The word is "ambition," and it's being voiced this summer with extra urgency by those who worry that the world's leaders won't soon commit themselves to measures strong enough to combat climate change.
In September, heads of state are to gather at a United Nations climate summit to cheer each other on. In December in Peru negotiators are supposed to produce a draft treaty binding the world to decades of steep cuts in greenhouse gas emissions. And early next year each country is expected to spell out just how deeply it will cut its own global warming pollution. The hope is to have a deal done in Paris by the end of 2015.
It's a daunting timetable. But the way to keep on pace, experts warn, is not to lighten the load.
"The key challenge," as two Brookings Institution scholars recently summed it up, is "generating enough ambition among the major greenhouse gas emitters that collectively their actions...will put the world on a pathway" to keep warming within the 2 degrees Celsius safe limit.
Here are three recent treatments of the ambition question. One looks at just how much countries might ask of themselves; one examines how a classic economic model might be made more pertinent to the climate threat; and one measures recent actions by the Obama administration against a high standard of ambition.
Teams of independent experts from 15 countries have spent months considering how deeply each nation might reduce their emissions if their leaders are ambitious enough.
The report is a joint project of 30 participating scientific institutions. The countries include Australia, Brazil, Canada, China, France, Germany, India, Indonesia, Japan, Mexico, Russia, South Africa, South Korea, the United Kingdom and the United States. The project was sponsored by the Sustainable Development Solutions Network at Columbia University and the Institute for Sustainable Development and International Relations, a nonprofit research institute based in Paris.
In the case of the United States, the study's most important finding is that it is technically feasible to reduce carbon dioxide emissions from fossil fuel combustion to 85 percent below 1990 levels. But that would require America's per-capita carbon footprint to plunge by an order of magnitude, with profound changes in energy systems.
Every country is different, but as the teams consulted with each other they developed "deep decarbonization pathways" that have three main elements in common.
These included increasing energy efficiency and conservation, above all else; producing more electricity with less carbon pollution through renewable energy, nuclear power or the capture and sequestration of emissions from burning fossil fuels; and replacing fossil fuels and transportation heating and industry with electricity, biofuels or hydrogen.
Another key lesson at this interim stage is to take a longer-term view—to consider steps to be taken out to the year 2050. Looking at near-term goals, they found, leads only to inadequate ambition.
But looking at long-term goals requires putting faith in some technologies that have not yet been perfected. And no matter how detailed and ambitious, these goals are not official pledges—they are just unsolicited advice to governments. So they could be seen as wishful thinking.
Canada's team confessed as much: "In order to reveal the technological pathways to deep decarbonization in Canada, current political realities were suspended," they wrote.
A Model Is Only a Model
It's been almost a quarter of a century since the nations of the world agreed in Rio to stabilize greenhouse gases at a level that would avoid the most dangerous consequences of man-made climate change.
Since then an enormous amount of economic modeling has gone to addressing the question of "whether the benefits of avoiding these risks outweigh the perhaps substantial cost of cutting emissions," said Simon Dietz and Nicholas Stern in a provocative new paper.
As early as 1991, path-breaking modeling by economist Bill Nordhaus on the optimum balance between costs and benefits produced a conclusion that has proved to have remarkable staying power: that only modest emissions reductions could be justified on economic grounds alone.
Stern, for his part, has staked his reputation on the thesis that much more ambition is needed—and that it can be supported by more nuanced economic analysis.
Nordhaus's model, Dietz and Stern argue, has built-in assumptions that "result in gross underassessment of the overall scale of the risks from unmanaged climate change."
So they tweaked the climate models to allow for the possibility that some damages from climate change would mount rapidly, especially as temperatures rise 4 degrees Celsius or more. And they give greater weight to the risk that the climate is more sensitive to CO2 than we might expect.
"We show that with the models extended in this way, business as usual trajectories of greenhouse gas emissions give rise to potentially large impact on growth and prosperity in the future, especially after 2100," they concluded. "Thus optimal emissions control is strong and strongly increasing."
In short, if you use the right yardstick, you'll end up setting the bar higher.
Better Than Sorry
A third study, by the Climate Action Tracker project, holds the Obama administration's latest crackdown against carbon pollution up against very ambitious targets—and finds the U.S. approach wanting.
It's not enough to set emission goals with a 66 percent probability of keeping the world within 2 degrees Celsius of warming, the authors hold. Better to be 85 percent sure.
They calculate that this would require all nations to achieve zero emissions of greenhouse gases between 2060 and 2080. Energy-related emissions of carbon dioxide would have to reach zero as early as 2045.
"Rapid and deep emissions reductions are not only necessary, but are feasible at a modest cost," their report said. "However, the window of opportunity to limit warming below 2 degrees Celsius could be closed by end of the 2020s unless action is accelerated."
This would require universal acceptance of highly ambitious targets. "The endeavor to stay below 2 degrees Celsius will not be achieved if individual agents advance their own interests independently."
As for the Obama administration's proposal to reduce emissions from existing power plants to 30 percent below 2005 levels by 2030, the report said it's too little and too late. Indeed, it would only slow, rather than hasten, the rate at which the United States has been decarbonizing in recent years.
At this pace, the United States won't meet its long-term pledge to reduce overall greenhouse gas emissions by 83 percent by 2050. And America wouldn't be doing its fair share toward making sure that the whole world doesn't warm more than 2 degrees Celsius, the report concluded.