As the Copenhagen climate conference dominates headlines this week, it's easy to forget that just a few years ago such summits went largely unnoticed by the public.
That's because even though global warming was widely discussed, there was little public sense it was an urgent problem.
Now that has changed dramatically, and the Copenhagen conference is providing ample proof of the extent.
The two-week conference has drawn some 15,000 people, and only a few hundred of them are actually delegates from the 192 participating countries.
The rest are scientists, representatives of NGOs, members of interest groups, and even simply onlookers. There are so many people, in fact, that Demark has deployed half of its police force to Copenhagen just to assure order.
What happened to make Copenhagen such a huge, global happening?
One change is a growing sense that countries are united in their desire to tackle global warming by controlling greenhouse emissions.
"The time for formal statements is over," UN climate chief Yvo de Boer said at the opening of the summit on December 7. "The time for restating well-known positions is past. The time has come to reach out to each other."
Part of the optimism comes from the active role now being played in the conference by the world's two biggest carbon emitters, China and the United States. Both have promised to control or cut emissions.
By contrast, neither country ratified the emissions-cutting treaty that came out of the last great global warming conference in Kyoto in 1997.
But a still more important reason for intense interest in Copenhagen may be a shift in public opinion that began as recently as seven years ago.
Pushed To The Fore
It was only in 2002 that the U.S. government acknowledged for the first time that man-made pollution is largely to blame for global warming.
Then there were the Nobel Peace Prize awards of 2007.
The prize went partly to the UN Intergovernmental Panel on Climate Change (IPCC), which warned greenhouse gas emissions could lead to extreme climate patterns including floods, droughts, and storms.
It also went to U.S. Vice President Al Gore, whose "An Inconvenient Truth" placed the connection between human activities and global warming on theater screens around the world.
But if many people now regard global warming as an urgent, and potentially catastrophic problem, the world is still a long way from finding a solution.
Potential strategies for curbing global emissions involve hundreds of billions of dollars, with developed countries helping to fund the efforts of developing ones. That is giving rise to new debate of whether the cost may be too much to bear, even as Copenhagen goes forward.
"I think that there's a lot of reason to hope, but I still think that because of this horrible recession the world's been in, the big obstacles at Copenhagen are going to be economic ones," former U.S. President Bill Clinton told reporters in New York as the conference opened.
That may mean that even though the summit has started with calls for unity, any agreements could yet prove highly divisive.
Just how divisive can be measured by one debate that got much press attention in the run-up to the summit. The question was whether the scientific evidence of global warming is strong enough to justify massive new government spending programs.
The argument was fueled by what the press has called "Climategate"-- an illicit peek into the private e-mails of scientists at a leading British climate research center, the University of East Anglia.
Critics of the Copenhagen process say the e-mails, anonymously purloined and posted on the Internet, provide evidence that the researchers conspired to exaggerate the threat of global warming.
Climategate led to the resignation of the director of the research center. There were also calls for investigations, including in the U.S. Congress, which has yet to agree on U.S. emissions-reduction targets after months of discussion.
Those who say climate change is urgent argue that, with or without Climategate, there is enough evidence from multiple scientific groups to make the case for action.
Still, the dispute shows the extent of the passions the global warming issue raises and what kind of battles may lie ahead.
Not So Fast
Benny Peiser, director of The Global Warming Policy Foundation, says governments are rushing the public into expensive emissions-curbing programs with little public support.
"Obviously in the middle of an economic crisis, people have other priorities," Peiser says. "They are concerned about jobs and they are increasingly concerned about the cost implications of very unpopular taxes, green taxes, climate taxes, emissions-trading schemes, cap and trade, all of this comes with a hefty price tag and people are very concerned about this."
He argues more time is needed for scientists to study the problem and prove such emission cuts would solve it.
But others call, just as pressingly, for immediate emission curbs and say the science is already proven.
"We need a carbon levy to finance the global public good of adaptation and mitigation of global climate change," Jeffrey Sachs, an economist at Columbia University. "And the United States, as the world's largest carbon emitter per capita of any major economy, should be called on first to make good on this promise."
How much such debates over new taxes will dominate headlines in coming months will depend greatly on the urgency and type of emission cuts agreement to come out of Copenhagen.
The world leaders who attend the closing days of the conference next week will help to shape the agreement.
But the agreement itself must go to the legislatures of each home country to be ratified. And if the arguments already going on around Copenhagen are any guide, that will not be an easy process.