The UK government is committed to delivering net zero and tackling the underlying causes of climate change.
However, as climate impacts increase globally, there is increased attention on radical intervention measures to control temperatures, including SRM, a process in which some radiation from the Sun is reflected back into space.
Computer modelling possible outcomes
There is currently insufficient knowledge of the impact these interventions might have on the Earth’s system if they are ever deployed at scale, and how this would affect regional climate, humans and ecosystem.
There are also uncertainties around the effectiveness of some proposed SRM approaches.
Improving our knowledge
The Natural Environment Research Council (NERC) will invest £10 million in four research projects, launching in April, that aim to address these gaps in our understanding.
These projects will not deploy SRM in the real world.
Using only computer modelling research and historical data-drive research, the five-year studies will investigate the impact of the following.
Stratospheric aerosol intervention
This is the process of adding particles into the atmosphere that will reflect the Sun’s rays.
Marine cloud brightening (MCB)
This technique aims to increase the reflectivity of clouds over the ocean by spraying sea water to create more cloud condensation nuclei.
Environment’s response to SRM
They will examine how the environment might respond to SRM by comparing it to real world natural analogues such as volcanic eruptions and changes in shipping emissions.
Cooling potential of four lesser-known SRM approaches
This includes the three focused on solar or terrestrial radiation and one examining the use of tiny, rod-like nanoparticles (cellulose nanocrystals) derived from natural cellulose sources to enhance the effectiveness of stratospheric aerosol intervention.
Public dialogue
The programme aligns with the UK government’s position on SRM, in that the UK is not deploying SRM and has no plans to do so. The UK continues to invest in modelling studies to better understand the impacts of SRM deployment.
The research aims to deliver independent risk-risk analyses to inform policymakers on the potential environmental impacts of SRM.
NERC, with support from Sciencewise, is also commissioning a public dialogue to engage a diverse group and understand what public views and considerations are on SRM.
Considering the ethics of SRM
Professor Louise Heathwaite, Executive Chair of NERC, said:
NERC invests in a wide range of research to tackle, adapt to, and mitigate climate change. The UK’s priority is to tackle the root cause of climate change by reducing emissions of greenhouse gases from human activities and adapting to those impacts that are unavoidable.
However, with the increased interest internationally in solar radiation modification measures, there is a pressing need to consider the impact of SRM approaches to control Earth system temperature. These research projects will analyse these approaches in detail and address ethical and governance considerations.
Further information
Details of the projects awarded funding
The studies are part of NERC’s Modelling environmental responses to solar radiation management programme.
Advancing holistic risk assessment for measures to address climate change
Partners include:
- Imperial College London
- University of Bristol
- University of Leeds
- University of Exeter
Stratospheric aerosol injection (SAI) is a potential way to reduce global temperature increases from greenhouse gas emissions by reflecting sunlight. While it might mask some global warming its risks and potential effects, including on global society, are not well understood. This project aims to address that by looking at two main challenges.
First, SAI’s effects on droughts, air quality and extreme weather might differ from those of reducing greenhouse gas concentrations. Research is needed to understand these physical impacts and their global distribution.
Second, studies often focus on SAI’s physical effects while neglecting social, political and economic factors, leading to incomplete risk assessments.
The project proposes a new framework combining risk analysis with Earth system modelling.
By focusing on key scenarios and their physical impacts while also exploring how the possibility of SAI might affect future decision making, researchers can better assess its:
- risks and benefits alongside other climate measures
- potential implications for those measures
This will provide more comprehensive and policy relevant information for future climate decisions.
Marine CLOUD Brightening (MACLOUD)
Partners include:
- University of Exeter
- University of Leeds
- University of Reading
- The University of Manchester
- University of Oxford
MACLOUD aims to model the potential of MCB to combat climate change. MCB proposals involve spraying seawater to create tiny sea-salt particles that brighten clouds, reflecting more sunlight and cooling the planet. However, the effectiveness and impacts of MCB are uncertain.
To understand MCB’s effects, MACLOUD will use various models to simulate the process from small-scale aerosol formation to large-scale climate impacts to simulate how aerosols evolve, form cloud droplets, and influence cloud behaviour and weather patterns.
The project will also consider different climate scenarios and deployment strategies to assess MCB’s potential benefits and risks.
By integrating results from detailed aerosol and cloud models with global climate models, MACLOUD aims to provide a comprehensive understanding of MCB’s feasibility and its role in mitigating climate change. The project will also study how MCB might affect critical Earth systems like the Amazon, crop productivity and sea-ice.
Quantifying efficacy and risks of solar radiation management approaches using natural analogues (QUESTION)
Partners include:
- University of Birmingham
- University of Edinburgh
- Center for International Climate and Environmental Research, Norway
NASA and the UK Met Office have confirmed that 2024 was the first year that global temperatures reached +1.5°C higher than pre-industrial levels.
While a temperature rise of 1.5°C for a single year doesn’t mean that we have breached our commitments under the Paris Agreement (as global warming is an average over decades), it is a strong warning signal that we are getting closer.
To address this, some countries are considering SRM methods to artificially cool the Earth by reflecting more sunlight back into space, buying time for global decarbonisation.
The main SRM methods are:
- SAI, which creates a protective aerosol layer
- MCB, which increases cloud reflectivity over oceans
While these methods could slow warming, their effectiveness and side effects, such as ozone depletion and altered weather patterns, are uncertain.
The QUESTION project aims to study SRM using natural analogues like volcanic eruptions and changes in ship emissions. It will address challenges in mimicking SRM effects, separating SRM signals from other factors, and improving climate models.
This research will help assess SRM’s risks and benefits, supporting informed climate action.
Evaluation of Climate Intervention through novel Potential Strategies (ECLIPSE)
Partners include:
- University of Cambridge
- University of Exeter
- Imperial College London
This research will evaluate the climatic impacts of four SRM approaches, including cellulose nanocrystals (CNCs) for SAI. The project will assess these methods across various temperature scenarios, including the critical 1.5˚C goal, analysing their effects on radiative forcing, temperature changes and associated risks.
Using earth system models, the project will explore the cooling potential of each SRM approach.
Work package one will focus on reducing uncertainty in cloud thinning for cooling by integrating observational data to refine climate model simulations.
Work package two will assess the regional cooling effects of marine sky brightening over the Mediterranean Sea.
Work package three will evaluate the impact of sea ice flooding on climate dynamics.
Work package four will study the effects of CNCs for SRM.
The final work package will integrate findings into a comprehensive report, providing actionable recommendations and risk assessments for SRM approaches, guiding informed climate intervention decisions.
This will also draw upon outputs from the other projects funded by NERC.
Programme background
Why are you funding this programme?
Climate change from continued emissions of greenhouse gases has led to severe impacts to people and nature, including extreme weather events such as floods, heatwaves and droughts.
As a result, there is increased attention in radical intervention measures to control temperatures, including SRM, a process in which the Sun’s rays are artificially reflected back into space.
There is currently insufficient knowledge of the impact these interventions might have on the Earth’s system, if they were ever deployed at scale.
Are you deploying SRM to test the approaches?
No SRM will be deployed as part of this research.
Are you supporting giving up on mitigating climate change through actively reducing greenhouse gas emissions and instead supporting SRM?
No. NERC and UK Research and Innovation (UKRI) are investigating in a wide range of research focused mainly on tackling, adapting to and mitigating climate change.
Our priority is to tackle the root cause of climate change by supporting research that reduces emissions of greenhouse gases from human activities and adapts to those impacts that are unavoidable.
The SRM investment recognises that there is increased interest in SRM measures suggesting that there is a pressing need to consider the impact of SRM approaches to control Earth system temperature.
Are you linked to Advanced Research and Invention Agency’s (ARIA) work on Exploring Climate Cooling?
NERC’s funded research is distinct from the work of ARIA and has been developed and delivered independently.
NERC and ARIA are ensuring that there is no duplication in funding between their investments.
How can the public take part or give their opinions on this research programme?
NERC, with support from Sciencewise, is commissioning a public dialogue as part of the broader investment in the SRM programme.
The aim of this is to engage a diverse group of the UK public to deliberate on SRM to understand what public views and considerations are on SRM.
This will include social, legal and ethical issues bound up with both research and potential deployment of SRM. This information gathered will be relevant and inform a broad audience including a range of decision makers, researchers and UKRI.
When will the research programme start?
The research projects will start in April 2025.
The public dialogue will happen in the latter half of 2025 and into the beginning of 2026.
What ethical guidance and governance is in place to manage any risks around SRM research or this programme?
The programme aligns with the government position on geoengineering, including SRM, which is that the UK is not deploying SRM and has no plans to do so.
The UK government has commissioned modelling research to better understand the risks and impacts of SRM, and monitors research in this area.
The researchers funded in this programme will be expected to consider the implications for ethics, governance and regulation from the research of the programme, working with wider stakeholders and experts in this field of research.
The public dialogue to be funded as part of this programme will engage a diverse group of the UK public to deliberate on SRM to understand what public views and considerations are on SRM. This includes social, legal and ethical issues bound up with both research and potential deployment of SRM.
Research projects are required to be delivering research that supports the Oxford Principles, five high-level principles for geoengineering governance.
Will research data be made available?
All data will be made publicly available as per usual NERC funding rules.
Research projects will be required to be delivering research that supports the Oxford Principles, five high-level principles for geoengineering governance.
In particular this relates to principle three: disclosure of geoengineering research and open publication of results, whereby:
“There should be complete disclosure of research plans and open publication of results in order to facilitate better understanding of the risks and to reassure the public as to the integrity of the process. It is essential that the results of all research, including negative results, be made publicly available”.
What is the difference between solar radiation management and SRM? Why have you used both?
As this area evolves, NERC takes advice on the appropriate language to use.
Although there is strictly no difference in meaning between the two, the IPCC (Intergovernmental Panel on Climate Change) are now using ‘modification’, and therefore NERC is moving to use this terminology to ensure consistency.