This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: No, President Joe Biden did not engineer Hurricane Milton. No, the ice crystal contrails left behind by high-altitude aircraft are not "chemtrails" sprayed by governments to control the weather or manipulate populations.
No, state-run cloud seeding did not cause the record floods in Dubai. Yet claims like these are widespread online and increasingly find their way into political rhetoric. This blurs the distinction between conspiracy theories about weather manipulation and the very real scientific debate over solar geoengineering.
Solar geoengineering, also known as solar radiation modification (SRM), would try to temporarily cool the climate by altering the amount of energy entering or leaving the Earth system. Outdoor field experiments are particularly contentious, with researchers and other experts divided over whether they should proceed at all and, if so, under what conditions. The best-known proposal, stratospheric aerosol injection, involves dispersing sulfur dioxide high in the atmosphere, where it can form reflective particles known as aerosols.
These can remain in the stratosphere for long periods, broadly mimicking the cooling effect of major volcanic eruptions. The other main proposals are marine cloud brightening, which would add sea-salt particles to low clouds over the sea to make them more reflective, and cirrus cloud thinning, which would aim to reduce the net warming effect of high-altitude clouds. In our recent study, colleagues and I examined what outdoor SRM experiments might look like in practice.
We identified plausible experiments across the three approaches and examined how their scientific purpose and regulatory requirements change with scale. The paper is published in the journal Earth's Future. Rather than a simple "small" or "large" distinction, we found discrete phases with increasingly stringent regulatory scrutiny at each stage—think of it like a steep staircase as scale increases.
I focus here on stratospheric aerosol injection, the most extensively studied proposal, as it best illustrates the gulf between experimentation and deployment. Recent simulations suggest that around 8 to 16 million tonnes of sulfur dioxide would need to be injected each year to produce 1°C of cooling. An interactive simulator lets you experiment with these numbers yourself.
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