The Great Geoengineering Divide
Some scientists, including Ricke, as well as some environmentalists, political officials, and business leaders now call for tests of geoengineering technologies that could artificially cool the planet. But this isn’t your typical academic debate over footnotes and methodology. All that attention has added fuel to the smoldering disagreements among climate scientists, creating what is likely the most significant rift in the world’s climate research community. Throughout that time, the idea has remained contentious among environmental groups and large swaths of the public. “I think the very well-founded anxiety about experiments like this is what they will lead to next and next and next,” warns Katharine Ricke from UC San Diego. But in the first three months of 2025, over 16 states have introduced bills to ban solar geoengineering; a Tennessee ban on the technology passed into law in 2024. Many of the states considering such legislation are Republican-led, including Texas and Florida, revealing how deeply the scientific community has fractured. The stakes couldn’t be higher—we’re essentially arguing about whether to redesign the planet’s thermostat.
When Leading Scientists Can’t Agree on Basic Temperature Targets
James Hansen of Columbia University in the US published a paper with colleagues in November which claims temperatures are set to rise further and faster than the predictions of the Intergovernmental Panel on Climate Change (IPCC). In his view, the 1.5°C target is dead. Meanwhile, Michael Mann from the University of Pennsylvania in the US and another titan of climate science, spoke for many when he dismissed solar radiation management as “potentially very dangerous” and a “desperate action”. Their positions are irreconcilable. So who is right – Hansen or Mann? Underpinning Hansen’s argument is his conviction that the climate is more sensitive to greenhouse gases than previously reported. The IPCC estimates that doubling atmospheric CO₂ raises Earth’s temperature by 3°C. Hansen calculates it to be 4.8°C. This disagreement isn’t just academic—it fundamentally changes how we approach climate policy. If Hansen’s right, we’re in much deeper trouble than we thought.
The Mystery of 2024’s Unexpected Heat
There is a very intense debate going on among the climate scientist community about whether global warming is accelerating or not due to these really extreme temperatures in the last two years, notes Diana Urge-Vorsatz from the IPCC. Temperatures didn’t return to the “old normal” after the El Niño climate phenomenon ended in May last year like scientists expected they would. Instead, 2024 went on to exceed the 2023 heat record. Some have theorised that a reduction in air pollution may have been reflecting solar radiation and masking the true extent of global warming. On the other side of the debate, scientists see this “blip” as falling within projections for global warming. “A lot of scientists do feel that actually the previous climate models still fully explain this,” Urge-Vorsatz says. We will only know in a few years whether this was just a natural variability blip or it is due to some phenomena that we have not yet understood. It’s like watching a patient’s fever spike unexpectedly—doctors are split on whether it’s a new symptom or just part of the original illness.
Carbon Offset Credibility Under Fire
A study covering almost 300 carbon offset projects found that the industry’s top registries have consistently allowed developers to claim far more climate-saving benefits than justified. Researchers led by Barbara Haya from the University of Berkeley’s Goldman School of Public Policy assessed the methods underpinning forestry projects responsible for 11% of all carbon offsets ever issued. They found shortcomings in each that resulted in bogus credits. “Across the board, they fall far short from good practice in carbon accounting,” Haya said. One study conducted by Sills and collaborators shows that only 6% of the total carbon offsets produced by 18 REDD+ projects across five tropical countries are valid. Most of these renewable-energy offset purchases are not credible, according to Julio Friedmann, chief scientist at consultancy Carbon Direct. “Offsetting is a misnomer — you can’t ‘offset’ your emissions,” she said. “We need alternative ways of supporting climate mitigation because the current offset market is deeply not working.” The disagreement here isn’t subtle—it’s a fundamental challenge to one of the main tools companies use to claim climate progress.
The Net Zero 2050 Reality Check
Current net zero policies will not keep warming to within 1.5°C because they were never intended to. They were and still are driven by a need to protect business as usual, not the climate. Some climate scientists are now openly questioning whether the widely accepted 2050 net-zero target is achievable or even meaningful. We struggle to name any climate scientist who at that time thought the Paris Agreement was feasible. We have since been told by some scientists that the Paris Agreement was “of course important for climate justice but unworkable” and “a complete shock, no one thought limiting to 1.5°C was possible”. Rather than being able to limit warming to 1.5°C, a senior academic involved in the IPCC concluded we were heading beyond 3°C by the end of this century. Gidden and other climate scientists warn that this loose U.N. formula for calculating offsets will fail to halt rising concentrations of greenhouse gases, leading to continuing rising temperatures. These aren’t minor technical disputes—they represent a fundamental crisis of confidence in our current climate strategy.
Failed Experiments and Public Backlash
When Marilyn Ezzy Ashcraft, mayor of Alameda, California, scrolled through The New York Times on a Saturday morning in April 2024, a story about a controversial experiment caught her eye. Researchers from Washington state were trialing a machine that looked like a big snow cannon, which they hoped could one day be used to brighten clouds to reflect more of the Sun’s rays. They’d been spraying tiny salt particles into the air over the San Francisco Bay. At first, Ashcraft wondered which neighboring town was hosting the test. But as she read, she was shocked to learn that the researchers were conducting their experiment right there in Alameda. The story revealed that the researchers had kept the test a secret to limit protests. “It wasn’t just an oversight that they forgot to tell the city,” Ashcraft says. In March 2024, Harvard University shuttered a solar geoengineering research program that would have included the world’s first outdoor stratospheric aerosol injection experiment. The Stratospheric Controlled Perturbation Experiment, or SCoPEx, had planned to launch a weather balloon into the stratosphere over northern Sweden in 2021. Just before launch, the Swedish government canceled the test flight due to resistance from environmental groups and the Indigenous Sámi Council. The pattern is clear: scientists can’t even agree on whether these experiments should happen, let alone what the results mean.
The Politics of Climate Science
Authors of National Climate Assessment Dismissed The Trump administration dismissed all the scientists working on the next National Climate Assessment. The White House has dismissed approximately 400 scientists and other climate experts who were working on a major report about how climate change affects the U.S. On Tuesday, the authors received an email releasing them from their roles, and saying “the scope of the [National Climate Assessment] is currently being reevaluated.” The White House did not respond to questions about why the authors were dismissed or what elements of the report’s scope are being reassessed. This political interference highlights another fracture in the climate science community—not just disagreements about the science itself, but about how science should interact with politics and policy. The 1.5C milestone should serve as “a rude awakening to key political actors to get their act together,” said Chukwumerije Okereke from the University of Bristol. Recent European elections have shifted political priorities towards industrial competitiveness, with some European Union governments seeking to weaken climate policies they say hurt business. Matthew Jones, a climate scientist at the University of East Anglia in Britain, said climate-linked disasters will grow more common “so long as progress on tackling the root causes of climate change remains sluggish”.
The Moral Hazard of False Solutions
There’s the moral hazard argument: that if governments and industries begin to perceive SAI as a reliable plan B for climate change, they’ll use it as an excuse to hold off on making urgently-needed emissions cuts. For many years, all geoengineering research was discouraged by many scientists and experts for fear it would provide an excuse not to cut emissions. Some right-wing politicians such as Newt Gingrich promoted it as a way to reduce global warming without having to cut emissions. Such an approach could also distract people from expanding decarbonization efforts. “Geoengineering doesn’t tackle the root causes of climate change; it’s arranged to counter some of the impacts, but it involves intervening in Earth’s systems at an absolutely enormous scale,” said Mary Church from the Center for International Environmental Law. Scientists are essentially arguing about whether researching these technologies makes the climate crisis worse by providing false hope for easy fixes. It’s a philosophical divide that cuts to the heart of how science should approach existential risks.
The Trust Crisis in Climate Communication
Real and fabricated examples of weather modification have also been fertile ground for mis- and disinformation and conspiracy theories, extending into the geoengineering field. For years, conspiracy theorists have inaccurately alleged that aircraft condensation trails or “chemtrails” are actually signs of weather control, geoengineering, or other nefarious government programs. Research shows high overlap between chemtrails, geoengineering, and other conspiracy theory topics, and conspiracy theorists have threatened scientists in the geoengineering field. Efforts to understand public perception of solar geoengineering have found mixed results. In a 2021 survey of U.S. adults by the nonpartisan Pew Research Center, based in Washington, D.C., about 41 percent of the total respondents — and over 50 percent of Generation Z and millennials — said they think solar geoengineering would mitigate the effects of global climate change. But about 74 percent of the respondents also expressed at least some concern about the consequences of the technology. Climate scientists now find themselves not just disagreeing with each other, but struggling to communicate with a public that’s increasingly skeptical of expert authority. Though research points the way, scientists agree there’s no recipe book for climate-tech engagement that can be used for each new project. But some structural changes would make the process a whole lot easier, social scientists say. “We tend to say, ‘There’s a project here, let’s go and talk to people about what they want,'” says Nawaz.
When Uncertainty Becomes Paralysis
With this July marking the 14th consecutive month to set a global heat record, and 2024 and 2023 likely to be the hottest back-to-back years in history, there is growing concern that global warming and its impacts are escalating far faster than geoengineering policymaking is moving ahead. Regarding SRM benefits, Keith was candid: “Nobody can claim to know what the correct answer is.… It would be much better for the world if people were more [geoengineering] conversations, especially by political leadership.” Keith agreed that an international body needs to set and enforce rules, but he noted that governments are nowhere near to figuring that out. Input from everyone is needed, he added, including UNEP, the National Academy of Sciences, the World Meteorological Society and others. “It’s incredibly depressing that we’re here,” says Shuchi Talati, a climate technology governance expert who founded the nonprofit Alliance for Just Deliberation on Solar Geoengineering in Washington, D.C. “I don’t want to have this conversation. But this is where we are.” The scientific community’s inability to reach consensus is becoming a crisis in itself, as urgent decisions get delayed while the planet continues warming. It’s like a medical team arguing over treatment options while the patient bleeds out on the operating table.
