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Issue #1723      March 16, 2016

Human caused global warming detected in 1930s

The last 16 record-breaking hot years globally clearly show the influence of human caused climate change with the first signs appearing as far back as the 1930s, according to new research published today 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, from the ARC Centre of Excellence for Climate System Science*.

But even at country and regional scales, where it is often much harder to detect global warming signals, the influence of human caused climate change still became unmistakable in many regions in the 1990s and for Australia as far back as 1980.

“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,” said lead author, Dr King.

“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, when those aerosols were removed from the atmosphere, the warming returned rapidly.

This cooling impact was seen very clearly by the researchers when they looked at five different regions, Central England, Central Europe, Central US, East Asia and Australia.

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,” Dr 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.” To get their results the researchers took a new approach. In the past, most researchers searching for a human caused climate change signal selected specific events and then tried to determine the role of climate change in those events.

By contrast, this study looked at when events started exceeding the range of natural variability. Using climate models, they looked at a world without human produced greenhouse gases and compared it to a world where the composition of the atmosphere corresponded with those found over time in the real world.

Where real world observations rose above the range of natural variability produced in climate models showing temperatures in a world without industrial activity, this indicated the unequivocal influence of human caused global warming.

“Everywhere we look the climate change signal for extreme heat events is becoming stronger. 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 Dr 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.”

Key Facts and Figures

  • The last 16 hottest years on record globally were all influenced by climate change.
  • The first signs of global climate change in heat records appeared in the 1930s.
  • Of the five regions analysed, Australia was most sensitive to global warming.
  • Global warming in annual heat records was detectable in Australia as far back as 1980.
  • The last six record-breaking hot years in Australia were likely due to global warming.
  • The last three record-breaking hot summers in Australia were like due to global warming.
  • The year global warming was first clearly detected in temperature records for each region studied was: Australia – 1980; Central Europe – 1989; Central England – 1990; East Asia – 1990; Central US – 2012

The ARC Centre of Excellence for Climate System Science is the largest university-based climate research centre in the Southern Hemisphere. It is funded by the Australian Research Council. The Centre is an international research consortium of five Australian universities and a suite of outstanding national and international Partner Organisations.

The Centre was established in 2011 with extensive investment from the Australian Research Council, the University of New South Wales, the federal Department of the Environment, New South Wales Government, Monash University, the Australian National University, the University of Melbourne, and the University of Tasmania. It has strong links with the Australian Community Climate and Earth System Simulator (ACCESS) initiative and works in partnership with the National Computational Infrastructure (NCI) Facility.

The Centre’s focus, Climate System Science, is the quantitative study of the climate system designed to enable modelling of the future of the climate system. It is built on a core of the sciences of the atmosphere, ocean, cryosphere and land surface.

Next article – Gardener’s Tale

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