It's been more than four years since leaders tried and failed to craft a binding new global climate change treaty in Copenhagen, and as nations head toward a new deal in 2015, the aftershocks of that Danish summit continue to reverberate.

From climate campaigners to high-level diplomats, those who are committed to fighting global warming say making a strong agreement in Paris next year that radically reduces levels of greenhouse gas emissions is critical. But, they argue, it's not the last step or perhaps even the most important step in what will be a long battle to avoid catastrophic warming.

That's a turnaround from the thinking that preceded the 2009 Copenhagen summit, which saw the environmental group Greenpeace declare that the deal signed there should be "nothing short of a plan to save the planet." Then-U.K. Prime Minister Gordon Brown wrote a Newsweek article entitled "Copenhagen or Bust." Meanwhile, the United Nations promoted a dramatically ticking Copenhagen countdown clock.

It's a shift, analysts say, that peaked after Copenhagen but in reality has steadily evolved over the past two decades of frustrating climate negotiations.

"If you look at the time since 1992, we sort of started out with a bang, with Rio and Kyoto," said U.N. Foundation Vice Chairman and former State Department Undersecretary for Global Affairs Tim Wirth. The 1992 Rio Earth Summit gave birth to the U.N. climate change regime that five years later created the first-ever climate change treaty, the Kyoto Protocol.

Since then, Wirth said, "Things have slowed down. And you say to yourself, 'Well, why is that?' Because we thought there was going to be a way in which a single formulation was going to work with everybody, and that's proved impossible. We just don't know how to do it. The equity issue is too serious. The 'whodunit' issue is too serious. We just don't know how to handle all those questions on a nation-to-nation basis. So therefore, it seems to me that we have to change course."

A looser agreement that does not echo Kyoto
Any agreement that emerges from Paris next year will, most agree, look fundamentally different from the 1997 Kyoto Protocol. That pact was abandoned by the U.S. Senate because it imposed emissions cuts on wealthy countries but let developing nations -- including China -- off the hook by allowing them to make voluntary cuts in exchange for financial support. President George W. Bush declared Kyoto "dead," and since President Obama entered office, his climate team's top goal has been to avoid the mistakes of Kyoto.

That has meant steadily breaking down what U.S. Special Envoy for Climate Change Todd Stern has called the "firewall" between developed and developing countries. Year after year, starting in Copenhagen, Stern and his team have chipped away at that wall, and what now remains are the outlines of a deal that -- at least on paper -- will see all countries big and small cut carbon.

And yet the deal will also likely be looser. Kyoto was a legally binding agreement that imposed and split up among rich nations a 5.2 percent global emissions cut from 1990 levels. With China now the world's largest emitter and other developing countries booming, there is little appetite left among rich nations to continue in that top-down vein. The United States is leading the charge for a voluntary pact in which countries declare targets that are then enforced with monitoring and reporting efforts.

"Expectations at this stage are much more realistic than they were before Copenhagen, and that's one of the reasons I'm hopeful," said Elliot Diringer, executive vice president of the Center for Climate and Energy Solutions. He noted that the most recent U.N. climate conference in Warsaw last year ended with a decision that countries should announce their "nationally determined contributions" for cutting emissions in the post-2020 era by early next year.

"That's a big hint about the kind of agreement we're likely to see in Paris. The fact that the phrase 'nationally determined' is now in a decision ... reflects the broader discussion about an alternative approach that tries to include top-down and bottom-up," he said.

For Diringer, whose group was among the few trying to put a damper on hopes for a game-changing new climate treaty in 2009, the key lesson from Copenhagen was to avoid "unrealistically high" expectations. Though an advocate of a legally binding treaty, he argued that it is not the most driver of a strong agreement. And, he has cautioned, a deal should not be branded a failure even if the targets included fail to add up to avoiding a 2-degree-Celsius rise over preindustrial levels, as long as it puts countries on a serious path toward achieving that goal that allows for and encourages progressively stronger commitments over time.

Meanwhile, environmentalists who have taken the most heat for raising outsized expectations for Copenhagen are unapologetic. With the future of the planet at stake, they argue, they should only be raising the bar.

"If the numbers don't add up, it's not a political failure only. It's a physical failure," said Wael Hmaidan, director of Climate Action Network (CAN) International. "If you want to get to New York and you only get to New Jersey, you failed, right?"

Many activists recalled the widespread devastation in their ranks after Copenhagen, which they viewed as a failure. Some even hung up their polar bear outfits and called it quits on climate campaigning. But as they bend the corner toward a Paris agreement, Hmaidan rejected the idea that his community needs to manage their expectations.

Not a 'final bite of the apple'
"We just didn't know how to manage the failure. We really did put all our eggs in one basket and we really didn't think beyond Copenhagen," he said. "But trying to avoid failure by reducing expectations is not the way to go. We need to be ambitious and not be afraid to fail. This is what we teach our children."

Ruth Davis, a policy adviser for Greenpeace in the United Kingdom, agreed. Speaking in Warsaw during last year's U.N. climate conference, she said there was an intense level of planning for the two-week December 2009 conference in Copenhagen. But, she said, "not for the morning after."

Now, she said, "We absolutely don't want to get into a situation where we say 'Paris or bust.' But the fact remains that a global treaty is an absolute centerpiece of the kind of action needed to tackle the challenge. The real risk is that people are going to sleepwalk to Paris, that we are going to have a zombie COP. And we're up against time. We will be in a lot of trouble if we get on a pathway from Paris for three or four degrees or higher."

Still, Davis said, even if that happens "We'll get back on the horse the next day."

Jake Schmidt, international climate policy director for the Natural Resources Defense Council, said there has been a developing "sense of maturity" in the climate community since Copenhagen. As of now, he argued, the elements for a strong 2015 agreement in Paris are not yet in place. The United States needs to develop strong new post-2020 targets; the European Union will decide on its 2030 targets later this year; and China needs to move from its current emissions intensity goal to setting a year in which absolute emissions will peak.

"Will they add up? I hope so, but I am not optimistic that this is going to be the final bite of the apple. I don't believe that you pull together these meetings and you're going to solve all the problems in one fell swoop," Schmidt said. But, he argued, the U.N. climate regime is just one of many places climate activists need to invest time and effort to bring about change.

"One reality that has sunk in since Copenhagen is that this is hard, and it's going to require a constant effort at the global level to deal with that challenge," Schmidt said. "It doesn't happen on nuclear nonproliferation, it doesn't happen on trade, it doesn't happen on any environmental multilateral agreement. We cannot delude ourselves that we're going to have one meeting that's going to solve all the world's problems. We can't use just one tool to solve climate change."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500