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Aa society, we are only now beginning to understand the emotional, physical and economic toll of recent catastrophic events such as hurricanes Harvey and Irma, says Auburn University climate scientist Hanqin Tian.

This past August, the National Oceanic and Atmospheric Administration, or NOAA, had forecasted the likelihood that 2017 would be an above-normal hurricane season with 14 to 19 named storms and two to five major hurricanes within the Gulf of Mexico, Atlantic and Pacific oceans.

Tian says what is abnormal about this season is the formation of five named hurricanes—Harvey, Irma, Jose, Katia and now Maria—all within four weeks. Furthermore, there hasn’t been an instance where three hurricanes occurring in the Atlantic basin simultaneously since 2010, according to NOAA.

Tian leads Auburn’s Climate, Human and Earth System Sciences, or CHESS, strategic cluster and is director of the International Center for Climate and Global Change Research in Auburn’s School of Forestry and Wildlife Sciences.

He and fellow scientists point to a combination of factors which contribute to increased frequency of hurricanes, including higher sea surface temperatures than normal; a weak or non-existent El Nino; weaker trade winds; more conducive wind patterns coming off Africa; a stronger west African monsoon; and average or weaker-than-average vertical wind shear in that same region.

“Multiple lines of scientific evidence have shown that Earth’s ecosystems and our economic system are very vulnerable to the adverse impacts of climate change, and are already experiencing increased impacts of persistent extreme weather events such as droughts and hurricanes, heat waves and sea-level rise,” said Tian.

Auburn climatologist and physical geographer Chandana Mitra, an associate professor in the College of Sciences and Mathematics, elaborated on the factors influencing hurricane frequency.

“Strong El Ninos and wind shear typically suppress development of Atlantic hurricanes, so the prediction for weak conditions points to more hurricane activity this year,” said Mitra. “Also, warmer sea surface temperatures tend to fuel hurricanes as they move across the ocean.”

Based on these existing conditions, the intense frequency of this year’s hurricanes can be attributed to a mixture of complex weather and climatic elements that impact the system uniquely.

The Auburn scientists say when we separate natural variable occurrences—such as wind shear, strong African monsoon events and the lack of El Nino—the trending above normal warm water temperature of the Atlantic is an anomaly from normal climatic phenomenon.

There is a heated debate playing out in the media regarding the correlation between global warming and increasing hurricane activities in the North Atlantic.

One side of this debate insists the increase in hurricane activities is part of the natural weather variability, while the other side suggests there is a strong correlation between the upward trend of hurricane activity and sea surface temperature increasing, which many researchers believe is caused by increasing greenhouse gas emission.

The National Academy of Sciences, a private, nongovernmental institution established by Congress to advise the nation on issues related to science and technology, states, “Theoretical and modeling assessments consistently point toward an increase in hurricane intensity with global warming. For the North Atlantic, the annual number of the most intense hurricanes has been predicted to increase by more than 50 percent for each degree Celsius increase in surface temperatures.”

Regardless of cause or frequency, many scientists agree a greater discussion must occur that addresses and seeks to mitigate societal impacts and economic losses that occur from aberrant weather events such as catastrophic hurricanes.

Economists with Moody Analytics estimate that our recent hurricanes, Harvey and Irma, have caused $150 billion and $200 billion in damages to Texas and Florida, respectively. These figures include damage to homes and furnishings, vehicles, commercial real estate and public infrastructure.

Long-term impacts of flooding and wind damage on local economies due to loss of productivity, operational changes and population shifts are less certain and could be permanent. U.S. population trends directly influence the degree of losses from extreme weather events. There are more people in harm’s way, more property in harm’s way due to increased wealth in areas of greatest risk such as coastlines, and social vulnerabilities within populations.

“The poor and elderly, for example, may not have the means to mitigate against tropical cyclone risks,” said Christopher Burton, assistant professor of geosciences. “One viable way to move forward is to address vulnerability and the resilience of populations in order to reduce tropical cyclone losses.”

“The U.S. ecosystems and our economic system are already experiencing increased impacts of hurricanes and tropical storms,” Tian added.

“To develop the knowledge and strategies effectively for responding to the risks of hurricanes and tropical storms as well as restoring the impacted ecosystems and economic systems, is of critical importance to adopting a coupled climate-human-earth system approach and engaging policy makers and the public.”