President Obama's reference to a super-greenhouse gas in his climate speech this week signals a growing realization within the administration of the importance of thinking beyond carbon for global warming solutions, analysts say.
Speaking at Georgetown University, Obama mentioned a recent agreement with Chinese President Xi Jinping to phase down hydrofluorocarbons (HFCs), a class of greenhouse gases up to thousands of times more powerful than carbon dioxide. When Secretary of State John Kerry went to India last week, HFCs were a high-level agenda item. And last year, the United States helped to spearhead a global coalition to cut short-lived climate forcers. Taken together, proponents of this strategy to slow the rate of climate change say, the efforts are significant.
"Policymakers are now only beginning to see that HFCs and other short-lived climate forcers are central, not tangential, to successful long-term climate mitigation," said Paul Bledsoe, a senior fellow at the German Marshall Fund and a former Clinton White House climate aide.
HFCs are gases with a variety of applications, from refrigeration and air conditioning to fire extinguishers. Since the Montreal Protocol was ratified in 1987 to control the expanding hole in the ozone layer, countries have been swapping chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) -- which eat away at the ozone -- for HFCs.
Although HFCs don't damage the ozone layer, they do accelerate global warming, especially in the short run. HFCs only stay in the atmosphere for about 15 years, while carbon dioxide can stay for up to 1,000 years. HFCs are considered to be "short-lived" climate forcers, along with methane, black carbon and stratospheric ozone.
Veerabhadran Ramanathan, a professor at the Scripps Institution of Oceanography at the University of California, San Diego, said action today will slow down climate change in the next few decades, while carbon dioxide will be the main driver of warming in the next century.
A paper published yesterday found that replacing HFCs with less-potent gases could avoid as much as half a degree Celsius of warming by the end of the century. Coupled with other short-lived climate warmers, it could avoid a temperature rise of 1.5 degrees Celsius by 2100.
"That's really, really big. That's comparable to the most aggressive CO2 mitigation strategy," said Durwood Zaelke, president of the Institute for Governance and Sustainable Development and one of the study's co-authors. "That's not just useful for a couple of decades; it's useful until the end of the century."
The International Energy Agency has said that the world is on track to warm by 5 degrees Celsius by the end of the century. While carbon regulations languish in the United States and global agreements stall in U.N. conferences, some say cutting short-lived climate warmers is the fastest, most efficient way to control climate change.
Competing estimates spark questions
But in the early stages of deciding how to replace HFCs, there are still many questions. Some gases have a global warming potential more than 4,000 times that of CO2, but others have a much smaller impact. These low-warming HFCs require more energy to use, ramping up CO2 emissions from fossil fuels, said Ramanathan, adding that there must be a balance among a gas's global warming potential, energy intensity and ozone depletion.
"We really need to take the whole picture of HFCs," he said. He argued that policymakers should focus on promoting replacements in the air conditioning and refrigeration sector first, as demand for fridges and air conditioners is expected to grow in developing countries.
But there's a cost factor. Honeywell International Inc. and DuPont Co. are developing three low-warming refrigerants that are expected to be significantly more expensive than existing refrigerants, said Lew Steinberg, president of Midwest Refrigerants, a company that breaks down the chemicals in HFCs, HCFCs and CFCs to resell to refrigerant makers.
And not everybody is bullish on curbing HFCs. Michael Prather, a professor of Earth system science at the University of California, Irvine, said the future estimates for the compound have been exaggerated.
"It's absolute hogwash," Prather said. He pointed to Intergovernmental Panel on Climate Change findings that HFC radiative forcing -- the measure of the capability of a gas to warm the Earth -- is currently less than 1 percent of the other major greenhouse gases. Therefore, he said, HFCs are only minimally responsible for the warming of the planet to date.
The study released yesterday in Atmospheric Chemistry and Physics relies on a model from a 2009 study by Guus Velders, one of the first to draw attention to the climate warming caused by HFCs and a co-author of the most recent study. In this model, future HFC radiative forcing reaches 30 to 40 percent of the total greenhouse gases. The IPCC's estimate: up to 6 percent.
Although Prather thinks HFC use should not increase, he said the conversion to HFC alternatives must consider all of the greenhouse gases.
"This is a crystal ball," he said of the Velders scenario. "We want to avoid the Velders world, but I don't know what the reality of that is."
Zaelke said the massive demand for refrigeration in China and India means the concentration is bound to be more than the IPCC estimate.
"I hope the lower numbers are right," he said. "But that's not what it looks like when you look out the window."
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