Guest post: Learning from the contentious history of ‘carbon removal’

Large-scale carbon dioxide removal (CDR), also referred to as “ negative emissions ”, is increasingly seen as a key component of climate change mitigation pathways that limit warming to 1.5C or 2C. 

Its prominence in global pathways derived from technologically focused integrated assessment models has spurred a growing scientific literature that explores the potential opportunities , risks and trade-offs of relying on CDR.

This literature – even when it questions the assumptions and feasibility constraints underpinning large-scale CDR – tends to frame the various CDR approaches as novel and untested, and mostly focuses on hypothetical future scenarios. Yet CDR has a longer and, in many ways, more tangible history than this framing suggests – the lessons of which are largely overlooked in much of the current debate. 

In our new paper, published in WIREs Climate Change , we review this history and draw out some key lessons for scaling up implementation of CDR. 

The carbon removal debate

While technological and industrial CDR methods – such as direct air capture and enhanced weathering – are relatively new entrants to the mainstream climate conversation, land-based CDR has been on the climate agenda for decades. In anything but name, it has been part of the mainstream climate discussion at least since the 1990s . 

Negotiators at international climate talks debated the inclusion and definition of carbon sinks and carbon sequestration in the Kyoto Protocol for years, before finally settling on rules that allowed net carbon accounting from anthropogenic land use, land-use change and forestry – excluding avoided deforestation.

Land-based CDR has since made its way into various policy mechanisms, mostly in the form of forestry projects in the global south. It has played a minor part in the Clean Development Mechanism – the compliance offsetting market established under the Kyoto Protocol – and has featured more significantly on the voluntary carbon market , where individuals and companies can choose to offset their emissions by investing in sustainable development projects.

CDR is also included in REDD+ , the UN’s flagship policy to reduce both deforestation and forest degradation. REDD+ mechanisms have been a contested discussion point in international climate negotiations since 2005.

Aerial view of deforestation of rain forests in Brazil near Amazon River. Credit: Chad Ehlers / Alamy Stock Photo. While none of these projects has occurred at anything near the scale now imagined in modelling studies , these historical experiences are of direct relevance to the current conversation on negative emissions. 

They contain important lessons about, for example, the obstacles and opportunities for implementing and governing CDR ; the risks and challenges with integrating CDR in carbon markets ; the concerns of, and impacts...