More Than 90 Scientists Write Open Letter Encouraging Study of Geoengineering to Cool Planet

More than 90 scientists from around the world have written an open letter recommending that research be done on the potential of increasing solar radiation modification (SRM) — the reflection of sunlight away from Earth’s atmosphere, sometimes referred to as “solar geoengineering” — in order to slow planetary warming and lessen climate impacts.

The scientists are not endorsing the approach, CNBC reported, as it has the potential for substantial negative effects, such as altering the planet’s systems in unforeseen ways, and would also not address the core issue of climate change: rising fossil fuel emissions and their negative impacts on the climate.

“Climate change is causing devastating impacts on communities and ecosystems around the world, posing grave threats to public health, economic security, and global stability. Natural systems are approaching thresholds for catastrophic changes with the potential to accelerate climate change and impacts beyond humans’ ability to adapt,” the letter states.

The letter’s signatories, who come from institutions like NASA, Columbia University, the Massachusetts Institute of Technology and Harvard University, point out that the only way to limit global warming permanently is to immediately reduce greenhouse gas emissions, reported CNBC.

“While reducing emissions is crucial, no level of reduction undertaken now can reverse the warming effect of past and present greenhouse gas emissions. The Earth is projected to continue to warm for several decades in all of the climate change scenarios considered by the UN’s IPCC,” the letter says.

The scientists do not believe the Paris agreement goal of keeping global heating to “well below” two degrees Celsius compared with pre-industrial levels — ideally below 1.5 degrees — will be met.

“Even with aggressive action to reduce GHG emissions it is increasingly unlikely that climate warming will remain below 1.5-2°C in the near term. This is because reversing current warming trends will require a significant reduction in the atmospheric concentrations of greenhouse gases, which significantly lag behind reductions in emissions due to their long atmospheric lifetime,” the letter states.

Some air pollution particles released by humans have been working to counteract global heating by mixing with clouds and reflecting sunlight away from the planet.

“In contrast to greenhouse gases, another category of emissions from human activities, particulate (aerosol) emissions, can act to cool climate. Aerosols cool climate by scattering sunlight and, when they mix into clouds can increase cloud reflectivity and lifetime,” the letter states.

The scientists go on to say it is estimated that human discharged aerosols are currently offsetting about one-third of the planetary warming from greenhouse gasses.

As greenhouse gas emissions have continued to increase, particulate air pollution regulations have caused aerosol emissions to decrease.

“Because the lifetime of aerosols in the atmosphere is less than a week, reductions in aerosol emissions rapidly reduce this source of climate cooling. As such, reductions in aerosol emissions in the coming few decades will rapidly ‘unmask’ a significant but very uncertain amount of climate warming,” the scientists wrote in the letter.

Technologies to remove atmospheric carbon dioxide are necessary to keep warming below 1.5 degrees Celsius, but are too expensive and difficult to implement under the current climate system, the scientists said.

“Based on analyses of a broad range of feasible greenhouse gas and aerosol emissions scenarios, recent scientific assessments indicate that holding near-term climate warming to below 1.5°C is unlikely without significant carbon dioxide removal from the atmosphere. There are substantial environmental, technical, and cost challenges in using carbon dioxide removal (CDR) at the scale needed to significantly reduce global warming,” the scientists wrote. “While using CDR to remain below 1.5°C may be physically possible, these challenges and the slow response of the climate system make it unlikely that CDR could be implemented rapidly enough or at sufficient scale to entirely avoid dangerous levels of climate warming in the near term.”

The scientists say it is crucial to study these climate adaptation technologies now — using available methods such as small-scale field experiments, analytical studies, computer model simulations and observations — before the situation gets worse.

“While we fully support research into SRM approaches, this does not mean we support the use of SRM. Uncertainties in how SRM implementation would play out in the climate system are presently too large to support implementation… Indeed, we support a rigorous, rapid scientific assessment of the feasibility and impacts of SRM approaches specifically because such knowledge is a critical component of making effective and ethical decisions about SRM implementation,” the scientists said.

They added that not enough is currently known about SRM for it to be used in a “climate credit system.”

“[S]ince SRM does not address the cause of climate change, nor all of the effects of increased greenhouse gas concentrations, it likely will never be an appropriate candidate for an open market system of credits and independent actors,” the scientists wrote in the letter.

The scientists said climate risk must be assessed independently, with and without SRM, so that research findings are shielded from the influence of business interests, politics and pressure from the public.

“Where possible, governments, philanthropists and the scientific community must seek ways to expand scientific capacity for Global South researchers to both engage in and direct research on SRM,” the scientists wrote.

But testing ways to manipulate the climate could hamper efforts to develop regulations for the alternative methods, as well as distract from the necessary rapid reduction of greenhouse gas emissions, said Lili Fuhr, deputy director of the Center for International Environmental Law’s Climate & Energy Program, as Inside Climate News reported. “A United Nations advisory committee to the Human Rights Council is currently working on a report on geoengineering from a human rights perspective. And we hear that some governments are preparing a potential resolution in the U.N. General Assembly on solar geoengineering,” Fuhr said, as reported by Inside Climate News.