Illustration by Ellery Studio

Negative emissions: ESYS experts on an essential building block for climate protection

22. June 2022

Trees protect the climate because they bind carbon. However, it is also technologically possible to remove carbon from the atmosphere and store it. In its coalition agreement, the German government acknowledges the necessity of such "negative emissions" – even though they have been discussed controversially in society. Calculations show: Greenhouse gas neutrality will only be achievable if ambitious measures of avoiding CO2 are supplemented by negative emissions. The academy project "Energy Systems of the Future" (ESYS) answers the questions of which extraction methods are available, what opportunities and risks they entail, and what role natural carbon sinks such as forests play "in a Nutshell!".

Renewable energies instead of coal-fired power, heat pumps instead of oil-fired heating, electric cars instead of combustion engines: measures to avoid greenhouse gases are well known. But calculations by the Intergovernmental Panel on Climate Change (IPCC) show that they alone are no longer sufficient to achieve climate neutrality. While a climate-neutral energy supply is possible, some residual emissions from industry and agriculture can hardly be avoided. The possible solution: CO2 that has already been emitted must be removed from the atmosphere to create so-called negative emissions. From the second half of this century on, according to the IPCC, even more carbon dioxide will have to be pulled out of the atmosphere than is still being emitted. Experts from the ESYS academy project therefore see negative emissions as an essential building block for climate protection.

In its latest edition In a Nutshell! "What are negative emissions and why do we need them?", the project initiated by the science academies acatech, Leopoldina and the Union of German Academies outlines the current state of research, explains methods of carbon dioxide removal and names their respective advantages and disadvantages. According to the experts, the costs, consequences and risks of the different processes must be carefully weighed up against each other in order to set the course for the future in the best possible way. There is not much time left: In order to achieve global climate neutrality between 2070 and 2100 and to limit global warming to 1.5 degrees, carbon capture must start well before 2050.

Natural carbon sinks and technological methods: risks and potentials

Forests, grasslands and wetlands can store carbon and thus reduce the CO2 content in the atmosphere. Protecting these ecosystems and afforestation will be a task of climate protection. However, relying solely on natural carbon sinks to store CO2 is risky, experts say, because the potential is limited. Moreover, it is often uncertain how long the carbon will remain stored in vegetation and soil. Pests, droughts and fires can damage forests so badly that the stored CO2 escapes back into the atmosphere. This is a risk that is increasing as climate change progresses. The high demand for land can also exacerbate conflicts of use if the land is needed for the cultivation of food crops, for example.

Technological methods such as direct air carbon capture and storage require less space but more energy and financial input. Carbon capture and storage is used to inject CO2 underground and store it. The risk of the stored CO2 being released back in the atmosphere is lower than with natural carbon sinks. Nevertheless, CCS has been discussed controversially in society.

No free pass for more CO2, but a necessary complement to greenhouse gas reduction

One thing is clear: climate neutrality can no longer be achieved without negative emissions. The slower the global community reduces its greenhouse gas emissions, the more negative emissions it will need to achieve its climate targets. However, relying on too much potential is not wise, because it is still unclear how much CO2 can be permanently removed from the atmosphere - and with what side effects. That's why, in the view of the experts at ESYS, negative emissions are a necessary complement to, but not a substitute for, ambitious conservation measures. The task now is to weigh up the significance of negative emissions in the climate protection strategy, as well as the costs, risks and potential of the different processes, and to discuss them on the political level and in society.


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