While growing climate change may require carbon removal, the technology isn’t likely to be easy, cheap, or an adequate solution to climate problem, John Shepherd argues in an opinion piece for Newsweek.

While carbon removal techniques are diverse — ranging from increased tree and algae cover to absorb carbon from the atmosphere, to engineered chemical absorbents that “scrub” CO2 directly from the air to be buried deep underground — these technologies are both difficult and expensive. While both the U.K. Royal Society and the U.S. National Research Council have found that large-scale carbon removal would be difficult, a joint communique from U.K. learned societies have concluded that carbon removal may be required if we are to limit climate change to two degrees of warming.

A new study in Nature Communications finds that even under the IPCC’s most optimistic emissions scenario (RCP2.6), a limit of two degrees warming would require us to remove anywhere from a few billion to ten billion tons of carbon every year from the atmosphere. To put this in perspective, Shepherd points out that we currently emit about eight billion tons of carbon dioxide every year globally, so the scale of this proposed carbon removal is immense: equal to the present global scale of mining and burning of fossil fuels.