The latest report from the main international panel charged with assessing climate change, released today in Copenhagen, shouts the same basic message scientists have been telling governments for decades.
Protecting the planet will require a dramatic shift away from fossil fuels, the report from the Intergovernmental Panel on Climate Change emphasizes.
The release was timed for political impact, arriving weeks before international negotiators meet in Lima, Peru, to start forging a new strategy on climate change.
"Science has spoken. There is no ambiguity in their message," United Nations Secretary-General Ban Ki-moon said in a news conference this morning in Copenhagen. "Leaders must act; time is not on our side."
The Fifth Assessment Synthesis Report, as it's called, pulls together the conclusions of three IPCC working groups, which issued reports over the past year on the underlying science, the impacts, and the ways to address climate change.
Prepared by hundreds of scientists from around the globe, it's a statement of the scientific consensus aimed at the people in government who might do something about climate change.
"To avoid the chaos of runaway climate change, we know that we need to dramatically reduce global emissions of greenhouse gases," Rajendra Pachauri, the panel's chairman, said at the news conference.
Here are a few takeaways:
1. Evidence that Humans Are Causing It Is Stronger.
It's "extremely likely," the report says, that human influence, primarily the burning of fossil fuels, has been the dominant cause of global warming over the past several decades. That's stronger language than the previous version of this report, released in 2007, which concluded that it was merely "very likely." In the oddly precise IPCC lingo, that one-word change stems from a 5 percentage point increase in scientific certainty, from 90 to 95 percent.
2. The Forecast for 2100 Is . . . Challenging.
If the direness of the forecast could be measured as precisely as its certainty, you'd probably have to say that it has increased by more than 5 percentage points since 2007. Without urgent action to slash greenhouse gas emissions, the new report says, "warming by the end of the 21st century will lead to high to very high risk of severe, widespread, and irreversible impacts globally."
There was nothing quite like that statement the last time around.
An example of an "irreversible impact" would be passing the point of no return for the West Antarctic Ice Sheet—the point beyond which all we can do is hope its collapse into the sea, and the resulting 10- to 13-foot (3- to 4-meter) rise in sea level, will be slow. Some scientists think that at least some parts of the ice sheet already have begun to collapse.
Another kind of irreversible impact would be extinction of plants or animals. "A large fraction of species faces increased extinction risk due to climate change" during this century and beyond, the new report says.
3. It's Happening Now.
Compared to the 2007 assessment, the report includes stronger evidence of the many ways the planet is already experiencing the effects of human-caused climate change—sea-level rise, shrinking glaciers, decreasing snow and ice cover, warmer oceans and more frequent and intense extreme weather events, such as heat waves in Europe, Asia, and Africa, and heavier rain- and snowstorms in North America and Europe.
If the litany sounds familiar, that's because it is.
"It's just a bit firmer version of the same diagnosis that was given seven years ago," said Duke University climate scientist Drew Shindell, who co-authored one of the three working group reports. "The main problem is people didn't like the prescription."
4. What's Needed Now Is . . . Politics.
Actually, politics enters into the production of the IPCC report itself. Although it's a statement of scientific consensus, the crucial 40-page "summary for policymakers" has to be approved by the policymakers themselves. Over the last five long days in Copenhagen, the scientists and representatives of the world's governments have been debating and editing it line by line.
"Anything that's politically contentious gets stripped out of the summary for policymakers," said David Victor, professor of international relations at the University of California at San Diego and an author of a working group report.
This year, for example, research showing the problems with the 1997 Kyoto Protocol and why it failed to achieve greater emissions reductions were included in the scientists' report but did not make it into the summary.
"The diplomatic community would like to believe that what they've been doing has had a bigger impact, so it would have been a kick in the pants," Victor said. "Because it would have been a kick in the pants is one of the reasons it's not in there."
Also left out was a box that explained in one place how much temperature increase would create the kind of dangerous climate change that world leaders pledged to avoid in the only climate change treaty the United States has signed, the United Nations Framework Convention on Climate Change.
Michael Oppenheimer, a Princeton geoscientist and lead author of one of the scientific reports, called the omission a "disappointment." He pointed out that all the information in the box is already elsewhere in the report, but now policymakers will be forced to dig around to find it.
"I think it's a reflection of the difficulties countries have had agreeing on what to do about the climate change problem," Oppenheimer said.
The science has long been clear enough.
"Every time the IPCC comes around, we have a crisper more worrisome set of messages about the trends in emissions and impacts of climate change, and then you don't see much connection between that story and what governments actually do," Victor said. "That's because it's not really a scientific problem anymore. Essentially, everything that needs to be done to move the needle is political."
In 2009, on the heels of the previous IPCC report, the world's political leaders took their last serious stab at moving the needle at another conference in Copenhagen, where the latest IPCC report was just released. Those talks collapsed like a melting ice sheet.
Since then greenhouse gas emissions have continued to rise on the same trajectory, as have concentrations of greenhouse gases in the atmosphere.
5. But There's Still Paris.
If "Copenhagen" has become a synonym for "debacle" in the community of climate negotiators, "Paris" has become the glimmer of hope.
"I'm confident we can make it happen," Ban said about the prospect of a new international climate pact. The IPCC operates under the auspices of the UN.
In six weeks, the negotiators will gather in Peru. That meeting is supposed to prepare the way for the conference in Paris in December 2015, which aims to reach an agreement to replace the Kyoto Protocol. Kyoto required developed countries to reduce greenhouse gas emissions by specific amounts. It was a legally binding treaty—except that it never bound the United States, then the largest emitter, which never ratified it. And it never bound China, now the largest emitter, because all developing countries were exempt.
The argument between developed and developing countries—about who should do how much to "mitigate" climate change through reduced emissions—has always been one of the main obstacles to an agreement that actually makes a difference. But the chasm is less deep than it used to be, said Laurence Tubiana, the French diplomat charged with organizing the Paris conference.
"All countries, including less developed countries, are saying their contribution will have a mitigation part," Tubiana said on a visit to Washington last month. "Even Mali will have emissions reductions. That's really unprecedented."
Developed countries, for their part, might start delivering soon on their commitment to create a Green Climate Fund to help less developed countries. France and Germany each have pledged $1 billion to the fund, which has a staff and a headquarters outside Seoul. At a meeting in Berlin this month, other countries are expected to step up to the plate.
So much for signs of hope. They're small compared with the task. At Copenhagen in 2009, while the negotiators were failing to agree on measures to stop climate change, they did at least agree on a target: The global average temperature should not be allowed to rise more than 2°C (3.6°F) above preindustrial levels.
The 2°C target has been criticized lately, including by Victor. But to Tubiana, "it's just crazy" to talk about abandoning that target. "We'll be very strong on this—2 degrees should be the anchor," she added.
To keep warming below 2°C, according to the new IPCC report, the world will have to cut greenhouse gas emissions between 40 and 70 percent by 2050—and then keep cutting until they're essentially zero by 2100.
Coal and natural gas would need to be phased out for electricity use, unless technologies are developed to capture and store the carbon dioxide they emit.
The report says transforming the global energy industry will be affordable-at a cost of about 0.06 percent of global consumption growth per year-if actions are taken soon.
"The costs will go up enormously if we keep delaying things," said Pachauri. "The cost of inaction will be horrendously higher than the cost of action."
There's no consensus on what type of agreement might accomplish that, except that it's not likely to be a legally binding treaty that commits each country to specific emissions cuts. In a talk at the Brookings Institution, a Washington think tank, Tubiana spoke of a possible Paris agreement in carefully fluid terms.
"What does it mean, Paris?" she said. "It means sending a very strong signal to the business sector," the way the U.S. Federal Reserve does when it adjusts interest rates. Negotiators in Paris, Tubiana said, will "have to create a self-fulfilling prophecy that the low-carbon economy is happening . . . How we produce the signal is the challenge of Paris."
Will the new IPCC synthesis report help? It won't convert climate change skeptics or change national negotiating positions, said Robert Stavins, an environmental economist at Harvard University and a lead author of the report.
"Rather than changing people's minds, it serves as ammunition, with which they can support their previously established positions," said Stavins. "That doesn't mean it's not relevant, because it requires ammunition to win a battle."
"There's enormous fatigue with this," Tubiana said. "Everybody is fed up. We have to deliver now."