Why we need carbon removal

An introduction to negative emissions technologies

Foresight led innovation

Research and Publications


Catastrophic warming is unavoidable without removing carbon
from the atmosphere on a large scale

It is no longer possible to achieve the Paris agreement goal through emissions reductions alone. The slow pace of decarbonisation to date means that even highly ambitious emissions reduction scenarios still result in overshooting 2 degrees of warming. This reality is the driver of the term “net zero”. Net-zero emissions refers to the need to balance out residual emissions with “negative emissions” delivered by carbon removal. Current forecasts indicate global removal of 5-15 billion tonnes of CO2 is needed each year from 2030 to avoid catastrophic warming. This equates to 15% to 40% of the 35 billion tonnes CO2 in global annual emissions reductions required by 2050. These rates of carbon removal are required to offset the residual emissions from slow and difficult to abate industries. While the renewable energy transition has made deep emissions reductions technically feasible and cost effective, we will exceed remaining carbon budgets before we achieve emissions reductions goals.

An illustrated pathway to limit warming to 1.5 degrees by 2100

The chart below outlines an illustrative pathway to limit warming to 1.5 degrees by 2100. This is an ambitious emissions reduction scenario vis-à-vis current national emissions reduction commitments. Even in this ambitious scenario, the 1.5 degree temperature goal is exceeded in the 2030s, before then declining through the implementation of large scale carbon removal to rebalance the climate. Estimated global temperature peaks are shown in blue for the range and red for the mean before returning to safer levels.

It depicts a few key stages:


The lefthand side of the chart shows that there is insufficient time to reduce emissions to net zero before we overshoot greenhouse gas release thresholds to limit warming to 1.5 degrees. This means we will need to pay back the carbon debt that we have accrued. Carbon removal is sometimes relegated as a mechanism for emitters to avoid decarbonising in the short-term but as we can tell from this chart, the more that is avoided now, the more that needs to be paid back in the future. Emitters need to drastically cut emissions as fast as possible AND we need to commence scaled carbon removal to pay back the carbon debt.

Stage One - Meeting a net-zero target for CO2

Global warming roughly stabilises around 2050 as residual CO2 emissions are balanced by an equal amount of CO2 removal. This is shown by the arrows in the Stage One band.

Stage Two - Meeting a net-zero target for all GHG

Global warming peeks then declines in the decades after. Residual CO2 and other GHG emissions are balanced by an equal amount of CO2 removal. This is shown by the arrows in the Stage Two band.

Stage Three - Net-negative GHG emissions to achieve safer temperatures

Global net-negative GHG emissions start to reduce followed by global temperatures allowing the climate to re-balance. Huge volumes of carbon removal are required for decades after net zero. It is for this reason that the net zero imperative has been more accurately characterised as a goal of zero, then negative.

Adapted from: Rogelj e.a, 2021, https://www.nature.com/articles/d41586-021-00662-3


Negative emissions technologies are the pathway to achieve
scaled carbon removal

Negative emissions technologies (NETs) are the technologies that perform carbon removal. NETs capture and store atmospheric CO2 durably and safely over the long term. There have been hundreds of specific NETs identified by researchers.

NETs can be grouped by the process they use – the biological or chemical removal of carbon.

Biological NETs

Use photosynthesis to capture carbon dioxide from the atmosphere and are paired with a durable storage method, such as storage in soils, ocean or living ecosystems.

Chemical NETs

React with CO2 either directly in the air or dissolved in water in the form of carbonic acid.

The choice isn’t either/or

Some remove and store carbon in a single step, others involve separate sequential processes for removal and storage. Some also involve intermediate steps to produce bioproducts of economic value to offset the costs of removals, including carbon utilisation.

The limited popular discourse on atmospheric carbon removal tends to reduce discussion to a choice between the “natural solution” of afforestation or “engineered solutions” of direct air capture or bioenergy with carbon capture and storage. In practice there is a much wider range of approaches to deliver carbon removal, many of which leverage both biological and engineered elements.

Deployment requires a systems perspective

NETs will only deliver help lower atmospheric carbon, if the reliably remove and store more carbon than they result in upstream and downstream in their supply chains.

That’s why we take a systems view of solutions development.

NETs by process

This information table (Minx et al 2018) outlines:

  • categories of NETs currently conceived
  • specific implementation options
  • relevant earth system elements
  • the carbon storage medium.

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Technology category
Afforestation and reforestation (AR)
Soil carbon sequestration (SCS)
Biochar (BC)
Bioenergy with carbon capture and storage (BECCS)
Direct air capture (DACCS)
Enhanced weathering and ocean alkalinisation (EW)
Ocean fertilisation (OF)
Crop residues
Implementation options
Dedicated crops
N and P
Dedicated crops (marginal)
Enhancing upwelling
Earth systems  Land  Ocean
Storage medium  Above-ground biomass Soil   Geological resivours  Minerals  Marine sediment and calcifers
Capture by  Photosynthesis Chemistry   Photosynthesis

Adapted from: (Minx et al 2018)

Most NETs mimic and accelerate the earths carbon removal processes

We can understand more about the job to be done, by taking systems view of the earth’s carbon cycle. Over the lasts century, we have massively accelerated one side of the carbon cycle, primarily through transferring carbon stored under the earth’s surface to carbon dioxide in the atmosphere through mining and combusting fossil fuels. Changes in land use and saturation of carbon dioxide in the Oceans have further reduced the ability of the carbon cycle to remove these emissions.

This process itself is an example of how we’ve mimicked earth’s natural processes – volcanoes too take fossilised carbon from beneath the earth’s surface and release it into the atmosphere as carbon dioxide. In fact, massive persistent volcanic eruptions have previously been responsible for warming the climate. The explosion of huge Siberian volcanoes over millennia are theorised to have contributed to the largest mass extinction event in the earth’s history, the end-Permian, by warming the climate a blistering 10 degrees

But volcanoes also spew silicate rocks onto the earth’s surface. When the rocks cool, they begins to weather – meaning the silicate minerals in the rock react with molecules in the ambient air, notably carbon dioxide. Over millions of years, this weathering process converts carbon dioxide in the atmosphere into mineralised carbon – like bicarbonate. Over thousands of years oceans and new forests historically removed atmospheric carbon, collectively lowering temperatures to create a habitable climate

Most NETs aim to mimic and accelerate aspects of this natural removal cycle, so we can lower atmospheric carbon over decades rather than millions of years to slow then reverse the damage already locked in. Many involve forms of “enhanced weathering” speeding up the mineralisation of carbon with silicate rocks. Others harness the geochemistry of the ocean, to reverse acidification and increase oceans’ ability to remove carbon dioxide. Others still harness photosynthesis of land and aquatic plants to remove and store carbon dioxide in various ways.


Conventional research, development, and demonstration won’t deliver NETs at scale in the time needed

Most NETs are at very low levels of maturity. Some are at concept stage. No NETs have been proven at the gigatonne scale needed.

The study of historical innovations tells us mass adoption of innovation takes 50 years or more from proof of concept. This is because the successful diffusion of new innovations often involves the co-evolution of other innovations across their ultimate supply chains. These interdependencies include the adoption of innovations that support centralised manufacturing, input materials and processes, locally diffuse infrastructure, social norms, markets and governance.

We need an approach that considers ‘interdependencies’ from the start

We know from the IPCC scenarios that we don’t have 50 years to wait for NETs to reach gigaton scale if we are to limit warming to 2°C or lower. To scale NETs in the timeframe required, we need research, development, and demonstration (RD&D) that strategically considers the interdependent technologies, practices, and infrastructure required for end-to-end negative emission supply chains, rather than a fragmented RD&D focus on individual components. This foresight-driven supply chain approach is particularly important for NETs because their ability to deliver negative emissions depends on the net emissions of their supply chains.

We need to facilitate strong collaboration between scientists, engineers, financiers, entrepreneurs, industry, policy makers and the social scientists

Mass adoption of new technology depends on a range of key factors beyond technological readiness. For NETs, key success factors are likely to include the economics of supply, social license, measurement and verification technology, policy settings and the development of relevant technical expertise.

These factors have the capacity to act as enablers or barriers to successful implementation at scale. Thorough research, design, planning and management will be needed to harness these factors to accelerate NETs deployment and ensure that it is aligned with changing economic, social and governance realities. These factors are not ‘set and forget’ – we need to foresight these factors now and continually monitor and respond to developments into the future, and embrace the fact that social license must be earned.


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