How confident can we be, even after research and testing, that the chosen technology will work as planned? After all, ocean fertilization — spreading iron slurry across the seas to persuade them to soak up more carbon dioxide — means changing the chemical composition and biological functioning of the oceans. In the process it will interfere with marine ecosystems and affect cloud formation in ways we barely understand.

Enveloping the earth with a layer of sulfate particles would cool the planet by regulating the amount of solar radiation reaching the earth’s surface. One group of scientists is urging its deployment over the melting Arctic now.

Plant life, already trying to adapt to a changing climate, would have to deal with reduced sunlight, the basis of photosynthesis. A solar filter made of sulfate particles may be effective at cooling the globe, but its impact on weather systems, including the Indian monsoon on which a billion people depend for their sustenance, is unclear.

Some of these uncertainties can be reduced by research. Yet if there is one lesson we have learned from ecology, it is that the more closely we look at an ecosystem the more complex it becomes. Now we are contemplating technologies that would attempt to manipulate the grandest and most complex ecosystem of them all — the planet itself. Sulfate aerosol spraying would change not just the temperature but the ozone layer, global rainfall patterns and the biosphere, too.

Spraying sulfate particles, the method most likely to be implemented, is classified as a form of “solar radiation management,” an Orwellian term that some of its advocates have sought to reframe as “climate remediation.”

Yet if the “remedy” were fully deployed to reduce the earth’s temperature, then at least 10 years of global climate observations would be needed to separate out the effects of the solar filter from other causes of climatic variability, according to some scientists.

If after five years of filtered sunlight a disaster occurred — a drought in India and Pakistan, for example, a possible effect in one of the modeling studies — we would not know whether it was caused by global warming, the solar filter or natural variability. And if India suffered from the effects of global dimming while the United States enjoyed more clement weather, it would matter a great deal which country had its hand on the global thermostat.