Harvard University scientists plan to fly a test balloon above Sweden next year to help advance research into dimming sunlight to cool the Earth, alarming environmentalists opposed to solar geoengineering.
Open-air research into spraying tiny, sun-reflecting particles into the stratosphere, to offset global warming, has been stalled for years by controversies - including that it could discourage needed cuts in greenhouse gas emissions.
In a small step, the Swedish Space Corporation agreed this week to help Harvard researchers launch a balloon near the Arctic town of Kiruna next June. It would carry a gondola with 600 kg of scientific equipment 20 km (12 miles) high.
"There are very many real concerns" about the risks of climate change and solar geoengineering, said David Keith, who is involved in the project and is a professor of applied physics at the Harvard School of Engineering and Applied Sciences.