Effective carbon dioxide removal requires a One-Earth approach

Environmental Research Letters, Volume 20, Number 11
Published 31 October 2025

By Philip W Boyd*, Jean-Pierre Gattuso, Louis Legendre, Yiannis Moustakis and Julia Pongratz

1. Introduction

The only way to reach net-zero greenhouse gas (GHG) emissions within decades is to implement rapid, deep and sustained reductions of global CO2 emissions and other GHG. The IPCC explains that, in addition, carbon dioxide removal (CDR) will be needed to offset residual CO2 emissions from sectors that are difficult and/or costly to decarbonize fully (Arias et al 2021). CDR also has a role to play in insuring against unexpected outcomes from warming overshoot trajectories (Schleussner et al 2024). Required CDR each year is estimated to range from 4.0 (i.e. reduced global energy demand scenario) to 5.9 Gt CO2 (rapid implementation of renewables scenario) in 2030, increasing to 5.3 (reduced global energy demand) and 10.4 (focus on CDR scenario)7 Gt CO2 annually by 2050 (Lamb et al 2024), equivalent to up to 25% of current annual anthropogenic emissions. This Perspective argues for the need to accelerate CDR research, within the new ‘One-Earth’ framework proposed below. It does not address the acceptability or not of deploying CDR as our objective is instead to propose a framework within which to conduct studies that will provide the society and decision-makers with scientific information about the potential positive and negative consequences of proposed CDR techniques. Research should address not only the characteristics of the different proposed CDR methods but also their potential biogeochemical, biophysical and other side effects (table 5.9 and figure 5.36 in Canadell et al 2021). The governance aspect of future CDR deployments is not examined below as it is treated in Boyd et al (2025).

The Perspective discusses successively the need to incorporate Earth System feedbacks (CDR tax8) into CDR studies, the current and projected CDR, the CDR tax in the dynamic Earth System, and CDR efficiency and the CDR tax under Earth system scenarios, to conclude with recent insights on the complexities that emerge when a portfolio of CDR approaches is modeled, including policy aspects. The early recognition of the need to incorporate Earth System feedbacks in CDR studies has its roots in the early concepts of atmosphere and ocean and atmosphere and land being systems exchanging CO2 in both directions (Keeling 1973), which subsequently found its way into coupled (ocean) models (Maier-Reimer and Hasselmann 1987). Climate and carbon cycle feedbacks have since been routinely assessed for land and ocean (Friedlingstein et al 2006, Canadell et al 2021). It has been known for over a decade (Cao and Caldeira 2010) and also recognized by the IPCC (Ciais et al 2013) that CDR-driven carbon influxes into one reservoir would lead to counterbalancing (feedback) effluxes from all Earth’s reservoirs. This negative feedback in the Earth System’s carbon cycle, which is recognized by the CDR modeling community (Jones et al 2016, Keller et al 2018), weakens the realized atmospheric CO2 reduction compared with the expected CDR influx. Because of this tight connection between land, ocean and atmosphere (Zickfeld et al 2023), the combined land- and ocean-based CDR required to reach the annual multi-billion ton target must be studied, financed, and managed as a ‘One-Earth CDR9’.

However, the dependence of feedback strength on the background emissions scenario is not generally considered in the discussion of CDR deployment, nor is the added complication of singling out feedbacks from CDR fluxes when land- and ocean-based CDR are applied at the same time. A holistic viewpoint is needed as current CDR approaches, whether conventional or novel (Geden et al 2024), are mostly discrete and hence unconnected, whereas the Earth System imposes a ‘tax’ on the cumulative effect of all CDR methods that we term ‘CDR tax’ and must be considered in both emerging CDR markets and national carbon accounting. The CDR tax is the fraction of the atmospheric carbon captured by a CDR deployment that is not reflected in the corresponding decrease in atmospheric CO2. For example, a CDR deployment capturing 1.0 Gt CO2 year−1—and causing effluxes of 0.2 Gt CO2 year−1 levies a 20% CDR tax on the Earth System.

Conventional land-based CDR are dominant in current and planned applications (Nemet et al 2024, Pongratz et al 2024), but studying a portfolio that also includes ocean-based CDR is essential for two reasons: first, it shares the heavy lifting imposed by CDR on sustainability limits between the land and the ocean; and second, it is useful to have a portfolio of CDR methods with different dynamics and durations. Indeed, for CDR to have a long-term effect on the climate, the CO2 storage period should be at least 1000 years (Brunner et al 2024). Deploying such a portfolio requires the One-Earth approach, which takes into account the CDR tax.