Human-caused climate change had impact in some extreme weather events from 2012: report

A recent report suggests that human-induced climate change had “little impact” on the 2012 drought in the U.S., but changes in sea level resulting from climate change have increased the probability of a once-in-a-century flood south of Atlantic City, N.J.

Bulletin of the American Meteorological Society published this week a special supplement containing 19 analyses by various researchers of 12 extreme weather events that occurred in 2012.

“The report shows that the effects of natural weather and climate fluctuations played a key role in the intensity and evolution of the 2012 extreme events,” according to an article posted to the website of the United States National Oceanic and Atmospheric Administration.

“However, in some events, the analyses revealed compelling evidence that human-caused climate change, through the emission of heat-trapping gases, also contributed to the extreme event.”

The supplement, titled Explaining Extreme Events of 2012 from a Climate Perspective, noted that the U.S. drought in 2012 “had become the most extensive since the 1950s, with more than half of all counties in the United States (spread among 32 states) listed as natural disaster areas by the U.S. Department of Agriculture.”

However the analysis concluded that human alteration of the composition of the atmosphere “may have had little effect on the frequency of low-precipitation periods.”

The researchers “hypothesize that if there are consequential changes to the hydrological cycle driving extreme dryness at seasonal scales, they will not be to rates of input, but to rates of output, via evaporative demand with increased surface warming.”

But 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,” according to the NOAA article describing the findings.

The supplement also discussed Hurricane Sandy, which “broke 16 historical storm-tide levels along the East Coast.”

A model used in the analysis “suggests that from Atlantic City southward, a once-in-a-century event or beyond in 1950 can now be expected to recur every couple of decades.”