It is important to note from the outset that reducing emissions is, without question, critical. But it is equally vital to understand that it won’t be enough on its own. The simple truth is that every credible scenario for staying within the 1.5ºC threshold outlined in the Paris Agreement also depends on large-scale greenhouse gas removal (GGR).
Despite the skepticism surrounding GGR, we must be clear: emissions reduction and GGR are not mutually exclusive. Both are necessary to reach our climate goals. Emissions reduction efforts alone are insufficient, and the slow progress we’ve made thus far only reinforces the need for GGR to play a major role in future strategies.
The Underlying Problem
It’s crucial to acknowledge that we have not yet made the necessary strides in reducing emissions. There’s no evidence that a lack of progress is due to the prospect of GGR. However, it is undeniable that the situation is dire. In fact, most scenarios forecasted by the IPCC’s AR6 report make it clear that without a concerted push towards GGR, we won’t achieve the required reductions to keep global temperature increases under 1.5ºC.
That said, GGR should not be seen as an excuse to delay emissions reduction efforts. These two actions must run parallel to each other. One without the other is insufficient to combat the vast amounts of carbon dioxide we have released into the atmosphere over the past centuries. The key challenge is to identify and implement GGR methods that can scale up rapidly while remaining cost-effective and environmentally sustainable.
Evaluating GGR Approaches
When evaluating GGR methods, it’s helpful to consider them within two broad categories: land-based and ocean-based approaches. Each of these categories can be further divided into nature-based and technological solutions. Moreover, within each approach, there are different levels of certainty regarding the effectiveness and permanence of the sequestration.
Ocean-based approaches offer significant opportunities because the ocean is already a vast reservoir of carbon dioxide. In fact, it has absorbed around a third of the CO₂ emissions produced by human activity. However, despite this vast capacity, ocean-based GGR methods still face challenges in terms of environmental impacts and our ability to monitor and verify their effectiveness. For instance, approaches like ocean iron fertilisation, which aims to stimulate phytoplankton growth, come with uncertainties regarding their long-term impact on marine ecosystems and the permanence of the captured carbon.
Similarly, land-based methods—such as reforestation or increasing the carbon content in soils—are valuable but come with risks of reversal. For example, a forest fire could quickly release stored carbon back into the atmosphere, negating any previous sequestration gains. More technological land-based solutions, such as direct air capture (DAC), offer more certainty in terms of measuring how much carbon is being captured and stored. However, DAC comes with significant energy demands, making it an expensive solution to implement at scale.
Scaling Challenges
One of the biggest challenges we face is the sheer scale of the problem. To put things into perspective, the world currently emits around 40 gigatonnes of CO₂ annually. To meaningfully impact climate change, any GGR solution would need to operate at gigatonne scale. This is where many GGR technologies face hurdles. While small-scale laboratory experiments can be promising, scaling these solutions up to the necessary levels presents logistical, financial, and environmental challenges.
For example, direct air capture is a promising technology in which CO₂ is chemically removed from the air and stored underground. However, scaling this up to a level that could capture billions of tons of CO₂ annually would require vast amounts of energy and infrastructure. Despite this, the storage capacity required for such technologies exists—whether in depleted oil and gas reservoirs or deep aquifers. The real challenge lies in making the technology affordable and energy-efficient at scale.
Ocean-based solutions, too, are not without challenges. As ocean temperatures rise, the oceans are already under significant stress. Approaches like growing large amounts of kelp or fertilising the ocean with nutrients could have unintended consequences for marine biodiversity. Additionally, monitoring, reporting, and verification (MRV) remains a significant challenge for ocean-based methods. It’s essential to ensure that these actions lead to additional carbon sequestration and do not simply displace other natural processes that would have occurred in the absence of intervention.
Regulatory and Market Challenges
Another important aspect of GGR is how it integrates with existing climate policies, such as the Nationally Determined Contributions (NDCs) that countries submit under the Paris Agreement. For GGR to be deployed at scale, it must become part of these frameworks. Yet, many questions remain about how to regulate and ensure the credibility of these solutions, particularly when it comes to market-based approaches like carbon credits.
For GGR to succeed in the marketplace, investors need confidence that the solutions they are funding will have long-term impacts. This is particularly challenging when dealing with ocean-based methods, which may involve international waters and require stringent MRV systems to avoid issues like double-counting. Additionally, nature-based solutions like reforestation may be vulnerable to reversals, such as forest fires, which complicates efforts to account for and trade carbon credits associated with these projects.
Building Confidence and Moving Forward
Despite these challenges, there is reason for optimism. The academic community is making strides in understanding the complexities of GGR, and new technologies and approaches are being tested and refined. Over time, as our understanding grows and as MRV systems improve, we can expect higher levels of confidence in the efficacy of GGR solutions.
That said, time is of the essence. As global temperatures continue to rise, the need for effective GGR solutions becomes more urgent. The challenge now is not only to develop these technologies but to scale them up rapidly and integrate them into global climate policies in a way that ensures they are both effective and equitable.
Finally, while the road ahead is filled with challenges, the potential of GGR to help mitigate the worst impacts of climate change is undeniable. Emissions reduction alone will not be enough, and we must continue to explore and invest in GGR technologies to complement these efforts. By doing so, we can hope to make meaningful progress in the fight against climate change.