What are carbon offsets?

Worldwide greenhouse gas emissions must be significantly reduced in order to limit global warming. From 2050 onward, human activities should only release as much greenhouse gas as is removed from the atmosphere by natural carbon sinks or technical means.

But currently, some emissions are difficult or impossible to avoid, so carbon offset providers offer emission reduction credits, which are often called certificates. Purchasing a certificate is supposed to “compensate” for the emission of a ton of CO2. The providers use the income from certificate sales to support climate action projects that reduce greenhouse gas emissions by the corresponding amount or remove as many tons of CO2 from the atmosphere as the number of certificates sold.

Andreas Oschlies is skeptical about the idea of carbon offsets. “In our research group, we don’t use the term offsets at all,” says Oschlies, who heads the Biogeochemical Modelling research unit at the GEOMAR Helmholtz Centre for Ocean Research Kiel. The Paris Climate Agreement also makes no mention of offsets. The only way to compensate for greenhouse gas emissions is to permanently remove an equal amount of greenhouse gases from the atmosphere, whether by carbon capture or by actions such as planting more trees and letting them grow,” says Oschlies.

However, the certificate providers also count measures that avoid emissions but do not actively help to remove CO2from the atmosphere as offsets. Such measures can include building wind farms that replace coal-fired power plants and thus reduce CO2 emissions. Many certificates stipulate that no logging will take place in a certain forest. “The forest owners receive money for that. And in the following year, they might accept a further payment for not logging, if necessary from a different certificate provider. All of the forest’s carbon is credited as avoided emissions each time,” criticizes Oschlies. And even when a tree is planted, he adds, the amount of CO2 it actually absorbs from the air over a certain period needs to be calculated very precisely. 

The precision and reliability with which certificate providers calculate the amount of emissions avoided or of greenhouse gases extracted from the atmosphere by the measures they support is disputed. Research by journalists from Die Zeit and The Guardian revealed in 2022 that over 90 percent of the certificates from the largest provider on the market failed to deliver the promised reduction of greenhouse gases. Oschlies also says, "These certificates are no help at all for the climate.

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