Human influence on climate/hot years dates back to 1930s, new research finds

Humans have triggered the last 16 record-breaking hot years experienced on Earth (up to 2014), with our impact on the global climate going as far back as 1937, a new study finds.

The study suggests that without human-induced climate change, recent hot summers and years would not have occurred. 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 Andrew King, a climate extremes research fellow at the University of Melbourne, Australia and lead author of the study. “Recent record-breaking hot years globally were so much outside natural variability that they were almost impossible without global warming.”

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 yesterday in Geophysical Research Letters, a journal of the American Geophysical Union.

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.

“In Australia, our research shows the last six record-breaking hot years and last three record-breaking hot summers were made more likely by the human influence on the climate,” King said. “We were able to see climate change even 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.”

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 United States, 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.

The above post is reprinted from materials provided by American Geophysical Union.

Andrew D. King, Mitchell T. Black, Seung-Ki Min, Erich M. Fischer, Daniel M. Mitchell, Luke J. Harrington, Sarah E. Perkins-Kirkpatrick. Emergence of heat extremes attributable to anthropogenic influences.Geophysical Research Letters, 2016; DOI: 10.1002/2015GL067448

Other research from 2010-2012 found that monthly temperature extremes had become much more frequent, as measurements from around the world indicate. On average, there are now five times as many record-breaking hot months worldwide than could be expected without long-term global warming, shows a new study. In parts of Europe, Africa and southern Asia the number of monthly records has increased even by a factor of ten. 80 percent of observed monthly records would not have occurred without human influence on climate, the authors conclude.

2015 research said:  “Remarkably our research shows that you could already see clear signs of global warming in the tropics by the 1960s but in parts of Australia, South East Asia and Africa it was visible as early as the 1940s.”

The reason the first changes in average temperature and temperature extremes appeared in the tropics was because those regions generally experienced a much narrower range of temperatures. This meant smaller shifts in the temperature record due to global warming were more easily seen.

The first signal to appear in the tropics was the change in average temperatures. Later extreme temperature events showed a global warming signal.

Closer to the poles the emergence of climate change in the temperature record appeared later but by the period 1980-2000 the temperature record in most regions of the world were showing clear global warming signals

One of the few exceptions to this clear global warming signal was found in large parts of the continental United States, particularly on the Eastern coast and up through the central states. These regions have yet to manifest obvious warming signals according to the models but it is expected they will appear in the next decade.

Andrew D King, Markus G Donat, Erich M Fischer, Ed Hawkins, Lisa V Alexander, David J Karoly, Andrea J Dittus, Sophie C Lewis, Sarah E Perkins. The timing of anthropogenic emergence in simulated climate extremes. Environmental Research Letters, 2015; 10 (9): 094015 DOI:10.1088/1748-9326/10/9/094015