The world warmed by 1.5 degrees Celsius last year, more than before industrialization, and wildfires, droughts, floods, and other extreme weather events are expected to become more frequent, intense, and deadly. To limit global warming to 1.5 degrees Celsius and prevent such a scenario, the nearly 200 countries that signed the Paris Agreement on climate change will need to not only significantly reduce greenhouse gas emissions, but also take steps to remove carbon dioxide (CO 2 ) from the atmosphere and permanently store it on or below the Earth’s surface.
Previous analyses of the potential, costs, benefits, and limitations of various carbon dioxide removal (CDR) solutions for climate change mitigation have focused primarily on three strategies: bioenergy with carbon dioxide capture and sequestration (BECCS), which involves converting carbon dioxide-absorbing industrial waste into fuel , or directly burning the carbon dioxide to produce energy in the plant, thereby producing a safe fuel; afforestation/reforestation, whichinvolves planting large numbers of CO2-absorbing trees; and direct air carbon capture and storage (DACCS), which captures and sequesters CO2directly from the ambient air and injects it into geological reservoirs or embeds it in durable products.
A new study by researchers at MIT’s Center for Sustainability Science and Strategy (CS3) first expands the options to include biochar (carbon extracted from plant matter and stored in the soil) and enhanced weathering (EW) (spreading very finely ground rock particles over the soil to sequester carbon dioxide) to provide a more comprehensive and effective analysis of CDR. The study then evaluates all five options individually and in combination to assess their potential to meet the 1.5C target, as well as their impacts on land, energy, and policy costs.
The study, published in the journal Environmental Research Letters , draws three key conclusions, supported by a multi-regional, multi-sectoral economic prediction and policy analysis (EPPA) model.
First, the most cost-effective and least-impactful step policymakers can take to achieve global net emissions reductions is to diversify their CDR portfolio, rather than relying on a single option, which is an important step toward meeting the 1.5C target. This approach not only reduces total cropland and energy use, but also increases food security and reduces negative impacts such as reduced energy availability.
By diversifying across CDR options, the most cost-effective net emissions strategy is demonstrated, with a peak CDR use of approximately 31.5 gigatonnes of CO2 per year by 2100. The study identified BECCS and biochar as the most cost-effective for removing CO2 from the atmosphere , followed by EW, while DACCS was not competitive due to its high capital and energy requirements. Despite logistical and other challenges, biochar and WB could improve soil quality and productivity on 45 percent of all cropland by 2100.
“Diversifying the CDR portfolio is the most cost-effective strategy to achieve net zero emissions, as it avoids dependence on a single CDR option, thereby reducing and redistributing negative impacts on agriculture, forestry and other land uses, as well as the energy sector,” said lead author Solene Cicciardi during a post-study briefing.
Second conclusion: There is no optimal CDR package that works well at the global or country level. The optimal CDR package for a given region depends on the local technological, economic, and geophysical conditions. For example, in places like Brazil, Latin America, and Africa, afforestation and reforestation have enormous benefits, sequestering carbon in more protected forest areas, and helping to protect the planet’s well-being and human health.
“When designing sustainable and cost-effective CDR packages, it is important to consider the availability of regional agricultural, energy, and carbon storage resources,” said Sergey Paltsev, associate director of CS3, senior researcher at MIT’s Energy Initiative, and lead author of the study. “Our research highlights the need to improve our understanding of local conditions that make some CDR options preferable to others.”
Finally, MIT CS3 researchers show that delaying the deployment of a large set of CDRs would be very costly, leading to a significant increase in carbon prices worldwide, which would hinder climate mitigation efforts needed to meet the 1.5-degree target.
