon capture projects at power plants: chemicals bind with carbon dioxide molecules and then are heated or otherwise treated to release them for capture. Several companies, including Carbon Engineering and Climeworks, have developed machines to do this. However, since carbon dioxide level in the atmosphere, harmful as it is, is only 0.04 percent, it would require moving huge volumes of air through thousands upon thousands of capture machines, and powering the machines for decades, which makes this approach unviable at this time. Ways to incorporate the capturing technology into construction and using billions of micro-machines in our everyday life and then disposing of the filters with the captured carbon and burying them in landfills needs to be researched.