Source of the sizzle: Climate change fueled heat waves

Climate change influenced several of the world's most extreme weather events of 2013, including heat waves in Australia, Europe, China, Japan and Korea, says a series of studies out Monday in the Bulletin of the American Meteorological Society.

Though links between global warming and events such as droughts and heavy rainfall were not obvious, connections were clearest with extreme heat: An analysis of five extreme heat events overseas "overwhelmingly showed that human-caused climate change is having an influence," according to the report.

Australia endured its hottest year ever recorded in 2013, which helped fuel several outbreaks of ferocious wildfires.

Overall, the report, "Explaining Extreme Events of 2013 from a Climate Perspective," addressed the causes of 16 individual extreme events that occurred on four continents in 2013. It was organized by the National Oceanic and Atmospheric Administration (NOAA).

Extreme events are often complex and influenced by multiple factors, said Thomas Karl, director of NOAA's National Climatic Data Center and report co-author at a press briefing on Monday.

Natural variability is always part of any weather and climate extreme, and pinpointing the human influence for an event is not always found in these studies, he said.

"It's a granted that climate change is influencing all manner of weather," according to NOAA research meteorologist Martin Hoerling. "This report looks not if climate change influenced weather, but how it did – trying to quantify the influence," Hoerling said at the press briefing.

For the intense drought currently afflicting California, which was investigated by three U.S. science teams, human factors were found not to have influenced the lack of rainfall, the report found.

However, though no direct link could be made with the lack of rain, the atmospheric conditions associated with the drought are "very likely" linked to human-caused climate change, according to Noah Diffenbaugh, a Stanford University climate scientist who contributed to a study in the report.

"This annual report contributes to a growing field of science which helps communities, businesses and nations alike understand the impacts of natural and human-caused climate change," Karl said.

This is the third year this type of report has been produced.

"The science remains challenging, but the environmental intelligence it yields to decision-makers is invaluable and the demand is ever-growing," Karl said.

"This is one approach to analyze a potential effect of global warming on different kinds of extreme events," said Peter Hoeppe, head of Munich Re's Geo Risks Research. Hoeppe, who was not involved in the report, is with Munich Re, the world's largest reinsurance firm.

"It is important to have studies like this to raise awareness on changes in weather patterns and their effects, and to find explanations for the processes behind them," he added.

"However, analyzing only the events of one year has the risk that one just picks an extreme year, which would also have been extreme without climate change," Hoeppe said. "I believe that a long term (at least 30 years) statistical analysis of extreme weather events has to back these statements."