An initiative from Richard Branson, the shaggy-haired billionaire owner of Virgin Atlantic airlines, was emblematic. In February 2007, he offered a cash prize of $25 million to anyone who could come up within just a few years with a process that would suck large amounts of greenhouse gases out of the atmosphere.
Flanked by Al Gore, the former U.S. vice president and the author of the book “An Inconvenient Truth,” Mr. Branson likened his offer to an 18th century competition for a method of estimating longitude accurately that eventually saved thousands of lives at seas.
“Man created the problem, therefore man should solve the problem,” said Mr. Branson, who was referring to global warming. His initiative to help ensure the stability of the climate was “the largest ever science and technology prize to be offered in history,” Mr. Branson said.
Nearly four years later, Mr. Branson’s plans to award that prize, known as the Virgin Earth Challenge, are effectively on hold.
One problem is that some of the most promising ideas among the approximately 2,500 applications submitted for the award proposed projects raising tricky environmental and social issues.
Many of applicants suggested ways of manipulating the climate, which also is known as geo-engineering, and which relies on processes like releasing sulfur particles at high altitude to produce a haze blocking the sun’s rays, or using the oceans to absorb more carbon dioxide.
Mr. Branson now recognizes that there is “a level of unease that’s out there, based on impacting the atmosphere,” said Nick Fox, a spokesman.
Another problem is that none of projects is anywhere near ready to for deployment at a scale needed to capture significant amounts of planet-warming gases.
Among the applicants were “very eminent scientists” as well as people doing “a lot of garage-type projects.” But none was “developed enough to be commercialized right now,” Mr. Fox said.
The delay in awarding the prize illustrates how even the most generous incentives for finding ways of capturing gases linked to global warming may prove ineffective.
Projects for a technology called carbon capture and sequestration — which are ineligible for Mr. Branson’s prize because they aim to capture gases from gas and coal power plants before they are released into the atmosphere — have also fallen behind schedule.
To be sure, part of the reason for those delays is that government budgets have been ravaged by the worst global economic slowdown in generations. Demand for electricity has dipped further, weakening the incentives for utilities to fund new coal and gas power plants with the new equipment.
But another reason for the delays is the mounting concern among residents living near potential carbon dioxide repositories, suggesting that public acceptance could become a major hurdle for these projects.
In the United States in September, a Native American council canceled its earlier approval of a project because of concerns about environmental damage, groundwater contamination and public safety.
This month, the Dutch government canceled a project with the oil and gas company Royal Dutch Shell to bury carbon dioxide below the town of Barendrecht, after residents and local officials opposed the plan.
Critics also say that such projects divert funds from initiatives to get people to conserve energy and develop renewable sources that do not rely on burning fossil fuels in the first place.
Even so, the European Union has agreed to spend as much as €5.5 billion, or $7.5 billion, constructing as many as a dozen demonstration plants by 2015, partly because fossil fuels like coal will remain the world’s principal source of energy in coming decades, said Eric Drosin, a spokesman for the Zero Emissions Platform, a group of companies, researchers and environmental associations that advises European authorities on carbon capture and storage.
Mr. Drosin said that the E.U. commitment showed the technology was viable.
Mr. Branson has emphasized that trapping carbon dioxide would give the planet an insurance policy against ever-rising levels of emissions. He also has brushed away accusations of hypocrisy based on his intention to keep running a major airline. He has said that if he grounded his fleet, another company would step in to meet the inevitable consumer and business demand.
Mr. Fox, his spokesman, said that by sometime next year, experts at the Virgin Earth Challenge should have whittled the 2,500 applications from the initial round, which closed at the start of this year, down to a list of six or seven projects.
Mr. Branson has already made clear his doubts about some of the applicants.
“Changing the chemistry of the oceans to promote plankton growth however feels very risky, seeding clouds likewise,” Mr. Branson wrote on the Virgin Earth Challenge Web site. More promising projects included initiatives related to biochar, or trapping carbon dioxide in charcoal form, Mr. Branson suggested.
Under the rules of the competition, any winner would need to provide a “commercially viable design” for removing at least one billion tons of atmospheric carbon dioxide per year for 10 years.
That still is unlikely by next year. So rather than awarding the prize money to one or more of the shortlisted projects immediately, Mr. Branson probably will propose an interim strategy, funded in part by the Virgin Group and perhaps other private financiers, to support the work further.
“We need an in-between stage to attract industrial and energy partners for these projects,” Mr. Fox said. “Awarding one of these projects $25 million now won’t do the planet much good when what we’ve actually learned these past years is that it still might take as much as $2.5 billion to develop a machine or process to suck the carbon out of the air, and keep it out,” he said.