2013 extreme weather linked to climate change

A majority of 16 extreme weather events in 2013 have a climate change connection.

That's the conclusion from the latest attribution study published Monday from the Bulletin of the American Meteorological Society (AMS).

The AMS report concludes that 9 of the 16 extreme weather events studied have a climate change link. Which extreme weather events from 2013 have a clear climate change link?

AP Science Writer Seth Borenstein tallies where the events land in the study with respect to climate change:

Scientists looking at 16 cases of wild weather around the world last year see the fingerprints of man-made global warming on more than half of them.

Researchers found that climate change increased the odds of nine extremes: Heat waves in Australia, Europe, China, Japan and Korea, intense rain in parts of the United States and India, and severe droughts in California and New Zealand. The California drought, though, comes with an asterisk.

Scientists couldn't find a global warming link to an early South Dakota blizzard, freak storms in Germany and the Pyrenees, heavy rain in Colorado, southern and central Europe, and a cold British spring.

Organized by the U.S. National Oceanic and Atmospheric Administration, researchers on Monday published 22 studies on 2013 climate extremes in a special edition of the Bulletin of the American Meteorological Society.

"It's not ever a single factor that is responsible for the extremes that we see," said NOAA National Climatic Data Center director Tom Karl said. "Natural variability is always part of any extreme climate event."

For years, scientists said they could not attribute single weather events — like a drought, heat wave or storm — to man-made global warming. But with better computer models and new research, in some cases scientists can see how the odds of events increase — or not — because of climate change.

California Drought: Climate change fingerprints?

California's worst drought on record gets a split decision in this study, with some signs pointing to a climate change connection while others found no discernible link.

A Stanford University study found that climate change has made the likelihood of strong persistent high pressure ridges that cause drought three times more likely than in pre-industrial climates.

These ridges have been tagged Triple-R, or Ridiculously Resilient Ridges.

Climate scientist Noah Diffenbaugh of Stanford University and colleagues used a novel combination of computer simulations and statistical techniques to show that a persistent region of high atmospheric pressure over the Pacific Ocean--one that diverted storms away from California--was much more likely to form in the presence of modern greenhouse gas concentrations.

The result, published today in the Bulletin of the American Meteorological Society, is one of the most comprehensive studies to investigate the link between climate change and California's ongoing drought.

"Our research finds that extreme atmospheric high pressure in this region--which is strongly linked to unusually low precipitation in California--is much more likely to occur today than prior to the emission of greenhouse gases that began during the Industrial Revolution in the 1800s," says Diffenbaugh.

The researchers found that the extreme heights of the Triple R in 2013 were at least three times as likely to occur in the present climate as in the preindustrial climate.

They also found that such extreme values are consistently tied to unusually low precipitation in California, and to the formation of atmospheric ridges over the northeastern Pacific.

"We've demonstrated with high statistical confidence that large-scale atmospheric conditions similar to those of the Triple R are far more likely to occur now than in the climate before we emitted large amounts of greenhouse gases," Rajaratnam says.

Heat Waves: Strongest climate change signal?

The sharpest set of fingerprints linking extreme weather to climate change may be excessive heat events like the 2013 Australian heat wave. When the Australian Bureau of Meteorology has to add new colors to the weather map, you know it's an unprecedented heat event.

Mashable's Andrew Freedman has some perspective on how Australia's 2013 heat wave fits into the bigger climate change picture:

Regarding the heat in Australia, where the Bureau of Meteorology was forced to add a new color to its weather maps to show extremely hot temperatures up to 129 degrees Fahrenheit, the studies showed extremely low chances that the heat could have occurred without manmade global warming. One of the studies found the percent of risk of the event that could be attributable to manmade global warming to be "essentially 100%."

“The results from the Australian studies are rather striking,” said Peter Stott, the leader of the climate assessment team at the UK Met Office in Exeter, England.

Stott said the evidence shows that “it's very hard to imagine how you could have had those temperatures without global warming.”

September 2013 was the hottest September on record in Australia, and one of the studies found that the risk of such heat in September has jumped fivefold due to manmade climate change.

Scientists gain confidence in conclusions about extreme events when multiple studies use different methods, while arriving at similar conclusions. Five independent research teams looked at different factors related to the record heat in Australia in 2013, and each team came to the separate conclusion that human-caused climate change increased the likelihood and severity of that event. This raises scientists' confidence that global warming made the prolonged heat wave in Australia much worse.

"The evidence in the Australian papers is extremely strong," said Martin Hoerling, a researcher at the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, who was not involved in that research.

Overall, so called attribution studies are becoming more adept at finding links between climate change and individual extreme weather events. Many scientists believe as we change earth's climate, we essentially raise the 'base state' of what the atmosphere is capable of producing when it comes to extremes.

The analogy of a baseball player on steroids hitting more frequent, and longer home runs is often used. As humans inject increasing amounts of CO2 and other greenhouse gasses into our atmosphere, many scientists believe we are loading the potential for increasingly extreme weather events.

Just how much extreme weather is getting juiced by climate change is an ongoing and evolving area of climate science. The dangerous part of that evolution is that we may not know how much climate change is fueling extreme weather events with 100 percent certainty until the effects of these events become much more damaging and disruptive to our societies.