– A team of elder Silicon Valley scientists is building an audacious device that might solve one of humanity’s most profound dilemmas — a “cloud whitener” designed to cool a warming planet.

The men — retired physicists, engineers, chemists and computer experts from some of Silicon Valley’s top tech companies — have been meeting four days a week for seven years in the Sunnyvale lab of the Marine Cloud Brightening Project to design a tool that creates perfectly suspended droplets of water resembling fog.

Their goal is to launch the nation’s first open-air field trial of “geoengineering” in Moss Landing. There, they would test the ability of an energy-efficient machine to hurl tiny seawater droplets into a graceful trajectory — the first step of a research project to boost the brightness of clouds to reflect rays of sunlight back into space.

“We are interested in an insurance policy for global warming,” said Jack Foster, 79, a physicist and laser pioneer. “We are not interested in deploying it unless it’s necessary. But we’d like to have something available.”

The effort to conduct even a small-scale test — overseen by the University of Washington, which has numerous experts in atmospheric science — represents a dramatic shift in thinking in the scientific community, which until recently resisted conversations about deliberate manipulation of the climate.

The reason for the change: There is scientific consensus that even if the world succeeds in shifting away from fossil fuels, warming of the planet is inevitable — and it may have catastrophic consequences.

Critics of geoengineering, however, warn against altering nature’s patterns, arguing that we don’t yet understand all the potential ramifications. And they worry that if people see a quick fix for climate change, they may not try as hard to reduce greenhouse gas emissions.

“Personally, I doubt that the world is ready for this,” said Stephen Gardiner, a University of Washington philosophy professor. “Geoengineering raises huge ethical and political questions, nationally and internationally.”

But the Silicon Valley scientists say the world might not have a choice. “We need to research the technology,” said project leader Armand Neukermans, 74, whose achievements include the development of the earliest ink jet printers and who led teams at Xerox Labs, Hewlett-Packard, Tencor and Xros.

None of the men will be alive by the end of this century, when the concentration of carbon dioxide in the atmosphere is expected to be double what it is now — and temperatures are likely to be so high they will harm ecosystems and human health and welfare. “But all of us have children or grandchildren,” Neukermans said. “We’ve got to preserve the future.”