Atmospheric concentrations of a greenhouse gas nearly 13,000 times more potent than carbon dioxide rose faster than ever before over a three-year period starting in 2015, a new study has found. The findings suggest that China and India may not be living up to recent pledges to dramatically reduce emissions of the pollutant.

The gap between the two countries' voluntary pledges to reduce the greenhouse gas—known as HFC-23, a type of hydrofluorocarbon—and the estimates of actual emissions for the pollutant is the equivalent of approximately 103 million metric tons of carbon dioxide per year, or the annual greenhouse gas emissions of 22 million automobiles, according to the U.S. Environmental Protection Agency.

HFC-23 is an unwanted byproduct resulting from the manufacturing of HCFC-22, a chemical used in refrigeration and air conditioning. HCFC-22 replaced chlorofluorocarbons, which were phased out beginning in the 1990s for their role in creating the so-called "ozone hole." Since the international ban began, under the Montreal Protocol, atmospheric ozone concentrations have increased, and is expected to lead to the full recovery of the ozone layer sometime in the middle of the century.

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A 2016 addition to the Montreal Protocol, known as the Kigali Amendment, requires companies that manufacture HCFC-22 to destroy HFC-23 to prevent its release into the atmosphere. So far, the United States, China and India have not ratified the agreement. The Trump administration's failure to ratify the Kigali Amendment, despite strong support from U.S. industries, takes pressure off of other countries to do the same, Avipsa Mahapatra, the climate campaign lead for the Environmental Investigation Agency (EIA), a UK-based environmental organization, said.

"At the end of the day," Mahapatra said, "we have seen time and again that we do need strong international political will, as well as enforcement to ensure that egregious emissions do not continue to harm our ozone layer and also the climate."

Beginning in 2015, China and India set ambitious targets to dramatically reduce HFC-23 emissions. The two countries account for 75 percent of all HCFC-22 produced globally, and their emissions reduction programs should have resulted in an 87 percent drop in HFC-23 emissions from 2014 to 2017, according to the study. Instead, atmospheric concentrations continued to increase.

"What we should have seen in the atmospheric data was the concentrations stop growing and stabilize over the course of three years," said Matthew Rigby, an atmospheric chemist at the University of Bristol, and lead author of the new study. "But what we actually saw when we looked at the data, was that the concentrations were still going up and they were going up faster than they have before." The study was published Tuesday in the journal Nature Communications.

The findings are especially troubling because of the extremely low cost of readily available technology to eliminate emissions of the greenhouse gas, environmental advocates say.

Mahapatra said she wasn't surprised by the increased emissions reported in the current study.

"What is surprising is that there is as massive a discrepancy between what is being reported versus what is being seen in the atmosphere," Mahapatra said. "I would call it a massive environmental climate crime for any company or country to be knowingly venting these super potent greenhouse gases."

Air conditioners and refrigerators are cooled using the hydrofluorocarbon HCFC-22. An unwanted byproduct of the manufacturing of this refrigerant is HFC-23, which is a greenhouse gas nearly 13,000 times more potent than carbon dioxide. Credit: STR/AFP via Getty Images

Emissions of HFC-23 could be eliminated almost entirely with existing, low-cost technology, as previous emission reduction efforts have shown, making it one of the least expensive methods to address climate change.

"This is the top of the list of low hanging fruit because it's easy and inexpensive to do," Alex Hillbrand, an HFC specialist with the Natural Resources Defense Council's climate and clean energy and international programs, said.

Climate policy analysts measure emissions of greenhouse gases in carbon dioxide equivalents, or the amount of pollutant that would have the same impact on the climate as a given amount of carbon dioxide. Because HFC-23 is such a potent greenhouse gas, a relatively small amount equals a much larger amount of carbon dioxide.

HFC-23's potency means its emissions, and efforts to reduce those emissions, have an outsized impact on global warming compared to carbon dioxide. Incinerators installed at chemical production plants can destroy HFC-23 emissions for approximately $0.26 per ton of carbon dioxide equivalent, according to a 2017 study by the Institute for Applied Ecology in Germany. By comparison, efforts to reduce CO2 are much costlier. For example, two GOP-led plans calling for a price on carbon would start at $15 to $40 per ton of carbon dioxide equivalent and increase to as much as $115 per ton of CO2 equivalent by 2030.

"It's really one of the cheapest options, and the reason is HFC-23 has such a high global warming potential," said Lambert Schneider, research coordinator for international climate policy at the Institute for Applied Ecology, who helped develop an international carbon trading system in the early 2000s for the reduction of HFC-23 emissions from plants in China, India, South Korea, Argentina and Mexico. "For each ton you burn, you get approximately 12,000 carbon credits."

The low cost of eliminating HFC-23 emissions relative to prices placed on carbon under different carbon trading systems, has proven problematic for earlier efforts to eliminate HFC-23 emissions.

The emissions trading system that Schneider helped develop, the Clean Development Mechanism of the Kyoto Protocol, was so effective at providing incentives for HFC-23 incineration, it created a kind of "perverse incentive." Chemical plants were producing more HCFC-22 than necessary just so that they could burn off more HFC-23 and earn additional carbon credits. As a result, the European Union, the largest backer of the Clean Development Mechanism, stopped buying credits under the carbon trading system in 2013.

The EIA warned in 2013 that the EU's decision to stop purchasing credits for the carbon trading program would result in a massive increase of HFC-23 emissions. An investigation by the group found that chemical plants in China that were not covered under the carbon trading system were venting HFC-23 into the atmosphere, and those that were covered planned to stop incinerating and begin venting when the program's funding dried up.

Mahapatra cautioned that the sources of the additional emissions remain unknown. Emissions could, for example be coming from HCFC-22 production facilities in China that Chinese officials are not aware of. That was the case with a recent spike in emissions of CFC-11, a potent greenhouse gas and ozone-depleting chemical banned under international agreements.

Stephen Montzka, a National Oceanic and Atmospheric Administration researcher who first drew attention to the increase in CFC-11 emissions, noted that while China and India are the likely sources of the recent increase in HFC-23 emissions, additional studies will be required to pinpoint their exact origins. Rigby, the author of the current study, said he hopes to complete a follow-up study before the end of the year to try to determine more precisely where the emissions are coming from.