Haze from coal and other fossil fuels dims the sky in Changchun, China.

Haze from coal and other fossil fuels dims the sky in Changchun, China.

Wang Zhe - ImagineChina

Feature: Choosing a climate future in Paris

(Editor’s note: The 27 November issue of Science explores the implications of the climate talks that begin in Paris this week. The introduction to the special feature section is reprinted below, followed by links to an informational graphic and additional stories.)

It’s reasonable to view the climate talks that begin this week in Paris with skepticism. More than 2 decades have passed since nations met in Rio de Janeiro to create the 1992 United Nations Framework Convention on Climate Change. Since then, a succession of international meetings under the Framework—most notably in Kyoto, Japan, in 1997 and Copenhagen in 2009—have done little to alter our planet’s worrisome trajectory. Annual global emissions of CO2 have risen steadily from 21 billion tons in 1992 to 32 billion tons in 2012. The rate of increase in the atmospheric concentration of greenhouse gases has accelerated, by roughly 30% since the 1990’s. Nine of the 10 warmest years on record have occurred since 1998, and the impacts of climate change are already being felt from the tropics to the poles.

Optimists point to the growing use of solar, wind, and other renewable power sources and the success of some nations, such as Denmark, in curbing emissions. But rising emissions from China, India, and other developing nations are swamping that progress. And the dismal track record of global climate talks inspires little confidence that nations can agree to make the huge changes required to stop treating the atmosphere like a carbon sewer.

Negotiators huddling in Paris next week are convinced these talks will be different. In Kyoto, nations attempted to create a legally binding agreement, which subsequently failed to deliver results in part because the United States would not ratify the treaty. This time, nations—164, as Science went to press—have each prepared pledges, called Intended Nationally Determined Contributions (INDCs), which detail their promised emissions cuts and other actions through 2030.         

Negotiators hope the bottom-up INDC approach will prevail where the top-down Kyoto strategy failed. Developing nations largely stuck to the sidelines in previous talks. This time almost everyone—including China and India—has pledged to curb emissions. And by arriving in Paris with pledges in hand, negotiators hope to avoid the last-minute deadlocks that have doomed past efforts.

That’s not to say that negotiators aren’t under pressure. There’s still the question of how developing nations will raise the tens of billions of dollars they’ll need to curb emissions and adapt to climate change. And it’s not clear how national pledges will be monitored and verified.

Another thorny question is whether nations will agree to review any Paris deal every 5 years. That would create regular opportunities for countries to extend their reduction policies past 2030 and ratchet up cuts. Climate experts say such action is needed, because the Paris pledges alone won’t keep planetary warming by 2100 below the 2°C ceiling that many consider safe.

The Washington, D.C-based nonprofit Climate Interactive, for example, estimates that without further action, the pledges will allow the world to warm 3.5°C by 2100. The U.N. Environment Program (UNEP), however, assumes that nations will extend their pledges, which could keep the warming to 2.7°C. The lower number is “a reason for hope,” says Cassie Flynn, a UNEP official, because it puts the 2°C threshold within reach—if nations can agree to work together after Paris.

Related content:

Infographic: After Paris: The rocky road ahead

Feature: In Denmark, a clean energy revolution

Feature: Can India keep its climate promises?

Policy forum: Can Paris pledges avert severe climate change?

Perspective: Understanding China's non–fossil energy targets

Editorial: Turning the focus to solutions

(Click on the infographic below to expand.)

CLIMATE INTERACTIVE; STRAUSS, B. H. ET AL. PNAS, (2015) ; ADAPTED BY A. CUADRA/SCIENCE; NATIONAL CLIMATE ASSESSMENT: NOAA NCDC/CICS-NC; SURGING SEAS RISK ZONE MAP, CLIMATE CENTRAL; BLOOMBERG NEW ENERGY FINANCE: NEW ENERGY OUTLOOK 2015; CLIMATE INTERACTIVE; VAN VUUREN, D. P., ET AL. CLIMATIC CHANGE 109.1-2 (2011); INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE; ADAPTED BY G. GRULLÓN/SCIENCE