U.S. Navy
Superstorm Sandy (damage shown above) was not in itself caused by climate change, but rising sea levels contributed to the severity of the surge and thus caused more damage, a new report says.

Hot Tip: Report Reveals Man-Made Causes of Extreme Weather

September 05, 2013

Among the global-warming naysayers are those who admit that Earth’s climate is changing, but argue that it is part of a natural process that would be happening with or without human activities.

Now scientists at the National Oceanic and Atmospheric Administration (NOAA) have finished analyzing the extreme weather events of 2012 and sorted out some of what is our “fault” from what is happening on its own. The answer, as with most polarized debates, is that the truth lies somewhere in the middle, and the relationships between the dynamics are complex. Nonetheless, many of the factors influencing the severity of events can be traced back to human activity, NOAA said in a statement on September 5.

In the peer-reviewed report, using data from 18 research teams around the world, NOAA examined the causes of 12 extreme events that occurred on five continents and in the Arctic during 2012, the agency said in a statement. The studies, published as a special supplement in the Bulletin of the American Meteorological Society, highlighted the ways that human activity did, and did not, appear to influence weather and climate events.

For example, when it came to heat wave and drought, the report found that human-caused climate change did not have much influence over how much precipitation fell during 2012. But it did factor into the amount of warmth and the likelihood of heat waves such as those that blanketed the U.S. this past spring and summer.

“High temperatures, such as those experienced in the U.S. in 2012 are now likely to occur four times as frequently due to human-induced climate change,” NOAA said. “Approximately 35 percent of the extreme warmth experienced in the eastern U.S. between March and May 2012 can be attributed to human-induced climate change.”

Likewise, while Superstorm Sandy’s impact was primarily due to the massive storm surge brought on partly by high tides, the surge came as far inland as it did because of increased sea levels stemming from human-induced climate change, NOAA said.

“Ongoing natural and human-induced forcing of sea level ensures that Sandy-level inundation events will occur more frequently in the future from storms with less intensity and lower storm surge than Sandy,” the statement said.

Melting Arctic sea ice and global rainfall offered similar relationships, with the extremely low ice extent of summer 2012 coming mainly from the melting of younger, thin ice as it interacts with a warmed atmosphere and ocean, NOAA said.

“This event cannot be explained by natural variability alone,” NOAA said. “Summer Arctic sea ice extent will continue to decrease in the future, and is expected to be largely absent by mid-century.”

Global rainfall, most notably the intense rains that fell on the United Kingdom in 2012, came from natural variability, NOAA said. But the totals may have been “influenced by increases in sea surface temperature and atmospheric moisture which may be linked to human influences on climate,” the climate agency said.

"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, L.H.D, director of NOAA's National Climatic Data Center, in the statement. "Nonetheless, determining the causes of extreme events remains challenging."