Humans May Have Been Partly Responsible for 2017's Catastrophic Hurricane Season

Tropical Storm Harvey as seen from the International Space Station on August 28. NASA

The catastrophic, turbo-charged hurricane season of 2017 killed over 3,000 people and caused an estimated $250 billion in damage. Scientists now believe its intensity may, in part, have been the result of human activity.

In a study published in Science, Hiroyuki Murakami, associate research scholar at Princeton University, and colleagues analyzed the 2017 Atlantic hurricane season to work out what factors made it so intense—it ranked as the seventh most active season since records began in 1851. In total, there were 17 named storms. Ten of these went on to become hurricanes and six were major hurricanes.

Researchers used high-resolution computer models to look at the storms that hit between July 1 and November 30. They looked at the various factors that could have produced a more intense season. This includes La Nina, a phenomenon where water temperatures cool in the Pacific that has previously been linked to hurricane activity.

Findings showed that La Nina was not a major influencer. Instead, their models indicate local sea surface temperatures across the Atlantic were the driving factor. These anomalies saw the tropical Atlantic surface temperatures get warmer than the rest of the global ocean—and they correlated to the intensity of the season. The scientists wrote that while this could be the result of natural variability of the season, "it is also possible that greenhouse-induced global warming might have caused the emergence of the pronounced major hurricane activity."

Tropical Storm Harvey as seen from the International Space Station on August 28. NASA

The team also carried out simulation experiments using climate models to look at how hurricane intensity will change over time. Findings showed that increasing global temperatures and decreasing aerosol use (following the discovery of the hole in the ozone layer) will lead to a higher number of major hurricanes.

Murakami told Newsweek: "We found out that the last year's active major hurricanes were made due to combined effect of natural variability and anthropogenic forcing (decrease in aerosols and increase in greenhouse gasses). Although estimation for contributions from each component is difficult, impact of anthropogenic forcing cannot be neglected."

The team says more research will be needed to order to tease out the exact role of man-made activities on hurricanes. It is not possible to say whether Hurricane Florence, which recently hit the U.S. East Coast, was part of this trend. "[What] we can say from our study is that increase in anthropogenic forcing indeed increases frequency of intense hurricanes," Murakami said. "Therefore, it is possible that anthropogenic forcing contributes to the emergence of Hurricane Florence."

"Because reliable long-term observed tropical cyclone data is limited before satellite era, it is difficult to argue if the positive trend of intense hurricanes over recent years is due to anthropogenic forcing. The projected rate of increase in intense hurricanes by the climate model is also slow and the increase of intense hurricanes will be more significant toward the end of this century along with some variations caused by natural variability."

North Carolina Boardwalk In Hurricane Florence
Portions of a boat dock and boardwalk at Atlantic Beach, North Carolina, were destroyed by powerful wind and waves as Hurricane Florence arrived, on September 13. Chip Somodevilla/Getty Images

He did, however, say that nations need to prepare for major hurricanes to become a more regular feature—and scientists will need to assess the regional impact accordingly.

Daniel Horton, Assistant Professor in the Climate Change Research Group at Northwestern University, who was not involved in the study, said the findings show the need for better hurricane projections. "Extreme events, such as tropical cyclones, are complicated phenomenon as the formation of an extreme event requires a number of independent and sometimes co-dependent environmental ingredients," he told Newsweek.

"This study uses cyclone forecast models to investigate the influence of some of these ingredients and finds an outsized role for sea surface temperatures in the tropical Atlantic during the 2017 hurricane season. However, the study indicates that we are not yet able to determine the cause of the abnormally warm tropical Atlantic ocean waters in 2017, and speculates that the underlying causes may be due to human causes, natural causes, or most likely, some combination thereof.

"It further indicates that projections of future hurricane season activity in our warming world are made difficult by the large underlying natural variability of tropical cyclone ingredients."

Humans May Have Been Partly Responsible for 2017's Catastrophic Hurricane Season | Tech & Science