Sydney, Mar 9: Humans have triggered the past record-breaking hot years experienced on the Earth since 1930s, says a study that suggests that without human-induced climate change, recent hot summers and years would not have occurred.
According to the new study, record-breaking hot years attributable to climate change globally are 1937, 1940, 1941, 1943-44, 1980-1981, 1987-1988, 1990, 1995, 1997-98, 2010 and 2014.
The researchers also found that this effect has been masked until recently in many areas of the world by the wide use of industrial aerosols, which have a cooling effect on temperatures.
"Everywhere we look, the climate change signal for extreme heat events is becoming stronger," said lead author of the study Andrew King of the University of Melbourne, Australia.
"Recent record-breaking hot years globally were so much outside natural variability that they were almost impossible without global warming," King noted.
The researchers examined weather events that exceeded the range of natural variability and used climate modelling to compare those events to a world without human-induced greenhouse gases.
The study was accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
Aerosols in high concentrations reflect more heat into space, thereby cooling temperatures. However, when those aerosols are removed from the atmosphere, warming returns rapidly.
The researchers observed this impact when they looked at five different regions: Central England, Central Europe, the central United States, East Asia and Australia.
There were cooling periods, likely caused by aerosols, in Central England, the central US, Central Europe and East Asia during the 1970s before accelerated warming returned, and aerosol concentrations also delayed the emergence of a clear human-caused climate change signal in all regions studied except Australia, according to the study.
"In regards to a human-induced climate change signal, Australia was the canary in the coal mine for the rest of the world," King said.