How about billions of tiny mirrors, launched into orbit to deflect solar rays? Or clouds artificially whitened to reflect more sunlight back into space? Or maybe mechanical trees to suck carbon dioxide from the air along busy highways?
Outlandish as some of these proposals may seem, scientists and engineers are paying increasing attention to such ideas amid mounting evidence that human-caused climate change is already wreaking havoc in some parts of the world. The proposals belong to a field known as geo-engineering, or manipulation of the environment on a grand scale. As a solution to global warming, it remains a highly controversial concept, dismissed as a dangerous distraction by critics or embraced as a quick, if temporary, fix by enthusiasts such as the authors of the best-selling book "Freakonomics."
Regardless, decision-makers are beginning to take notice. At the beginning of the month, the U.S. House Committee on Science and Technology held its first hearing on the topic.
"It's too soon to think about actually doing any of these things, but it's the right time for some serious research and for some funding from the government," said John Shepherd, a professor of Earth science at the University of Southampton in southern England, who testified at the hearing.
Shepherd is a member of the prestigious Royal Society, a fellowship of scientists that released a highly publicized report in September identifying various geo-engineering solutions and assessing their feasibility.
The ideas usually fall into two categories:
A shot in the dark. In one, the goal is to decrease the amount of sunshine hitting and warming Earth. One proposal calls for unfurling a space-based gigantic shade made of a superthin mesh of aluminum threads. A more reasonable alternative, according to the Royal Society, would be to spray sulfate aerosols into clouds to make them brighter, whiter and therefore more reflective.
In general, the "solar radiation management" techniques would offer quick, emergency relief from rising temperatures: a dose of cosmic aspirin to bring down Earth's fever.
A breath of fresh air. The other type of idea calls for removing carbon dioxide from the atmosphere, whether by trapping and storing it via artificial trees or converting it to something else -- for example, tapping the ability of the oceans' algae to convert carbon dioxide into oxygen.
Good ideas: Please ignore them Shepherd, along with virtually all scientists, engineers and other experts in London, stresses that none of these solutions is a substitute for the paramount task of slashing carbon emissions.
That's why, at next month's global summit in Denmark on bringing down greenhouse gas emissions, he hopes that policymakers don't pay too much attention to a talk he's scheduled to give on geo-engineering ideas.
"Geo-engineering is not a magic bullet, and it's not a viable alternative to carbon reduction," Shepherd said. "I hope that this is not going to be any serious component of the discussions in Copenhagen, because it would be premature for any of it to be taken into account."
Many of the ideas are "still at the back-of-the-envelope stage," he said, and the technologies some of them require are years, if not decades, away. For instance, no one knows yet how to catapult 1 million tiny mirrors into space every minute for the next 30 years.
'Pie-in-the-sky'? Or dangerous? Critics worry that too much focus on geo-engineering will divert attention and resources from the immediate need to reduce carbon footprints, or could cause people to become complacent.
"A lot of this is just pie-in-the-sky compared to the clear and obvious things and most cost-effective things that we can be doing straightaway," said Greenpeace's Doug Parr.
In addition to the unproven technologies, he said, there are side effects that could be just as harmful to the environment as climate change. One proposal, pouring iron into the ocean to stimulate the growth of CO2-gobbling algae, would significantly alter the marine ecosystem. Spraying aerosol into clouds would set back the healing of the ozone layer.
This raises questions of ethics and international governance. Who gets to decide which techniques are used and at what cost?
What if it went wrong? "For example, the sulfate aerosols: The consequence of that would almost certainly be to affect rainfall patterns, and when you affect rainfall patterns, there are going to be winners and losers," Parr said. "How do the losers feel about these experiments?"
The aerosol method also comes saddled with the same problem as other sunlight-repelling proposals: the need for constant maintenance and replenishing. Moreover, if anything went wrong or maintenance stopped, all the effects of the pent-up greenhouse gases would come barreling back and Earth would quickly heat up, just as a fever returns when aspirin is taken away.
"The CO2 is still in the atmosphere, and you've got to deal with that," said Nem Vaughan, a researcher at the University of East Anglia in eastern England, which has launched an initiative specifically to study and evaluate geo-engineering.
Many experts prefer the carbon-removal idea, which attacks the source of the disease, not just the symptoms.
Buying the planet some time Tim Fox of the Institution of Mechanical Engineers insists that such measures are feasible. His institution and the Royal Society contend that governments should dedicate a small portion of funding for climate-change research to geo-engineering; at the moment, scientists have been working on such ideas at their universities or "in their spare time," Shepherd said.
Fox emphasizes that geo-engineering proposals form only part of the solution, a way to buy the planet some time while people and nations wrestle their carbon emissions under control, which they so far have not had much success in achieving.
"The reality is we don't have enough time left available to us," he said.
"Rather than get halfway down the track and give up because we're exhausted from the challenge and demoralized from losing the battle, why don't we use all the tools at hand better?"