Scientists are sucking carbon dioxide from the air with giant fans and preparing to release chemicals from a balloon to dim the sun's rays as part of a climate engineering push to cool the planet.
Backers say the risky, often expensive projects are urgently needed to find ways of meeting the goals of the Paris climate deal to curb global warming that researchers blame for causing more heatwaves, downpours and rising sea levels.
The United Nations says the targets are way off track and will not be met simply by reducing emissions for example from factories or cars - particularly after US President Donald Trump's decision to pull out of the 2015 pact.
They are pushing for other ways to keep temperatures down.
In the countryside near Zurich, Swiss company Climeworks began to suck greenhouse gases from thin air in May with giant fans and filters in a $23 million project that it calls the world's first "commercial carbon dioxide capture plant".
Worldwide, "direct air capture" research by a handful of companies such as Climeworks has gained tens of millions of dollars in recent years from sources including governments, Microsoft founder Bill Gates and the European Space Agency.
If buried underground, vast amounts of greenhouse gases extracted from the air would help reduce global temperatures, a radical step beyond cuts in emissions that are the main focus of the Paris Agreement.
Climeworks reckons it now costs about $600 to extract a tonne of carbon dioxide from the air and the plant's full capacity due by the end of 2017 is only 900 tonnes a year. That's equivalent to the annual emissions of only 45 Americans.
And Climeworks sells the gas, at a loss, to nearby greenhouses as a fertiliser to grow tomatoes and cucumbers and has a partnership with carmaker Audi, which hopes to use carbon in greener fuels.
Jan Wurzbacher, director and founder of Climeworks, says the company has planet-altering ambitions by cutting costs to about $100 a tonne and capturing one percent of global man-made carbon emissions a year by 2025.
"Since the Paris Agreement, the business substantially changed," he said, with a shift in investor and shareholder interest away from industrial uses of carbon to curbing climate change.
Isolating carbon dioxide is complex because the gas makes up just 0.04% of the air. Pure carbon dioxide delivered by trucks, for use in greenhouses or to make drinks fizzy, costs up to about $300 a tonne in Switzerland.
Among new university research, a Harvard geo-engineering project into dimming sunlight to cool the planet set up in 2016 has raised $7.5 million from private donors. It plans a first outdoor experiment in 2018 above Arizona.
Some research has suggested that geo-engineering with sun-dimming chemicals, for instance, could affect global weather patterns and disrupt vital Monsoons.
And many experts fear that pinning hopes on any technology to fix climate change is a distraction from cuts in emissions blamed for heating the planet.
But governments face a dilemma. Average surface temperatures are already about 1°C above pre-industrial levels and hit record highs last year.
"We're in trouble," said Janos Pasztor, head of the new Carnegie Climate Geoengineering Governance Project. "The question is not whether or not there will be an overshoot but by how many degrees and for how many decades."
The most natural way to extract carbon from the air is to plant forests that absorb the gas as they grow, but that would divert vast tracts of land from farming. Another option is to build power plants that burn wood and bury the carbon dioxide released.
Among other possible geo-engineering techniques are to create clouds that reflect sunlight back into space, perhaps by using a mist of sea spray.