BOULDER, Colo. – Turns out climate policy has some tipping points.

Failure to set and meet strict targets for greenhouse gas emissions cuts over the next 40 years could put long-term goals – such as limiting planetary warming to 2ºC by 2100 – permanently out of reach.

That's the conclusion of one of the first analyses to explore the relationships among energy use, mid-century targets and long-term policy options, published Monday by the Proceedings of the National Academy of Sciences.

The study establishes the notion of "feasibility frontiers," the point at which end-of-century goals become unobtainable or increasingly unlikely unless specific mid-century benchmarks are met.

The study also for the first time establishes odds of hitting specific long-term targets. If energy demand remains high, for instance, it finds that even if the world's governments manage to cut global emissions in half by 2050 and then do everything possible to limit emissions from 2050 on, society has only even odds of limiting global temperature increases to 2º, a goal noted in the recent Copenhagen Accord.

These so-called "mid-century" benchmarks must be hit, in other words, to preserve options for future generations. The study was published by scientists from the National Center for Atmospheric Research in Boulder, the International Institute for Applied Systems Analysis in Austria, and the Energy Research Center in the Netherlands.

"The long-term target discussion, as important as it is, is less important than the interim," said Michael Oppenheimer, a climate scientist and policy expert at Princeton University who was not involved in the study but is familiar with the research.

Another example of a long-term goal is a cap on atmospheric carbon dioxide concentrations, which today are rising as a result of human activity. The science is not clear what level poses a threat, but some research suggests concentrations must remain at or below 450 parts-per-million to prevent drastic climate change. Some advocacy groups seek a goal of 350 ppm, a level the atmosphere surpassed during the Reagan administration. Preindustrial levels were 287 ppm; today's readings are closer to 387.

But emissions today are on a path toward 550 ppm or beyond. If a 50 percent emissions cut is deemed too expensive for today's economies, and emissions instead remain flat for the next few decades – no easy feat in itself – the chances of holding atmospheric carbon dioxide concentrations at 480 parts per million or less evaporate. Even a future with 550 ppm CO2 becomes – depending on various energy assumptions – difficult or extraordinarily expensive to achieve, according to the analysis.

"There's a cost to preserving options," said NCAR climate scientist and lead author Brian O'Neill. "What is the value of preserving an option you may want to exercise in the future?"

Gary Yohe, an economist at Wesleyan University, said the paper is notable for showing that climate policy has tipping points that work much the same way such thresholds work in various Earth systems. Tip an ecosystem or planetary process – such as the atmospheren – too far in one direction, and it may suddenly and irreversibly "flip" into an altered state that precludes any notion of going back to the unaltered version.

These feasibility frontiers work similarly. Fail to make specific targets by mid-century, O'Neill said, and no amount of effort will bring long-term goals in range.

The authors preclude any pie-in-the-sky solutions such as radical behavioral change or unproven technologies such as geo-engineering and nuclear fusion.

Other scientists call the work groundbreaking for the urgency it lends to a task that has so far eluded the world's leaders: translating long-term goals into short-term action.

The discussion about near-term targets, Oppenheimer said, is the next step in both climate modeling and policy. "The policy decision has always been one step behind the reality, and what Brian's doing is really looking over the horizon."

As more countries focus on the next few decades, Oppenheimer said the task, oddly enough, becomes easier. "A lot becomes possible. The world opens up in terms of where we need to go, how ambitious we can be, how ambitious we need to be," he said. "You want to send policy makers a message that their emissions decisions really need to fit within a certain box.

"This is the next step in a longer discussion."

And it puts the cost of failure in plain language, added Yohe, who was not author of the study but is familiar with the research.

"There are thresholds here as well," he said. "You might find yourself running into a wall where you thought there was a door."

"These guys have said if you wait too long, or if you don't do 'x,' the cost of even trying to achieve 'y' is just going to go through the roof," he added.

"That's a currency that everybody talks about."

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.