Negative emission technologies include different technologies that can remove carbon dioxide directly from the atmosphere in order to reduce global warming. Some examples of negative emission technologies include tree planting, bioenergy with carbon capture and storage (BECCS), and direct air capture (DAC). But there are also other techniques such as ocean fertilization to increase carbon uptake by phytoplankton, and enhanced weathering, which involve accelerating the natural processes by which rocks absorb carbon dioxide.
Negative emission technologies
Tree Planting
One of the more popular approaches to negative emissions, tree planting can involve both afforestation, where trees are planted in places where there were none before, and reforestation, which involves restoring previously deforested or degraded areas. Trees take up and store carbon dioxide while they grow through photosynthesis.
Bio-energy with carbon capture and storage (BECCS)
BECCS is a proposed technology to extract bioenergy from biomass and capture and store the carbon that is released in the process. As with tree planting, carbon dioxide is removed from the atmosphere through photosynthesis. The resulting biomass is then used for energy production, for example by burning it in a biomass plant to generate electricity. The resulting carbon emissions are captured and then then stored underground.
Direct air capture (DAC)
Here, the carbon dioxide is captured directly from the air in purpose-built facilities. Ambient air is pulled through a filter coated with a chemical that absorbs the carbon dioxide. The result is a purified carbon dioxide gas that can in principle be buried underground. In practice, in the few DAC projects that currently exist, the CO2 is used to help extract more oil (a process called enhanced oil recovery) or for use in a range of products.
Uncertainties with negative carbon emission technologies
In his research, Wim Carton highlights that all of these technologies are associated with uncertainties and problems related to justice, power, and ecosystems and biodiversity. There are also questions related to the economic viability and feasibility of implementing these large scale projects.
– Firstly, will these approaches be implemented in a just way? For example, tree planting projects have often been associated with negative consequences on local communities, raising questions about global environmental justice. While tree planting projects often come with a range of promised co-benefits, the results for project participants are often disappointing. They also cannot guarantee the long-term permanence that is required for negative emissions to work as promised.
Another concern is the enormous amount of land that would be needed to implement land-based carbon removal technologies such as BECCS and afforestation – up to a third of all the arable land on the planet according to some estimates. Implementing these technologies at the scales that some models project would necessarily lead to conflicts with biodiversity protection and food security.
Large-scale carbon removal entails significant risks for food security, poverty reduction, and biodiversity protection. We are seeing the same justice concerns that have long existed for tree plantations, just on a much larger, global scale.
Wim Carton highlights that many negative emission technologies still mostly only exist in models or as demonstration plants, and that it is important to consider the political and economic barriers to commercializing some of these technologies.
– Even when they only exist as a future promise, there is a risk that negative emissions will distract from the difficult near-term political work that is needed to help move society away from fossil fuels.
Carbon removal should not be used as a substitute for ambitious decarbonization, but unfortunately that is the role that it has often played in the past.
Finally, Wim Carton says that some negative emission technologies might be necessary to achieve ambitious climate change mitigation targets, but then it is key that research and policy on this topic proceed not just from projections of the future, but also from an acknowledgement of past controversies, successes and failures.
Wim Carton's and LUCSUS' research on negative emission technologies
Negative emissions and the long history of carbon removal published in WIREs Climate Change on wiley.com
Blog post in CarbonBrief: Learning from the contentious history of ‘carbon removal’
Planting trees in Africa is a dubious environmental strategy: study on lu.se
Research projects:
- Tradeoffs between negative emissions and near-term emission reductions
- Negative emissions and the politics of a projected future: Bioenergy with Carbon Capture and Storage (BECCS), political economy, and the responsibilisation of climate research
