A story on the BBC news website today reports that a study into a so-called pause in global warming has linked it to a ban in chemicals which are harmful to the atmosphere.
An article published in Nature Geoscience suggests that the ban of chloroflurocarbon compounds, or CFCs, is responsible for the standstill in global temperatures since the late 1990s.
CFCs were originally banned because of their depletion of the ozone layer. Since CFCs are notoriously unreactive (a property which was considered an advantage in their early applications), they can reach the upper atmosphere, where the Earth’s UV light cause bond scission to give a chlorine radical, e.g:
CCl3F → CCl2F. + Cl.
This radical catalytically transforms ozone into dioxygen, and one chlorine radical can deplete thousands of ozone molecules before finally leaving the atmosphere.
Furthermore, CFCs were found to also have a significant warming effect on the atmosphere, contributing thousands of times more to the Greenhouse Effect than carbon dioxide. Unfortunately, CFCs can have a lifetime of 100 years, and so they can have devastating effects on the environment.
This latest study suggests that a stall in global temperatures coincides with the introduction of the Monreal Protocol, which phased out the commercial use of CFCs in 46 countries in 1987. The authors also point out that while emissions were reduced during events such as world wars, global temperatures also slowed down.
Unfortunately, it is very difficult to conclusively prove what the causes of global temperatures are, with many different contributing factors being possible. It seems very plausible that a reduction in CFC emissions would lead to a positive effect on global temperatures, but could this alone cause global warming to reach a standstill? Indeed, Felix Pretis and Prof. Myles Allen from the University of Oxford say that the CFC ban is “unlikely to be the whole story”.
The phasing out of CFCs is certainly a new factor to consider in the study of our global temperature but, personally, I’m quite skeptical as to whether it’s possible to draw such a sweeping conclusion on such a complex topic. In my opinion, this is just one piece of the global warming puzzle, and there is still a lot of work to do before it can be solved.