What are the most promising and cost-effective NETs for different regions and contexts?

The most promising and cost-effective Negative Emissions Technologies (NETs) are: the Carbon capture and storage (CCS), reforestation, and bioenergy with carbon capture and storage (BECCS) However, the suitability of each NET depends on local conditions, policy frameworks, and technological advancements. Evaluation of specific regional needs and challenges is also essential for determining the most effective NETs.

Bioenergy with Carbon Capture and Storage (BECCS) is a climate change mitigation technology that combines the production of energy from biomass (such as plants and organic materials) with the capture and storage of carbon dioxide (CO2) emissions. By growing biomass that absorbs CO2 as it grows, and then capturing and storing the CO2 produced when the biomass is used to generate energy, BECCS aims to reduce atmospheric CO2 levels, potentially achieving negative emissions. This technology faces challenges, including sustainability of biomass production, land use competition, and the security of CO2 storage, but is considered crucial in many strategies to meet global climate targets.

To realize the potential of BECCS, several pathways must be navigated: - biomass resources must be sustainably managed and harvested. - efficient biomass-to-energy conversion technologies need to be developed and deployed - captured CO2 must be safely transported and stored durably underground

Bioenergy with Carbon Capture and Storage (BECCS) is a process that combines biomass energy production with carbon capture and storage technology. Biomass, such as plants and agricultural waste, is converted into energy, and the resulting CO2 emissions are captured and stored underground. This process can potentially create negative emissions, meaning it removes more CO2 from the atmosphere than it emits. BECCS is considered a crucial technology for achieving net-zero carbon emissions and mitigating climate change. However, its scalability and impact on land use and biodiversity remain significant challenges.

Direct Air Capture (DAC) tech extracts carbon dioxide directly from the atmosphere. While it holds promise for addressing climate change, it faces the inherent issue of being an energy-intensive and costly process, which deems it as arguably a lower order option when compared in a hierarchy against other decarbonisation alternatives which effects direct emission reduction / prevention. Notwithstanding, DAC should not be dismissed yet as various pathways to combat climate change continue to be explored. For example, DAC could potentially be needed to help scale green methanol production for shipping, as production of biogenic CO2 and CCU from other processes may not be sufficient to scale up enough to decarbonise maritime transport.

DACS with geological CO2 storage has several advantages as a carbon dioxide removal approach, including a relatively small land and water footprint, and high degree of assurance in both the permanence of the storage and the quantification of CO2 removed.

Direct Air Capture & Storage (DACS) is a technology designed to tackle climate change by removing carbon dioxide (CO2) directly from the atmosphere and securely storing it underground or utilizing it in various products. DACS targets the broader atmosphere, where CO2 concentrations are much lower, making the process technically challenging but highly valuable for its potential to reduce global warming. The technology typically involves fans or other mechanisms to draw air into a facility, where CO2 is chemically absorbed by a filter or liquid solution. Once captured, the CO2 can be concentrated, purified & then transported for storage in geological formations or used in the production of carbon-neutral fuels, chemicals & other materials.

Direct Air Capture and Storage (DACS) faces significant challenges due to the low concentration of CO2 in the atmosphere, which is around 0.04%. Capturing CO2 at such low concentrations requires substantial energy and advanced materials to efficiently separate it from other atmospheric gases. This makes the process energy-intensive and costly compared to capturing CO2 from more concentrated sources like industrial emissions. Additionally, large-scale deployment of DACS requires significant infrastructure and technological advancements. Overcoming these challenges is crucial for making DACS a viable and sustainable solution for reducing atmospheric CO2 levels.

Combining CGS with EOR in depleted hydrocarbon reservoirs is a cost-effective approach to reduce global warming caused by anthropologic CO2 emissions while a substantial volume of oil can be recovered. However, the presence of oil layer; which are induced as a result of oil migration over geological time frame, coating the inner wall of the pores, significantly impacts fluid distribution and displacements at in the pores which is closely related to the reservoir-scale mechanisms. Furthermore, this alteration in wettability significantly impacts the geostorage capacity and enhanced oil recovery. Thus, it’s of vital importance to take these subsurface physics in the implementation of any CGS-EOR projects.

Enhanced Weathering (EW) is a climate change mitigation strategy that accelerates the natural process of weathering to remove CO2 from the atmosphere. By spreading finely ground silicate rocks over land or into oceans, EW speeds up chemical reactions that convert atmospheric CO2 into carbonate minerals or bicarbonate ions, effectively sequestering carbon in a stable form and potentially reducing ocean acidification. This approach offers a way to permanently lock away atmospheric CO2, but its large-scale feasibility, costs, and environmental impacts are still under investigation.

In Brazil, capturing carbon from sugarcane bagasse and other agricultural by-products is more feasible due to the country's robust agricultural sector. Sugarcane processing produces significant amounts of biomass, which can be converted into energy and have its CO2 emissions captured. This method leverages existing infrastructure and abundant resources, making it more cost-effective than direct air capture. Additionally, Brazil's expertise in bioenergy enhances the efficiency of carbon capture from these sources. Utilizing agricultural residues for carbon capture supports sustainable practices and helps reduce overall greenhouse gas emissions.

Soil Carbon Sequestration (SCS) is a natural process that captures atmospheric carbon dioxide (CO2) and stores it in the soil, leveraging the capacity of plants to absorb CO2 and transfer it to the soil through roots and decomposing organic material. This process not only helps mitigate climate change by reducing atmospheric CO2 levels but also enhances soil health, fertility, and moisture retention. Agricultural practices that promote SCS include no-till farming, cover cropping, applying compost and biochar, rotating crops, and improving grazing management. While offering a sustainable way to combat climate change, the effectiveness of SCS depends on various factors such as soil type, climate, and farming practices.

Afforestation and reforestation (A/R) are critical strategies for increasing forest cover to mitigate climate change, enhance biodiversity, and restore ecosystems. Afforestation involves planting trees on lands that have not been forested for a long time or ever, transforming them into new forests, while reforestation aims to restore forests on lands that have been deforested due to activities like logging or agriculture. These practices contribute to carbon sequestration by absorbing atmospheric carbon dioxide through photosynthesis, offering a natural solution to reducing greenhouse gases.

Afforestation and deforestation are two opposite terms, but they do have some similarities - both afforestation and deforestation are related to trees. Afforestation has a positive impact on the environment, while deforestation has a negative impact. Hence, both processes have a significant impact on the environment. - aforestation involves planting more and more trees, which provide shelter, oxygen, food, and other benefits. On the other hand, deforestation can contribute to industrialization. So both terms can serve human interests. - both terms are performed in forested areas

A variant of afforestation and reforestation is the restoration of coastal and marine habitats. Restoration of mangrove ecosystems come to mind – they are highly efficient carbon sinks which sequester >50% of coastal ecosystems’ carbon while accounting for just 2% of footprint. Beyond climate change mitigation, they contribute to climate adaptation as well - providing natural barriers against storm surges and sea-level rise, reducing erosion, and enhancing coastline resilience. Mangroves are not only a lifeline for the planet, but also offer social co-benefits for local communities as well - they support local fisheries by providing habitats for diverse species and promote coral health by filtering runoff sediments and pollutants.

Planting trees is considered the best solution for carbon capture due to their natural ability to absorb CO2 during photosynthesis. Trees store carbon in their biomass and soil, providing a cost-effective and scalable way to reduce atmospheric CO2 levels. This approach also offers additional environmental benefits, such as improving biodiversity, enhancing soil health, and preventing erosion. Unlike technological solutions, tree planting requires minimal infrastructure and supports ecosystem services. Long-term reforestation and afforestation projects are essential for sustainable carbon sequestration and combating climate change.

Ocean-based Negative Emission Technologies (NETs) encompass various strategies aimed at leveraging the ocean's natural capacity to absorb and store carbon dioxide (CO2), thereby mitigating climate change. These methods include ocean fertilization to boost phytoplankton growth, enhanced weathering to increase seawater's CO2 absorption through mineral dissolution, ocean alkalinization to enhance the ocean's capacity to sequester CO2 by increasing water alkalinity, and artificial upwelling or downwelling to stimulate biological productivity or sequester CO2 in deep waters.

While NETs are often technically advanced and headline grabbing, there are loads of efficiencies to be unraveled just from tightening our current processes aone (often via IoTs). The energy transfer from molecular states to work put to waste approx 74% of the potential energy from thee source - which is why BEV is so much more energy efficiency (from electrons to work). The vast majority of all operations today rely on relatively unsupervised periodic maintenance which can be a problem in terms of maintaining efficiency and uptime - thereby creating more waste. Therefore, while NETs are often technologically fascinating and we definitely need some of those to be commercialised and scale, there're many low hanging fruits too!

Reforestation and afforestation are not = compensation levers for deforestation continuing with unsustainable, heavy emitting industries. While restoring forested areas and creating new ones are both beneficial as they contribute to carbon sequestration, which helps mitigate climate change, they are not the panacea to the root of our climate change issues we face today. Case in point - while reforestation and afforestation help restore and create forests, they cannot fully compensate for the loss of old-growth forests due to deforestation in various way – mature forests are rich in biodiversity and have complex ecosystems that cannot be easily replicated by newly planted forests. Young forests are also less efficient carbon sequestrators.