The Uncharted Territory of the Anthropocene Climate
How much carbon must be removed to prevent too much global warming? Is it possible to alter the Earth’s energy balance by managing incoming solar radiation? These are some of the questions addressed in the NAVIGATE project.
Publisert 08. April 2025
Sunrise by the camera of a satellite. Photo: Freepik/ NASA
If you read a lot about climate change, you might have come across the terms CDR and SRM. These stand for Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM).
Launching the Navigate-project, researchers from NORCE & BCCR, CICERO and the Norwegian Meteorological institute will investigate the climate system’s responses to the use of CDR and SRM.
“This will be the first time a research project simulates the interactions between emission reductions, large-scale carbon dioxide removal and solar radiation management in a fully interactive Earth system model, thereby producing a policy-relevant integrated understanding of how the Earth system respond to a future with 1.5°-2°C warming”, says project leader Jerry Tjiputra, researcher at NORCE and the Bjerknes Centre.
Feasible Emission Reduction Strategies
Behind the Paris Agreement on keeping global warming well below two degrees above pre-industrial levels is the fear of this being a critical threshold. Additional warming above two degrees might lead to dangerous and potentially irreversible cascading effects of climate change for future generations.
Despite the Paris Agreement, countries worldwide are on a path where the target is slipping out of reach. Without rapid global decarbonization within the next few decades, the Paris Agreement target will not be realized, according to the IPCC report on 1.5°C.
With this background, the researchers behind the new NAVIGATE project will consider emission reduction strategies combined with feasible CDR and SRM deployments up to the year 2300.
Climate Models as a Laboratory
The project team will utilize the new version of the Norwegian Earth System model (NorESM3). According to Jerry Tjiputra, the climate model features “advanced representations and interactions between various physical and biogeochemical components in the Earth System”, being one of the few models capable of performing climate projections with a fully interactive carbon cycle.
Tjiputra highlights the model as an ideal tool because it:
- Includes the Greenland icesheet
- Has a demographically enabled terrestrial vegetation and represents permafrost carbon
- Incorporates the latest improvements in ocean biogeochemistry and atmospheric chemistry
Together, these features allow for:
- A more realistic implementation of CDR, with respect to ocean alkalinization, afforestation/reforestation, and BECCS (Bioenergy with Carbon Capture and Storage)
- A quantification of the associated Earth system impacts, including scenario-dependent carbon sequestration efficiency
The NorESM has previously been applied to study various SRM scenarios and their respective climate impacts. Through the NAVIGATE project, “the experiments will be performed in CO2 emissions-driven mode, allowing for accurate estimates of the global carbon budget that includes non-linear feedback across atmosphere, ocean, land, and cryosphere”, as stated by the research team.
Glossary - NAVIGATE
Earth system model: A coupled atmosphere–ocean general circulation model (AOGCM) in which a representation of the carbon cycle is included, allowing for interactive calculation of atmospheric carbon dioxide (CO2) or compatible emissions. Additional components (e.g., atmospheric chemistry, ice sheets, dynamic vegetation, nitrogen cycle, but also urban or crop models) may be included.
SRM: A range of radiation modification measures not related to greenhouse gas (GHG) mitigation that seek to limit global warming. Most methods involve reducing the amount of incoming solar radiation reaching the surface, but others also act on the longwave radiation budget by reducing optical thickness and cloud lifetime.
CDR: Anthropogenic activities removing carbon dioxide from the atmosphere and storing it in geological, terrestrial, or ocean reservoirs, or in products. It includes existing and potential anthropogenic enhancement of biological or geochemical CO2 sinks and direct air carbon dioxide capture and storage but excludes natural CO2 uptake not directly caused by human activities.
BECCS: Carbon dioxide capture and storage (CCS) technology applied to a bioenergy facility. Note that depending on the total emissions of the BECCS supply chain, carbon dioxide (CO2) can be removed from the atmosphere.
Ocean Alkalinization: A proposed CDR method that involves deposition of alkaline minerals or their dissociation products at the ocean surface. This increases surface total alkalinity, and may thus increase ocean carbon dioxide (CO2) uptake and ameliorate surface ocean acidification.
Source: IPCC ipcc.ch/glossary
When Carbon Sinks Become Carbon Sources
The project team has identified several uncertainties and knowledge gaps in the climate system. One of them is the carbon cycle itself.
“Today the ocean and land biosphere are important natural buffers for anthropogenic climate change through absorbing excess CO2 from the atmosphere. However, the current land and ocean carbon sinks will decline or even become a source in the future, exacerbating the difficulty of meeting climate targets”, Jerry Tjiputra highlights.
In the ocean, the carbon sink is weakened due to the expected slowdown of the overturning circulation, which is crucial to export anthropogenic carbon from the surface to the deep ocean, together with lower CO2 solubility and buffer capacity as the ocean absorbs more carbon.
Over land, several processes might compromise the effect of vegetation carbon sink. Additionally, thawing permafrost can add a burden to the global carbon budget.
“The interplay between emission reductions, CDR, and SRM with these underlying global carbon cycle processes is largely unknown and difficult to predict given the complex non-linear interactions between them”, the researchers state in the project description.
In general, the polar regions, and especially the Arctic, are areas where climate change is unfolding at an unprecedented rate – twice as fast as the global average.
Tjiputra and colleagues identify the need for a thorough assessment of Arctic climate change under future 1.5°-2°C warming scenarios, including the regional implications of geoengineering in comparison to emission reductions.
Furthermore, the project will “investigate the generational legacies of anthropogenic climate change and climate interventions globally and in the highly vulnerable polar regions”.
