Wednesday, December 13, 2017

Three Things That Wouldn't Have Happened in 2016 without Climate Change

Bob Henson · December 13, 2017

“Impossible” is a fraught word, but a new set of studies concludes that at least three atmospheric and oceanic phenomena from 2016 wouldn’t have occurred had we not been adding greenhouse gases to the air for more than a century.

Record heat in Asia, record-high global temperature, and a marine “heat wave” in the far North Pacific are among 27 events analyzed in “Explaining Extreme Events in 2016 from a Climate Perspective.” This report, free to download in its entirety, is the sixth annual compilation of climate attribution studies published as a supplement to the Bulletin of the American Meteorological Society (BAMS). The 2016 report was released on Wednesday.


Record-high global temperature

Globally averaged surface temperatures hit a new high for the third consecutive year in 2016, leaving the much-disputed warming slowdown of the 2000s in the dust. A team led by Thomas Knutson (NOAA Geophysical Fluid Dynamics Laboratory) compared the 2016 value to all of the annual global temperatures calculated in an ensemble of more than 24,000 years of simulations from the Climate Model Intercomparison Project (CMIP5). All of these runs were for a “control” atmosphere—i.e., one in which greenhouse gases are kept at preindustrial levels.

The warmest peaks and valleys in the CMIP5 control runs were around 0.5°C above and below the midpoint. In contrast, the 2016 global temperature was roughly 1.3°C beyond the 1881-1920 average—thus more than twice as high as anything one would expect had we not been burning fossil fuels. Even if you add about 0.2°C to account for the volcano-induced cooling in 1881-1920, the 2016 warmth can’t be explained without climate change.


Numerous records were smashed in 2016 during prolonged heat waves across Asia. At least 580 people were killed by record-setting heat across India, and Thailand experienced its most prolonged heat wave in at least 65 years. A research team led by Yukiko Imada (Japan’s Meteorological Research Institute) found that extreme heat was more than twice as widespread across Asia in 2016 as it was during the runner-up year, 2010. The drying and warming effects of El Niño are partly to blame, but when calculating probabilities, the researchers found: “All of the risk of the extremely high temperatures over Asia in 2016 can be attributed to anthropogenic [human-caused] warming. In addition, the ENSO condition [El Niño] made the extreme warmth two times more likely to occur.”
[An El Niño occurs every two to seven years, so it does no make sense to claim it is the cause of record weather. It could make it more extreme than it would have been in another year.]


Among the other papers in this year’s BAMS report that found a climate-change link was a study led by Xing Yuan (Chinese Academy of Sciences). It examined the Yangtze River flooding in China, the year’s most expensive weather-related disaster. The floods cost $28 billion and claimed 475 lives. Yuan and colleagues found that human-caused climate change has increased the risk of the rains that led to the flooding by 17 – 59%. This risk increases further, to 37 – 91%, when El Niño is a factor, since the after-effects of an El Niño event in winter (as we saw in 2015-16) raises the odds of heavy rain in China in the subsequent summer.


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