In the end, it may not have been the pronouncements of scientists and policymakers that ultimately proved convincing, but something more tangible and immediate: the weird weather.
In The News
The topic of climate change was never far from the headlines in 2006.
In January, the U.S. government agency that runs the National Weather Service announced that nine of the 10 warmest years on record have occurred since 1995.
In February, experts on Greenland glaciers reported that the frozen rivers are melting, dumping twice as much ice into the Atlantic Ocean than they did a decade ago.
In May, a documentary on the dangers of climate change, "An Inconvenient Truth," premiered. Starring former U.S. Vice President Al Gore, the film has become the third highest-grossing documentary of all time in the United States, and has reportedly boosted Gore's political prospects in the 2008 presidential race.
In October, former World Bank chief economist Nicholas Stern released a study commissioned by the British government that warns that failure to avert the consequences of global warming could risk a worldwide recession costing up to 20 percent of global GDP.
Apparently more persuasive than reports, movies, or scientific conferences, however, was the weather itself.
The Public Takes Notice
"The general public got engaged in this issue over the last year or two in a manner that it had not been before, simply because the effects of climate change -- at least in terms of things happening out there in the climate that were clearly examples of what we could see in the future, such as more intense hurricanes and killer heat waves -- all became more obvious," says Michael Oppenheimer, professor of geosciences and international relations at Princeton University.
Oppenheimer is referring to record heat waves last summer in parts of the United States and Europe. For example, July was the warmest month since official measurements began in the Netherlands, Belgium, Germany, Ireland, and Britain. A similar heat wave baked Europe in the summer of 2003.
Oppenheimer is careful to point out that these hot summers may or may not be directly related to global warming. They could simply be anomalies in our normal weather patterns. But either way, he says, they give people a worrisome preview of the type of changes global warming could bring.
Michael Mann, director of the Earth System Science Center at Pennsylvania State University, agrees. He says most climatologists are reluctant to blame any particular weather event on human-induced climate change.
A Frog In A Pot
Nonetheless, Mann says, the unusual weather patterns have had "resonance" with the public.
"What people perceive on a day-to-day basis really has a strong influence on how they perceive this problem," Mann says. "Climate change is this slow, gradual change in the climate, and people [behave] much like a frog who is put in warm water that is slowly turned up and doesn't jump out in time before it gets too hot. I think there is this same problem with human society."
Like the frog, Mann believes, the public has been slow to react to climate change, slow to reach the same consensus that much of the scientific community already has.
In fact, Mann thinks that humans and their carbon-dioxide emissions have already guaranteed there will be a certain amount of future global climate change -- regardless of what happens with carbon emissions in the future.
"Now we believe that we have probably already put enough increased greenhouse-gas concentrations into the atmosphere to sort of lock in several more decades of climate change, several more decades of global warming, several more decades -- in fact, at least a century or more -- of increases in sea level," he says.
James Hansen, director of NASA's Goddard Institute for Space Studies in New York, announced in November that he believes the world has less than a decade to take decisive action to prevent irreversible damage, damage that could cause catastrophic changes.
The speed with which global warming trends might lead to catastrophic environmental changes is hotly disputed.
The chief science adviser to the U.S. government, John Marburger, says "we know things like [abrupt climate changes] are possible, but we don't have enough information to quantify the level of risk."
Driving the sense of urgency among some scientists is the fact that climate changes can be observed taking place much more quickly today than had been predicted.
"Some of us believe that we are seeing now a change that the [scientific] models told us should not happen for another 50 years," Mann says. "The Greenland ice sheet -- the models generally have told us that the melting process would be relatively slow and really wouldn't be noticeable until decades from now."
Scientists predict that if the Greenland ice sheet were to melt, sea levels would rise by about 5-6 meters globally, inundating several of the world's largest cities. In 2005, 225 billion cubic meters of Greenland ice melted, compared to 92 billion cubic meters in 1996.
As with almost any kind of change, richer countries will be less vulnerable than their poorer counterparts. And countries with large areas of territory in the far north will likely be better off than the low-lying countries in the Southern Hemisphere.
Big Losers, Little Losers
But the unpredictable nature of climate change, according to Oppenheimer, means that climate change will not create winners and losers -- just "big losers and smaller losers."
"What we really have to worry about are the things that we can't predict," he says. "We're talking about the whole Earth system here. It's not like you can pluck out Canada or Russia in isolation. They live in a world, and if things are falling apart for the rest of the world, it's not going to help them."
And if an environmental disaster hits one country, then the consequences may be quickly felt in the surrounding region, through the movement of refugees, for example.
Oppenheimer says experts are predicting that global climate change could someday create tens of millions of "environmental refugees."
View a photo gallery summarizing some key findings of the Stern report on the economic costs of global warming (epa)
THE STERN REPORT: In October, former World Bank chief economist Sir Nicholas Stern issued a 700-page report on the economic impact of global warming. The report, which was commissioned by the British government, estimates that climate change could cost between 5 and 20 percent of global GDP by the end of the century....(more)