Some weird science is getting serious looks by leading climate experts who say it would be folly not to prepare emergency measures to try to stop global warming in its tracks. This is going on despite the well known risk of unintended consequences whenever humans meddle with nature.
The scientists' worry is that global temperatures are now rising steadily and the process may get beyond any hope of being stopped by cutting greenhouse gas emissions alone.
"These 'geo-engineering' ideas are something any serious scientist approaches with extreme caution," NASA earth studies expert James Hansen told ABC News.
"But we're at the hairy edge," he said. "We 've only got about 10 years to turn the carbon emissions around, and so you're finding more scientists thinking about these things."
Some astonishing ideas are popping up -- like a monster sunshade for planet Earth.
NASA has asked University of Arizona professor Roger Angel to flesh out his idea for a gigantic sunshade in space.
For only $3 trillion, says Angel, a "solar shield" could be made of mirrors that would span 1,200 miles of space, 950,000 miles away from the earth, to block some of the sun, making the earth cooler.
Angel argues that while $3 trillion may sound like a lot, it's less than 2 percent of the world's gross national product.
But what if the mirrors' tilt controls fail? Could mankind really build the necessary space vehicles needed to repair something so huge in time? And if runaway warming starts, would there even be enough time to build such a massive structure anyway? There are no clear answers.
Some scientists suggest turning the earth's blue skies a yellowish grey by injecting sulphur dioxide into the atmosphere with a vast fleet of planes.
The sulphur dioxide would reflect warming sunlight back into space.
But the psychological effect on humanity of a world without blue skies -- to say nothing of the effect on earth's plants and animals -- is clearly incalculable.
And what would all that sulphur dioxide do to the oceans into which it would soon settle?
Even though that part hasn't been worked out yet, climate scientist Tom Wigley of the National Center for Atmospheric Research is promoting the sulphur skies idea in the premier research journal Science.
A number of scientists have suggested blanketing enormous sections of the planet 's deserts with plastic sheets to reflect sunlight straight back into space, preventing it from warming the earth.
That might work because sunlight, coming in or reflected back out to space, passes right through greenhouse gasses -- unlike the infrared heat a warmed earth gives off, which gets trapped in those gasses.
But scientists admit they're not sure how to maintain such immense reflectivity: would a few good dust storms -- already increasingly common on our warming planet -- dull the giant reflective sheets, requiring a huge cleaning staff ? How many vacuum cleaners would they need?
Another idea being seriously debated among scientists is to send a fleet of ships into the world's oceans to sow the waves with iron particles.
The iron would stimulate massive growth of the sea's myriad tiny plankton, which flourish on a diet of iron.
The plankton, which also love carbon dioxide, would then suck up huge chunks of it -- the same CO2 which causes global warming.