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Anthropogenic Warming Goes Back to the 1930s

The past 16 record-breaking hot years globally have removed the doubts of world leaders about the influence of human-caused climate change, but the first signs appear as far back as 1937 according to research published in Geophysical Research Letters (

“Globally, all the record-breaking hot years we’ve had since the 1990s are so much outside natural variability that they would be almost impossible without climate change caused by humans,” said lead author Dr Andrew King of the ARC Centre of Excellence for Climate System Science.

“In Australia, our research showed the last six record-breaking hot years and last three record-breaking hot summers were made much more likely due to global warming,” King said. “We were able to see climate change more clearly in Australia because of its position in the Southern Hemisphere in the middle of the ocean, far away from the cooling influence of high concentrations of industrial aerosols.”

Previous research has shown that aerosols in high concentrations over specific regions had a cooling effect, reflecting more heat back into space. However, warming returned rapidly when those aerosols were removed from the atmosphere.

Cooling periods, likely caused by aerosols, occurred in Central England, Central US, Central Europe and East Asia during the 1960s and 1970s before accelerated warming returned. These heightened aerosol concentrations also delayed the emergence of a clear human-caused climate change signal in all regions studied except Australia.

“In regards to a regional human-caused climate change signal, Australia was the canary in the coal mine for the rest of the world. The signal appeared there first and then, over the coming years, it became apparent elsewhere,” King said.

“Recent increases in aerosols over East Asia has started to slow the rise in the number of the region’s record hot years and summers, again masking the clear climate change signal we are finding in other areas. High aerosol concentrations also significantly delayed the climate signal in the Central US.”

“The key now is to determine how much warmer the climate will continue to get so we can respond to the impacts this will inevitably bring,” said King. “This is particularly true for Australia, which appears to have one of the strongest climate change signals for a populated country. As a nation, it will need to respond more quickly and understand clearly what future climate change brings.”