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After including these chemistry-climate modelled lifetimes into a Bayesian simulation model of production and emissions , the team was able to reduce the uncertainty in their lifetime estimates . They calculated the lifetimes for CFC-11 , 12 , and 113 to be 49 years , 85 years , and 80 years respectively , compared with current best values of 52 , 100 , and 85 years .
“ Because our estimates are shorter than current bestrecommended values , this implies emissions are likely higher than what best estimates have been ,” Lickley says .
To test this idea , the team looked at how the shorter CFC lifetimes would affect estimates of unexpected emissions , particularly between 2014 and 2016 . During this period , researchers previously identified a spike in CFC-11 emissions and subsequently traced half of these emissions to eastern China . Scientists have since observed an emissions decrease from this region , indicating that any illegal production there has stopped , though the source of the remaining unexpected emissions is still unknown .
When Lickley and her colleagues updated their estimates of CFC bank emissions and compared them with total global emissions for this three-year period , they found evidence for new , unexpected emissions on the order of 20 gigagrams , or 20 billion grams , for each chemical .
The results suggest that during this period , there was new , illegal production of CFC-11 that was higher than previous estimates , in addition to new production of CFC-12 and 113 , which had not been seen before . Together , Lickley estimates that these new CFC emissions are equivalent to the total yearly greenhouse gas emissions emitted by the United Kingdom .
It ’ s not entirely surprising to find unexpected emissions of CFC-12 , as the chemical is often co-produced in manufacturing processes that emit CFC-11 . For CFC-113 , the chemical ’ s use is permitted under the Montreal Protocol as a feedstock to make other chemicals . But the team calculates that unexpected emissions of CFC-113 are about 10 times higher than what the treaty currently allows .
“ With all three gases , emissions are much lower than what they were at their peak ,” Lickley says . “ But they ’ re very potent greenhouse gases . Pound for pound , they ’ re five to 10 000 times more of a global warming chemical than carbon dioxide . And we ’ re currently facing a climate crisis where every source of emission that we can reduce will have a lasting impact on the climate system . By targeting these CFCs , we would essentially be reducing some contribution to climate change .” RACA
This research was supported in part by VoLo Foundation .
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RACA Journal I August 2021 www . hvacronline . co . za