As the months passed in 2069, Vietnam found some relief thanks to the solar geoengineering project. But things eventually take a turn. With the South China Sea lapping inland along more than 2,025 miles of shoreline, Ho Chi Minh City and Hanoi grow ever-more crowded and smog-choked as hungry farmers give up on betting against increasingly unpredictable growing seasons and flee to find work in metropoles.

The solar geoengineering, while staving off heat waves in Paris and New York, contributes to a drought in the Mekong Delta. The sulfur aerosols that calm storms in the northern Atlantic strengthen one of the dozens of typhoons that hit Vietnam each year and claim many lives.

Geoengineering is revealed as a political force. The most powerful nations — those with the resources to develop and deploy the technology — exert their will through the sun-reflecting spray, directly affecting life in smaller countries. In response, perhaps the people of Vietnam — the sliver of a country that managed to expel the French and American empires and repel the Chinese in roughly two decades during the 20th century — push back, sparking a new conflict. Or maybe they don’t, and a new world order emerges that is defined by those who shape the climate.

The hypotheticals, far off as they may seem, merit examination, especially as some now call geoengineering “inevitable.”

There are few international rules governing geoengineering.

“There’s questions about how precisely we could do it, whether there would be disagreements, what the risk of termination shock would be, whether it would undermine emissions cuts,” said Jesse Reynolds, a geoengineering researcher at the University of California, Los Angeles. “Whether it’s technically possible has never been a question.”

In October, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) determined that world governments must halve emissions by 2030 to keep the planet from warming 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels. Beyond that average temperature, the droughts, storms, and sea-level rise wrought by climate change are expected to be cataclysmic, causing up to $54 trillion in damages and diminishing food and water resources that — even without global warming — would face stress from a ballooning global population.

Even with ambitious efforts to reduce emissions, extra action will be necessary, the IPCC found. The report suggested that “negative emissions technologies” were needed to suck greenhouse gases out of the air. The authors emphasized at a press conference that the first and most reliable “technology” to absorb emissions is trees. But solar geoengineering is emerging from the fringes of the broader climate policy debate.

The journalist Kate Aronoff documented the nascent push in a recent In These Times feature. The governments of the United Kingdom and United States have sponsored research into geoengineering over the past few years, and influential outlets, including the New Yorker and the New York Times, have published articles on it, as Aronoff wrote. An editor at the Economist wrote a book on the subject, called The Planet Remade. Geoengineering even found an Ivy League home base at Harvard University.

Despite the swelling interest in the subject, there are few international rules governing geoengineering. In 2010, the United Nations declared a moratorium on geoengineering under the guise of its Convention on Biological Diversity, citing the unknown effects that “technofixes” for climate change could have on wildlife.

The convention’s mandate is buttressed by another 1977 convention, which states that “the term ‘environmental modification technique’ refers to any technique for changing — through the deliberate manipulation of natural processes — the dynamics, composition or structure of the Earth, including its biota, lithosphere, hydrosphere and atmosphere, or of outer space.” But it goes on to say that “the provisions of this Convention shall not hinder the use of environmental modification techniques for peaceful purposes.”

Short of worldwide consensus about how the technology should be used and who should control it — and remember now that nations can barely agree on an acceptable path toward curbing their own emissions — geoengineering would be controlled by a great power like the United States, China, or Russia. One or more of these world powers would carry out the project and enforce the rules, propelling us into a new era of climate imperialism where the very fundamentals of life in smaller nations — how much it rains, how much sunlight plants can absorb — are directly affected by the actions of a hegemon.

The risks have left climate scientists “sharply divided over geoengineering, in much the same way that Manhattan Project scientists were divided over nuclear weapons after World War II,” wrote Clive Hamilton, an Australian public ethics researcher, in the Bulletin of Atomic Scientists in 2013. “Testing a geoengineering scheme, such as sulfate aerosol spraying, is inherently difficult,” he wrote. “Deployment would make political decision makers highly dependent on a technocratic elite. In a geoengineered world, experts would control the conditions of daily life, and it is unlikely that such a regime would be a just one.”

That hasn’t stopped countries, namely China, from experimenting with small-scale geoengineering schemes already. Faced with declining snowfall in the Tibetan Plateau, a major source of water for Asia, the Chinese government began deploying an array of silver iodide furnaces to “seed” clouds over the region last year. The furnaces burn chemical fuel to produce a special smoke that mixes with clouds, setting off a chain reaction that causes precipitation. The plan has been called the “largest-ever weather modification project.”