Visual representation of CO2 emissions in North America and the dispersion of these emissions into … [+] the atmosphere. Source: NASA

Carl Robichaud, Deep Sky

2024 is the first year to exceed 1.5 degrees of warming, widely accepted as the one-way door where irreversible climate breakdown starts to occur. In the global fight against climate change, achieving “net-zero” carbon emissions is not just a target; it’s a necessity to limit the Earth’s temperature rise further. Recent research from UC Berkeley and ETH Zurich has revealed that the concept of “durability” in carbon dioxide removal — how long captured carbon stays out of the atmosphere — is a critical factor that could make or break climate goals.

The Durability Dilemma

To address climate change effectively, the Intergovernmental Panel on Climate Change (IPCC) and the Paris Agreement have emphasized the need for carbon dioxide removal methods to durably and permanently store CO₂. But what does “durable” mean in practice? Definitions vary widely, from storage durations of just a few decades to as large as millennia. This disparity in duration significantly impacts the effectiveness of carbon removal efforts and, in turn, global climate targets.

Using a climate model, the research team investigated various CO₂ storage durations and their implications for temperature outcomes. They discovered that net-zero emissions strategies relying on short-lived storage options — those lasting a century or less — will fall short of achieving the desired temperature stabilization. For instance, with 100-year storage duration, the study predicts an additional warming of 1.1°C, even if net-zero emissions are technically achieved. This gap could prove detrimental to reaching Paris Agreement targets, which aim to limit warming to below 2°C and ideally 1.5°C above preindustrial levels.

Permanent vs. Temporary Storage: Why 1,000 Years is the Benchmark

For net-zero emissions to effectively neutralize the effects of residual CO₂ emissions, captured carbon must be stored for at least 1,000 years. Anything shorter will jeopardize the climate goals set by the Paris Agreement. This longevity requirement emerges because fossil fuel based CO₂ emissions remains in the atmosphere for millennia, continuously contributing to global warming. To truly offset these emissions, carbon removal solutions must provide a comparably lasting “cooling effect.” Only permanent storage, such as geological sequestration, has the potential to achieve this balance.

Moreover, the scientists advocate for a “like-for-like” approach to neutralization, meaning that fossil-based CO₂ should ideally be balanced by geological or similarly technology-based durable solutions like direct air capture, rather than by short-term, nature-based options like afforestation, which have uncertain durability due to risks like wildfires or deforestation.

While nature-based solutions like reforestation and soil carbon sequestration are crucial for reducing atmospheric CO₂, they have limited longevity and are vulnerable to natural disturbances. For instance, forests can re-release stored CO₂ through wildfires, and carbon in the soil can be depleted by agricultural practices.

Unfortunately, many current carbon removal approaches, particularly those using biological methods, do not meet the threshold for permanent storage and may need to be re-evaluated especially as the vast majority of carbon credits sold today are nature-based solutions. Relying on these temporary storage methods results in the re-release of CO₂ into the atmosphere, nullifying the climate benefit over time.

A Call for Clearer Durability Standards

The lack of a clear durability standard for carbon removals undermines the credibility of current net-zero claims by corporations and governments. The fast-growing carbon offset market, estimated to eventually be worth billions, often counts temporary carbon removals as equivalent to permanent solutions, creating a loophole that could allow companies to delay significant emissions reductions. Setting a durability benchmark of 1,000 years provides a tangible metric for assessing which carbon removal methods align with long-term climate goals.

This durability standard also has implications for policymakers. To incentivize the development and deployment of durable carbon removal technologies, new policies are needed that reflect the true costs and climate benefits of long-term storage. This may include stricter regulations on carbon offset markets, with limits on the use of temporary removals to offset fossil-based emissions.

Geological storage methods, such as injecting CO₂ into underground rock formations, currently offer the most viable path to achieve lasting carbon sequestration. Meanwhile, research and investment in other promising methods, like direct air capture with mineralization, could pave the way for alternative solutions that satisfy the durability criteria.

Today, technology-based carbon removals like direct air capture are also the most expensive, selling at approximately $700 to $1000 per tonne of CO2 captured. Part of the justification for this high cost is the permanence, durability, and traceability of direct air capture as every molecule of CO2 captured from the air and stored underground can be directly measured. Understandably, this measurement is more difficult for nature-based solutions. As the technology improves and the deployment increases, costs for direct air capture are expected to decrease substantially – following a similar cost trajectory to solar, wind, or electric vehicle batteries. Disclaimer: I work for Deep Sky, a carbon removals project developer based in Canada building direct air capture plants.

For net-zero strategies to be effective, they must be backed by carbon removal methods with durability that matches the persistence of anthropogenic CO₂. Anything less risks a false sense of progress and potentially undermines decades of climate action. Temporary carbon removal methods still have a role to play. While they may not be suitable for offsetting fossil CO₂ emissions, these methods can contribute to lowering peak temperatures in the near term, which can buy time as durable solutions are scaled up. Additionally, temporary carbon removal methods often provide co-benefits, such as enhancing biodiversity, improving air and water quality, and supporting local communities.

As the world moves toward net-zero emissions, defining and implementing a durability standard for carbon removal could be one of the most critical steps in realizing a sustainable, climate-safe future.