The Interpreter: Felix Havermann on carbon dioxide removal (CDR)

Some scientific terms have made it into everyday discourse. Here, LMU researchers tell us what these expressions mean – and not just with a definition, but also a brief account of how they entered the vernacular.

Felix Havermann: "The idea of removing CO₂ from the atmosphere emerges in the mid-1990s. Experts call it carbon dioxide removal – or CDR. The Intergovernmental Panel on Climate Change (IPCC) adopts CDR in 1995, and in 1997 it appears in the Kyoto Protocol. Carbon dioxide, methane, and nitrous oxide are the main greenhouse gases, with the former making by far the biggest contribution to human-made climate change. Soon, experts realize that reducing emissions from industrial and land-use processes will not be enough to combat climate change.

Just suck greenhouse gases out of the air?

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Another approach besides CDR is solar radiation management, which involves intervening in the Earth’s radiation budget. But because its effects are difficult to control, the concept remains controversial. And so CDR has been the go-to approach for the past decade and more. Currently, the chief CDR method is afforestation/reforestation, which relies on the ability of trees to absorb CO₂ through photosynthesis. The benefits are clear: it is quickly available, cost effective, and already makes up 99% of CDR efforts. Another biological method involves sequestering more carbon in the soil on agricultural land.

Chemical methods such as direct air carbon capture and storage (DACCS) have recently joined the party. DACCS facilities suck in ambient air and filter out and sequester the CO₂. Further research is needed on geological sites that can store the CO₂. One option would be old natural gas wells, which are well surveyed in terms of leaks. An alternative would be marine sediments, but we have so far little experience in this area.

There is room for the further expansion of afforestation and reforestation as well as agroforestry systems, where trees and shrubs are planted on agricultural land. There are also new methods such as bioenergy with carbon capture and storage (BECCS). This involves growing bioenergy crops, which absorb CO₂. The CO₂ that is released during energy generation needs to be immediately captured and subsequently stored. Also pyrolytic methods are being used to transform vegetation carbon for the long-term storage of CO₂ in agriculture soil.

As such, there is not just one method, but a whole range of them, which need to be deployed on a broad scale. Currently, we are removing 2.2 gigatons of CO₂ from the atmosphere worldwide every year, but we are producing emissions of 40 gigatons of CO₂. Yet our efforts remain just a drop in the bucket. Perhaps we will manage to increase CDR to 8-10 gigatons by 2050, but to become carbon-neutral, we need to massively change our lifestyle.

Dr. Felix Havermann is Scientific Coordinator of the Research Programme CDRterra at the Department of Geography at LMU. The BMBF climate program CDRterra evaluates the various methods of CO₂ removal uniformly and comprehensively with regard to their ecological, technical, economic, political and social feasibility.