What climate scientists talk about when they talk about carbon removal

Last week, around 2,000 climate experts gathered at the Our Common Future Under Climate Change Conference hosted by a consortium of NGOs in advance of the upcoming UN COP21 climate negotiations. The idea of removing carbon dioxide from the atmosphere to create “negative emissions” was a hot topic of conversation at the Conference. Below, I’ve summarized my key takeaways about what scientists were saying about carbon removal at the Conference:

Discussion on the main stage at the Our Common Future Under Climate Change Conference.

Discussion on the main stage at the Our Common Future Under Climate Change Conference.

Takeaway 1: Carbon removal is increasingly embedded in projections of what we will need to do in order to curtail climate change. The consensus documents from the conference state: “to limit warming to 2°C, emissions must be zero or even negative by the end of the 21st century.” Carbon removal solutions will be necessary to transform the economy to generate negative emissions, as more traditional climate mitigation strategies (such as renewable energy, energy efficiency, avoided deforestation, etc.) can only get us to zero emissions – not below zero. And it’s not just "below zero" emissions that we need carbon removal for, as carbon removal solutions also make up a significant component of many pathways for reducing greenhouse gas emissions by 40-70% by mid-century.

Takeaway 2: But…scientists still have many untested assumptions about deploying large-scale carbon removal projects. Today, carbon removal solutions have not been deployed at large scale. As a result, projections of large-scale carbon removal deployments rely on many untested assumptions (around cost, sustainability, scalability, etc.). For example, many projections that include carbon removal solutions involve the large-scale deployment of bioenergy systems, yet critical uncertainties remain around our estimates of:

  • The sustainable supply of bioenergy crops;
  • The ability for bioenergy crops to co-exist with growing demand for food; and
  • Public acceptance about underground carbon sequestration

The scientists working on carbon removal systems are the first to admit these limitations in their models. But unless these assumptions are stress-tested promptly, we risk setting climate policy in a direction that may end up ultimately infeasible and/or unsustainable.

Takeaway 3: Scientists are focusing on a narrow set of carbon removal solutions today. Most of the talk about carbon removal at the conference focused on bioenergy coupled with carbon capture and storage (BECCS, as it is referred to in the scientific community) and forestry solutions (such as reforesting degraded lands or planting new forests altogether). But innovators are also working on other carbon removal methods: direct air capture systems, agricultural techniques with the potential to sequester carbon in soils, and mining techniques that use minerals to sequester carbon directly from the atmosphere, for example. While these latter techniques might have even more uncertainties surrounding them than do bioenergy/forestry approaches, many scientists still think that it is worthwhile conducting further research on these systems to learn how they might broaden the portfolio of feasible, sustainable, and scalable carbon removal solutions in the future.

Takeaway 4: The scientific conversation on carbon removal is an implicit call for increased R&D for carbon removal solutions.

Carbon removal is the elephant in the room for the climate change conversation: scientists are increasingly convinced we need carbon removal solutions, yet significant uncertainties remain as to what carbon removal solutions can scale in a sustainable, cost-effective way.

Carbon removal is the elephant in the room for the climate change conversation: scientists are increasingly convinced we need carbon removal solutions, yet significant uncertainties remain as to what carbon removal solutions can scale in a sustainable, cost-effective way.

In many regards, carbon removal is the elephant in the room in today’s climate change conversation. While scientists increasingly assume that carbon removal solutions will provide a critical component in the fight against climate change, they are quick to acknowledge that we aren’t researching and building carbon removal projects nearly as fast as needed to ensure we actually can remove carbon from the atmosphere at the scale needed. Implicit in this conversation is the need for more research and development across a full portfolio of carbon removal solutions – something that is critical for policymakers and climate negotiators to make explicit as soon as possible.