Study finds warming caused by synthetic greenhouse gases could outweigh climate benefits from phasing down CFCs
An international team examining the total warming impact of 25 major synthetic greenhouse gases (SGHGs) has concluded that without additional limits on SGHG use, the resulting increase in warming could outweigh the climate benefits gained thus far from phasing down chlorofluorocarbons (CFCs). Their study is published in Geophysical Research Letters.
Chlorofluorocarbons (CFCs)—commonly used in refrigerators and air conditioners—play a role in creating a hole in the ozone layer over Antarctica. As these chemicals were phased-down due to international agreements limiting their use, they were replaced by other synthesized gases that can still be harmful to the ozone layer—and are also greenhouse gases that contribute to climate change. Despite this, synthetic greenhouse gases (SGHGs) beyond the CFCs have received relatively little attention up to now.
The researchers used measurements of SGHG levels from the Advanced Global Atmospheric Gases Experiment (AGAGE), a global observing system developed by Prinn and colleagues and sponsored by NASA and other agencies. The study team headed by Matthew Rigby, lead author and a research fellow at the University of Bristol, analyzed observed atmospheric levels of SGHGs from 1978 to 2012, and then used these measurements to predict the impact these gases could have on global warming through 2050.
In response to the phase-down of CFCs through the 1987 Montreal Protocol, the researchers discovered that the use of other synthetic gases as refrigerants—such as hydrofluorocarbons (HFCs)—has risen. HFCs had been limited in the now-defunct 1997 Kyoto Protocol, but there is currently no agreement restricting their use. So using HFCs as a test case, the researchers examined the effect of phasing down HFCs by amending the Montreal Protocol to include these gases.
Atmospheric measurements show that emissions of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons are now the primary drivers of the positive growth in synthetic greenhouse gas (SGHG) radiative forcing. We infer recent SGHG emissions and examine the impact of future emissions scenarios, with a particular focus on proposals to reduce HFC use under the Montreal Protocol. If these proposals are implemented, overall SGHG radiative forcing could peak at around 355 mW m−2 in 2020, before declining by approximately 26% by 2050, despite continued growth of fully fluorinated greenhouse gas emissions. Compared to “no HFC policy” projections, this amounts to a reduction in radiative forcing of between 50 and 240 mW m−2 by 2050 or a cumulative emissions saving equivalent to 0.5 to 2.8 years of CO2 emissions at current levels. However, more complete reporting of global HFC emissions is required, as less than half of global emissions are currently accounted for.—Rigby et al.
HFCs are particularly strong greenhouse gases, so even relatively small levels in the atmosphere can contribute to warming.
While HFCs are currently not a major driver of climate change compared to carbon dioxide or even other SGHGs, Ronald Prinn, co-director of the MIT Joint Program on the Science and Policy of Global Change and a co-author of the study, points out that if unabated they may contribute significantly to future warming.
Addressing HFCs, and other SGHGs, now will ensure that they don’t contribute significantly to warming in the future. CFCs have contributed the most among the synthetic greenhouse gases to warming. Their use peaked and levels are now declining, but these gases will remain in the atmosphere for many years. This is likely the trend we will see with most SGHG gases, so it is important that we address these gases now before they do more severe damage.—Ronald Prinn
Rigby, M., et al. (2014), Recent and future trends in synthetic greenhouse gas radiative forcing, Geophys. Res. Lett., 41, doi: 10.1002/2013GL059099