Perspective
What Does 2024’s Breach of 1.5°C Mean for SRM?
Experts react to 2024 being the first calendar year to breach 1.5°C of warming and consider how this could affect the discussion around sunlight reflection methods, also known as solar radiation modification (SRM).
The World Meteorological Organization has confirmed that 2024 was the first calendar year to exceed 1.5°C warming, temporarily breaching a critical international climate goal.
In the 2015 Paris Agreement, countries agreed to pursue efforts “to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change”.
“2024 is the warmest year on record, based on six international datasets”, the WMO said. “The global average surface temperature was 1.55°C (with a margin of uncertainty of ±0.13°C) above the 1850-1900 average … This means that we have likely just experienced the first calendar year with a global mean temperature of more than 1.5°C above the 1850-1900 average.”
We asked four experts how this news might affect the discussion around SRM. These were their thoughts.
Govindasamy Bala
Professor at the Centre for Atmospheric and Oceanic Sciences India
Indian Institute for Science
Govindasamy Bala is a Professor at the Indian Institute of Science. His main research interests are modelling climate change, carbon and water cycles, solar geoengineering, and the global and regional monsoon systems. He has published over 130 peer-reviewed papers and has served as a Lead and Contributing Author in the AR5 and AR6 IPCC WG1 reports.
Govindasamy Bala
Professor at the Centre for Atmospheric and Oceanic Sciences India
Indian Institute for Science
Govindasamy Bala is a Professor at the Indian Institute of Science. His main research interests are modelling climate change, carbon and water cycles, solar geoengineering, and the global and regional monsoon systems. He has published over 130 peer-reviewed papers and has served as a Lead and Contributing Author in the AR5 and AR6 IPCC WG1 reports.
Govindasamy Bala
Professor at the Centre for Atmospheric and Oceanic Sciences India
Indian Institute for Science
Govindasamy Bala is a Professor at the Indian Institute of Science. His main research interests are modelling climate change, carbon and water cycles, solar geoengineering, and the global and regional monsoon systems. He has published over 130 peer-reviewed papers and has served as a Lead and Contributing Author in the AR5 and AR6 IPCC WG1 reports.
Crossing 1.5°C in a single year does not technically mean we have breached the Paris temperature target. As per the IPCC reports, the mean over a 20-year period should be above 1.5°C to declare that we crossed the target. Therefore, we have some more years or decades. Nevertheless, the danger of severe climate change impacts and the potential for crossing the tipping points for some of the key components of the Earth systems, such as tropical and boreal forests and permafrost, are increasing with each passing year.
With net-zero emissions not in sight, the case for research into solar geoengineering is only getting stronger. If there is ever a planetary crisis – a vaguely defined low-probability but high-impact crisis that is attributable to climate change – solar geoengineering is the only option that humanity can rely on to cool the planet rapidly. Thus, solar geoengineering is an option that we may never use but we should study.
Cynthia Scharf
Senior Fellow
Center for Future Generations
Cynthia Scharf is a senior fellow at the Center for Future Generations, a European think tank, leading their work on climate intervention technologies. She was senior strategy director for the Carnegie Climate Governance (C2G) Initiative, and served in the Office of the UN Secretary-General as the head of strategic climate communications and chief speechwriter on climate change.
Cynthia Scharf
Senior Fellow
Center for Future Generations
Cynthia Scharf is a senior fellow at the Center for Future Generations, a European think tank, leading their work on climate intervention technologies. She was senior strategy director for the Carnegie Climate Governance (C2G) Initiative, and served in the Office of the UN Secretary-General as the head of strategic climate communications and chief speechwriter on climate change.
Cynthia Scharf
Senior Fellow
Center for Future Generations
Cynthia Scharf is a senior fellow at the Center for Future Generations, a European think tank, leading their work on climate intervention technologies. She was senior strategy director for the Carnegie Climate Governance (C2G) Initiative, and served in the Office of the UN Secretary-General as the head of strategic climate communications and chief speechwriter on climate change.
This is a tragedy and a betrayal from any perspective: humanitarian, first and foremost, but also environmental, geopolitical, and ethical. We are now in uncharted territory, and must face the world as it is, not as we hoped it would be in Paris. We must do everything scientists told us to do 30 years ago, but those of us in the industrialized North failed to take seriously. We must consider very soberly how we are going to save lives and prevent further suffering – especially for the most vulnerable – as the planet continues to heat up.
SRM is a technology born of desperation. It is not a solution or a substitute for decarbonizing the global economy. At best it might be a supplement to ease some immediate suffering this century. But it has huge unknowns and risks. Humanity may not be capable of equitably governing such a powerful tool. Right now we have more questions than answers, and need to know more. Humility must be our watchword.
Claudia Wieners
Assistant Professor at the Institute for Marine and Atmospheric Research
Utrecht University
Claudia Wieners obtained her PhD in climate physics in 2018 from Utrecht University. After a stint in climate economics, she returned to Utrecht to work on the effects of stratospheric aerosol injection on the climate. She was the lead author of an open letter arguing for a more balanced debate on SRM, which was signed by over 100 scholars.
Claudia Wieners
Assistant Professor at the Institute for Marine and Atmospheric Research
Utrecht University
Claudia Wieners obtained her PhD in climate physics in 2018 from Utrecht University. After a stint in climate economics, she returned to Utrecht to work on the effects of stratospheric aerosol injection on the climate. She was the lead author of an open letter arguing for a more balanced debate on SRM, which was signed by over 100 scholars.
Claudia Wieners
Assistant Professor at the Institute for Marine and Atmospheric Research
Utrecht University
Claudia Wieners obtained her PhD in climate physics in 2018 from Utrecht University. After a stint in climate economics, she returned to Utrecht to work on the effects of stratospheric aerosol injection on the climate. She was the lead author of an open letter arguing for a more balanced debate on SRM, which was signed by over 100 scholars.
1.5 is just a number. We don’t know exactly where climate change becomes “too bad”. Every tenth of a degree counts.
With SRM, global mean surface temperature is insufficient to characterize the climate. 1.5°C achieved through high SRM against high CO2 is a different world than 1.5°C achieved by mitigation, both climatically and politically.
Still, we are approaching tipping points, and we already see ever-worsening climate impacts. Even stringent mitigation may not suffice to prevent disaster – SRM might, but governance mechanisms for fair decision-making are lacking. This tension is dangerous, especially in the current political climate.
We must guard against SRM being abused rhetorically, e.g. by fossil companies. Mitigation remains the safest way to reduce climate change. Every ton of CO2 mitigated reduces climate risks – either from global warming or by reducing the amount of SRM (deemed) necessary.
A livable planet may not be achieved through technology alone – be that solar cells or solar geoengineering. A future within planetary boundaries, yet with sufficient means for all to live free of poverty, requires an overhaul of economic thinking, stressing fairness, sufficiency, and redistribution over profit maximization. SRM is just one piece of the puzzle. It should be treated with humbleness.
Simone Tilmes
Project Scientist III
National Center for Atmospheric Research
Simone Tilmes is a Project Scientist III at the National Center for Atmospheric Research (NCAR) and the co-chair for the Community Earth System Model (CESM) chemistry-climate working group. Her scientific interests cover chemical, aerosol, and dynamical processes in chemistry-climate models, as well as the impacts of climate interventions.
Simone Tilmes
Project Scientist III
National Center for Atmospheric Research
Simone Tilmes is a Project Scientist III at the National Center for Atmospheric Research (NCAR) and the co-chair for the Community Earth System Model (CESM) chemistry-climate working group. Her scientific interests cover chemical, aerosol, and dynamical processes in chemistry-climate models, as well as the impacts of climate interventions.
Simone Tilmes
Project Scientist III
National Center for Atmospheric Research
Simone Tilmes is a Project Scientist III at the National Center for Atmospheric Research (NCAR) and the co-chair for the Community Earth System Model (CESM) chemistry-climate working group. Her scientific interests cover chemical, aerosol, and dynamical processes in chemistry-climate models, as well as the impacts of climate interventions.
After Paul Crutzen’s paper in 2006, another significant increase in interest in SRM came after the Paris Agreement 2015, which defined the temperature goals of 1.5 and 2°C. With this, the so-called “SAI peak-shaving scenario” became meaningful since it illustrated an option to keep surface temperatures from crossing specific thresholds even if mitigation efforts were insufficient. The announcement of breaching 1.5°C above pre-industrial conditions may be another milestone that will increase interest in this topic.
However, the steadily worsening impacts of climate change around the world and the limited progress on emissions cuts so far have strongly increased the interest in unconventional climate policy options in recent years. At this time, the prospects for developing a well-coordinated global SAI program to reduce the effects of global warming will remain dim until research and governance efforts have substantially advanced.
The views expressed by Perspective writers and contributors are their own and are not necessarily endorsed by SRM360. The goal of our Perspectives is to present ideas from diverse viewpoints, further supporting informed discussion of sunlight reflection methods.
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