The National Science Foundation has closed its investigation into Pennsylvania State University climatologist Michael Mann after finding no evidence of scientific misconduct related to his research, the Daily Climate reports.

It is the latest in a string of investigations to exonerate scientists involved in the so-called "Climategate" email scandal.

Mann was a central figure in the fracas, where a sampling of correspondence from climate scientists purloined from a computer server at the University of East Anglia in Britain supposedly showed climate scientists colluding to fabricate data and smear critics.

But a successive series of investigations and inquiries since the emails were released in 2009 have exonerated the scientists. The final conclusion from the NSF's Office of Inspector General is no different [PDF; enter Case No. A09120086].

"No direct evidence has been presented that indicates the subject fabricated the raw data he used for his research or falsified his results," the report concludes. "Lacking any direct evidence of research misconduct, ... we are closing this investigation with no further action."

The NSF released its conclusions last week and, following standard protocol for investigations, did not mention Mann by name. "We do not identify the subject by name due to privacy considerations," said Susan Carnohan, chief of staff to the inspector general.

Mann, in an interview, said he had received a letter from the inspector general about the case that referenced the same case number identified in the NSF's closeout memorandum.

The number of deaths attributed to natural hazards in the U.S. has declined, even as the costs of major disasters like tornadoes are on the rise. Insurance industry analysts say that tornadoes, severe thunderstorms, and related weather events have caused nearly 57 percent of all insured catastrophe losses in the United States since 1953. According to analysts, losses of $1 billion or more from a single tornado are becoming more frequent.

The monster tornado in Joplin, Mo., last month killed more than 150 people and damages could reach as high as $3 billion. 

According to the National Science and Technology Council, “Americans today are more vulnerable than ever to severe weather events caused by tornadoes, hurricanes, severe storms, heat waves, and winter weather.”

Population changes, wealth distribution, construction of dense infrastructure in areas prone to severe weather have increased losses resulting from tornados and severe storms.

The population could be less vulnerable to the effects of severe weather if the federal government expanded funding for improved detection and warning systems, fostered efforts to build more resilient buildings and infrastructure, and financed research and development to better understand why and where severe thunderstorms and tornadoes occur.

Congress passed the National Windstorm Impact Reduction Act in 2004, which was aimed at reducing loss of life and property from tornados and severe thunderstorms, but it is unclear whether the program made progress toward its objective. Congress never approved a specific appropriation. The four agencies responsible for the program—the National Science Foundation, the National Institutes of Standards and Technology, NOAA, and the Federal Emergency Management Agency —did not identify a line item for the program in their annual budgets.