Location and type of events analyzed in “Explaining Extreme Events of 2012 from a Climate Perspective.” Credit: NOAA

Human influences are having an impact on some extreme weather and climate events, according to the report Explaining Extreme Events of 2012 from a Climate Perspective released September 5, 2013 by the Bulletin of the American Meteorological Society. Scientists from NOAA served as three of the four lead editors on the report. Overall, 18 different research teams from around the world contributed to the peer-reviewed report that examined the causes of 12 extreme events that occurred on five continents and in the Arctic.

The report shows that the effects of natural weather and climate fluctuations played a key role in the intensity and evolution of many of the 2012 extreme events. However, in several events, the analyses revealed compelling evidence that human-caused climate change was a secondary factor contributing to the extreme event. “This report adds to a growing ability of climate science to untangle the complexities of understanding natural and human-induced factors contributing to specific extreme weather and climate events,” said Thomas R. Karl, LHD, director of NCDC. “Nonetheless, determining the causes of extreme events remains challenging.”

In addition to investigating the causes of these extreme events, the multiple analyses of four of the events—the warm temperatures in the United States, the record-low levels of Arctic sea ice, and the heavy rain in both northern Europe and eastern Australia—allowed the scientists to compare and contrast the strengths and weaknesses of their various methods of analysis. Despite their different strategies, there was considerable agreement between the assessments of the same events.

Thomas Peterson, PhD, principal scientist at NCDC and one of the lead editors on the report, said, “Scientists around the world assessed a wide variety of potential contributing factors to these major extreme events that, in many cases, had large impacts on society. Understanding the range of influences on extreme events helps us to better understand why extremes are changing." See more of what Dr. Peterson has to say on global warming and weather in this Climate Q&A from Climate.gov.