Terrestrial Carbon Dioxide Removal Research Articles

Relevance of surface albedo to forestry policy in high latitude and altitude regions may be overvalued

Abstract Forest restoration and improved forest management are seen as options to enhance terrestrial carbon dioxide removal in many regions, yet concerns surrounding their potentially adverse surface albedo impacts exist, particularly in high latitude and altitude regions. Such concerns are often based on generalized conclusions rooted in analyses carried out over broad spatial extents at coarse resolutions. The impacts of surface albedo change are highly sensitive to local environmental factors governing both the surface albedo and solar radiation budgets, and many previous assessments either do not sufficiently deal with such sensitivities or do not qualify the conditions under which they are relevant. Using the country of Norway with its diverse gradients in topography and climate as an ideal case study region, we seek clarity to the question of whether surface albedo is relevant to consider in forestry planning, and if so, what are the important factors determining it. We find that the adverse impact of a forest’s albedo outweighs its carbon cycle benefit on only ∼4% of Norway’s total forested area, reducing to <∼1% when future climate changes are considered. Our findings challenge the common perception that surface albedo concerns are highly relevant to forestry planning at high latitudes and emphasize the importance of carrying out albedo impact assessments at spatial scales aligning with those of local forestry planning.

Navigating Potential Hype and Opportunity in Governing Marine Carbon Removal

As the technical and political challenges of land-based carbon dioxide removal (CDR) approaches become more apparent, the oceans may be the new “blue” frontier for carbon drawdown strategies in climate governance. Drawing on lessons learnt from the way terrestrial carbon dioxide removal emerged, we explore increasing overall attention to marine environments and mCDR projects, and how this could manifest in four entwined knowledge systems and governance sectors. We consider how developments within and between these “frontiers” could result in different futures—where hype and over-promising around marine carbon drawdown could enable continued time-buying for the carbon economy without providing significant removals, or where reforms to modeling practices, policy development, innovation funding, and legal governance could seek co-benefits between ocean protection, economy, and climate.

Evaluating the terrestrial carbon dioxide removal potential of improved forest management and accelerated forest conversion in Norway.

As a carbon dioxide removal measure, the Norwegian government is currently considering a policy of large-scale planting of spruce (Picea abies (L) H. Karst) on lands in various states of natural transition to a forest dominated by deciduous broadleaved tree species. Given the aspiration to bring emissions on balance with removals in the latter half of the 21st century in effort to limit the global mean temperature rise to "well below" 2°C, the effectiveness of such a policy is unclear given relatively low spruce growth rates in the region. Further convoluting the picture is the magnitude and relevance of surface albedo changes linked to such projects, which typically counteract the benefits of an enhanced forest CO2 sink in high-latitude regions. Here, we carry out a rigorous empirically based assessment of the terrestrial carbon dioxide removal (tCDR) potential of large-scale spruce planting in Norway, taking into account transient developments in both terrestrial carbon sinks and surface albedo over the 21st century and beyond. We find that surface albedo changes would likely play a negligible role in counteracting tCDR, yet given low forest growth rates in the region, notable tCDR benefits from such projects would not be realized until the second half of the 21st century, with maximum benefits occurring even later around 2150. We estimate Norway's total accumulated tCDR potential at 2100 and 2150 (including surface albedo changes) to be 447 (±240) and 852 (±295)MtCO2 -eq. at mean net present values of US$ 12 (±3) and US$ 13 (±2) per ton CDR, respectively. For perspective, the accumulated tCDR potential at 2100 represents around 8years of Norway's total current annual production-based (i.e., territorial) CO2 -eq. emissions.

Trade-offs for food production, nature conservation and climate limit the terrestrial carbon dioxide removal potential.

Large-scale biomass plantations (BPs) are a common factor in climate mitigation scenarios as they promise double benefits: extracting carbon from the atmosphere and providing a renewable energy source. However, their terrestrial carbon dioxide removal (tCDR) potentials depend on important factors such as land availability, efficiency of capturing biomass-derived carbon and the timing of operation. Land availability is restricted by the demands of future food production depending on yield increases and population growth, by requirements for nature conservation and, with respect to climate mitigation, avoiding unfavourable albedo changes. We integrate these factors in one spatially explicit biogeochemical simulation framework to explore the tCDR opportunity space on land available after these constraints are taken into account, starting either in 2020 or 2050, and lasting until 2100. We find that assumed future needs for nature protection and food production strongly limit tCDR potentials. BPs on abandoned crop and pasture areas (~1,300Mha in scenarios of either 8.0 billion people and yield gap reductions of 25% until 2020 or 9.5 billion people and yield gap reductions of 50% until 2050) could, theoretically, sequester ~100GtC in land carbon stocks and biomass harvest by 2100. However, this potential would be ~80% lower if only cropland was available or ~50% lower if albedo decreases were considered as a factor restricting land availability. Converting instead natural forest, shrubland or grassland into BPs could result in much larger tCDR potentials ̶ but at high environmental costs (e.g. biodiversity loss). The most promising avenue for effective tCDR seems to be improvement of efficient carbon utilization pathways, changes in dietary trends or the restoration of marginal lands for the implementation of tCDR.

The limits to global‐warming mitigation by terrestrial carbon removal

AbstractMassive near‐term greenhouse gas emissions reduction is a precondition for staying “well below 2°C” global warming as envisaged by the Paris Agreement. Furthermore, extensive terrestrial carbon dioxide removal (tCDR) through managed biomass growth and subsequent carbon capture and storage is required to avoid temperature “overshoot” in most pertinent scenarios. Here, we address two major issues: First, we calculate the extent of tCDR required to “repair” delayed or insufficient emissions reduction policies unable to prevent global mean temperature rise of 2.5°C or even 4.5°C above pre‐industrial level. Our results show that those tCDR measures are unable to counteract “business‐as‐usual” emissions without eliminating virtually all natural ecosystems. Even if considerable (Representative Concentration Pathway 4.5 [RCP4.5]) emissions reductions are assumed, tCDR with 50% storage efficiency requires >1.1 Gha of the most productive agricultural areas or the elimination of >50% of natural forests. In addition, >100 MtN/yr fertilizers would be needed to remove the roughly 320 GtC foreseen in these scenarios. Such interventions would severely compromise food production and/or biosphere functioning. Second, we reanalyze the requirements for achieving the 160–190 GtC tCDR that would complement strong mitigation action (RCP2.6) in order to avoid 2°C overshoot anytime. We find that a combination of high irrigation water input and/or more efficient conversion to stored carbon is necessary. In the face of severe trade‐offs with society and the biosphere, we conclude that large‐scale tCDR is not a viable alternative to aggressive emissions reduction. However, we argue that tCDR might serve as a valuable “supporting actor” for strong mitigation if sustainable schemes are established immediately.

More diverse benefits from timber versus dedicated bioenergy plantations for terrestrial carbon dioxide removal

More diverse benefits from timber versus dedicated bioenergy plantations for terrestrial carbon dioxide removal

Collateral transgression of planetary boundaries due to climate engineering by terrestrial carbon dioxide removal

Abstract. The planetary boundaries framework provides guidelines for defining thresholds in environmental variables. Their transgression is likely to result in a shift in Earth system functioning away from the relatively stable Holocene state. As the climate system is approaching critical thresholds of atmospheric carbon, several climate engineering methods are discussed, aiming at a reduction of atmospheric carbon concentrations to control the Earth's energy balance. Terrestrial carbon dioxide removal (tCDR) via afforestation or bioenergy production with carbon capture and storage are part of most climate change mitigation scenarios that limit global warming to less than 2 °C. We analyse the co-evolutionary interaction of societal interventions via tCDR and the natural dynamics of the Earth's carbon cycle. Applying a conceptual modelling framework, we analyse how the degree of anticipation of the climate problem and the intensity of tCDR efforts with the aim of staying within a "safe" level of global warming might influence the state of the Earth system with respect to other carbon-related planetary boundaries. Within the scope of our approach, we show that societal management of atmospheric carbon via tCDR can lead to a collateral transgression of the planetary boundary of land system change. Our analysis indicates that the opportunities to remain in a desirable region within carbon-related planetary boundaries only exist for a small range of anticipation levels and depend critically on the underlying emission pathway. While tCDR has the potential to ensure the Earth system's persistence within a carbon-safe operating space under low-emission pathways, it is unlikely to succeed in a business-as-usual scenario.

Impacts devalue the potential of large-scale terrestrial CO2 removal through biomass plantations

Large-scale biomass plantations (BPs) are often considered a feasible and safe climate engineering proposal for extracting carbon from the atmosphere and, thereby, reducing global mean temperatures. However, the capacity of such terrestrial carbon dioxide removal (tCDR) strategies and their larger Earth system impacts remain to be comprehensively studied—even more so under higher carbon emissions and progressing climate change. Here, we use a spatially explicit process-based biosphere model to systematically quantify the potentials and trade-offs of a range of BP scenarios dedicated to tCDR, representing different assumptions about which areas are convertible. Based on a moderate CO2 concentration pathway resulting in a global mean warming of 2.5 °C above preindustrial level by the end of this century—similar to the Representative Concentration Pathway (RCP) 4.5—we assume tCDR to be implemented when a warming of 1.5 °C is reached in year 2038. Our results show that BPs can slow down the progression of increasing cumulative carbon in the atmosphere only sufficiently if emissions are reduced simultaneously like in the underlying RCP4.5 trajectory. The potential of tCDR to balance additional, unabated emissions leading towards a business-as-usual pathway alike RCP8.5 is therefore very limited. Furthermore, in the required large-scale applications, these plantations would induce significant trade-offs with food production and biodiversity and exert impacts on forest extent, biogeochemical cycles and biogeophysical properties.

Is extensive terrestrial carbon dioxide removal a ‘green’ form of geoengineering? A global modelling study

Biological carbon sequestration through implementation of biomass plantations is currently being discussed as an option for climate engineering (CE) should mitigation efforts fail to substantially reduce greenhouse gas emissions. As it is a plant-based CE option that extracts CO2 from the atmosphere, it might be considered a ‘green’ CE method that moves the biosphere closer to its natural, i.e. pre-Neolithic, state. Here, we test this hypothesis by comparing the biogeochemical (water- and carbon-related) changes induced by biomass plantations compared to those induced by historical human land cover and land use change. Results indicate that large-scale biomass plantations would produce a biogeochemical shift in the terrestrial biosphere which is, in absolute terms, even larger than that already produced by historical land use change. However, the nature of change would differ between a world dominated by biomass plantations and the current world inheriting the effects of historical land use, highlighting that large-scale tCDR would represent an additional distinct and massive human intervention into the biosphere. Contrasting the limited possibilities of tCDR to reduce the pressure on the planetary boundary for climate change with the potential negative implications on the status of other planetary boundaries highlights that tCDR via biomass plantations should not be considered a ‘green’ CE method but a full scale engineering intervention.