The international ban on ozone depleting chemicals could have unintentionally caused a slowdown in global temperature increases since the mid 1990s, according to a new study.
The so-called global warming hiatus has puzzled scientists. A recent theory, suggested in the Intergovernmental Panel on Climate Change’s (IPCC) latest review of the science, argues that temperatures have continued to rise, but that the heat has gone into the oceans.
Climate change deniers have also claimed the slowdown is evidence that the threat of global warming has been exaggerated.
When the Antarctic ozone hole was detected in 1985, researchers speculated that it was connected to increased levels of the organic compounds known as chlorofluorocarbons (CFCs), used in refrigerators and aerosols, in the atmosphere.
The Montreal Protocol was drafted to stop the depletion of the ozone layer. The treaty entered into force in 1989, and it is estimated that the ozone layer will repair itself by 2050 if the protocol is adhered to.
However, the new study, published in the journal Nature Geoscience, suggests that changes in the warming rate can be attributed to specific human actions.
CFCs also act as greenhouse gases, and the study’s authors suggest their prohibition could have had a global impact.
However, Felix Pretis, a statistician at the University of Oxford, said that the Montreal Protocol can’t on its own explain the reduced warming seen since 1998.
“While it has contributed to the warming hiatus, it does not entirely explain it”, he said.
“The impact of this change is small but not negligible: without the reduction in CFC emissions, temperatures today could have been almost 0.1C warmer than they actually are.”
The study also identified other periods of recent history when human action might have affected the rate of global warming.
The scientists say temperature increases slowed down during the two world wars and the Great Depression of the 1930s, when carbon dioxide emissions declined because of economic downturns.