Researchers are divided over what experiments involving solar geoengineering can reveal—and whether such experiments should even take place. Online, claims range from the outlandish, such as the idea that President Joe Biden engineered Hurricane Milton, to more grounded but still controversial theories, such as that aircraft contrails are "chemtrails" used for weather control or that cloud-seeding caused floods in Dubai. These ideas blur the line between conspiracy theories and the real scientific discussions about solar geoengineering, a proposed method of cooling the planet. Solar geoengineering, also known as solar radiation modification (SRM), aims to temporarily cool the climate by altering how much energy enters or leaves the Earth system. Among the most contentious aspects of SRM are outdoor field experiments, which many experts debate should proceed at all and, if so, under what conditions. One of the most well-known SRM proposals is stratospheric aerosol injection, which involves dispersing sulfur dioxide high in the atmosphere. There, it would form reflective particles known as aerosols, mimicking the cooling effect of major volcanic eruptions. Other proposals include brightening marine clouds and thinning high-altitude cirrus clouds to reduce warming. In a recent study, I and colleagues explored what outdoor SRM experiments might look like in practice. We identified plausible experiments across different SRM approaches and examined how their scientific goals and regulatory requirements change with scale. Rather than a simple "small" or "large" distinction, we found that the process involves discrete phases with increasingly strict regulatory scrutiny. Focusing on stratospheric aerosol injection, which is the most studied, helps highlight the gap between experimentation and actual deployment. Recent simulations suggest that injecting around 8 to 16 million tonnes of sulfur dioxide annually would be needed to produce 1 degree Celsius of cooling. However, proposed outdoor research could start with much smaller releases. Our study identified a range of increasingly large trials, each with specific scientific goals. Smaller experiments could examine how aerosols form or how different particles behave in the stratosphere. Larger trials, involving thousands of tonnes of sulfur dioxide, could track how an aerosol plume evolves under different atmospheric conditions, helping to test models of how particles spread and affect sunlight. At the largest scale we considered—about 1,000 tonnes of sulfur dioxide—the resulting aerosol plume would be comparable in size to the 3D grid cells used in climate models. This could allow computer predictions to be directly compared with experimental observations. A Boeing 777 flight emits about 80–100 kilograms of sulfur dioxide, while 1,000 tonnes is similar to the annual emissions of a mid-sized U.S. coal-fired power plant. However, these comparisons are about quantity, not environmental impact. A coal plant emits sulfur dioxide closer to the ground, along with greenhouse gases like CO₂. These comparisons help clarify the physical scale of proposed experiments. Critics argue that even small-scale research could lead to momentum toward larger trials and eventually deployment. They fear that each experiment might normalize the next, building infrastructure and scientific communities that make it harder to stop. Some call for a complete ban on public funding, outdoor experiments, patents, and dedicated research programs. A recent paper suggests that some opposition to SRM cannot be resolved by scientific evidence alone. For parts of the environmental movement, concerns go beyond technical feasibility, focusing on the social and political systems that SRM might support—such as continued reliance on existing economic structures and less pressure for systemic change. Decisions about SRM must weigh the risks of intervention against the risks of continued global warming, including whether governments could reliably manage a long-term intervention. One analogy is that SRM could function "like a tourniquet"—not a cure, but a way to reduce harm while more permanent solutions are developed. Rapid emissions reductions and carbon removal remain central to tackling climate change, while SRM research explores whether temporary cooling could reduce acute climate risks as those measures scale up. Current policy reflects this balance. European scientific advice recommends a moratorium on using SRM while continuing research under strict ethical conditions. The Convention on Biological Diversity also allows for small-scale research under specific conditions. However, there is no clear boundary between "small-scale" research and deployment. Clearer definitions would make evaluating each experiment more straightforward. Ultimately, while SRM may never be deployed, decisions about specific experiments should be based on what they aim to achieve. Public debate, though not requiring agreement, is essential to address these complex issues.