As commenter Mike Knapp noted on the blog, IHS-CERA published yesterday a report that heavily critiques the Howarth study. It also argues that the EPA 2010 revision of methane leakage data overstates significantly the rate of methane leakage. The EPA revised upward significantly its estimated rate of methane leakage.
But then Professor Horwath constructed an estimate of a methane leakage rate for his study that was even much greater than the upwardly revised EPA numbers.
IHS-CERA is one of America's top energy consulting firms and argues the leakage rates in the Howarth study would create fires and explosions were they in fact true. See http://www.ihs.com/info/en/a/mis-measuring-methane-report.aspx?fid=c27aa1fc7c25439383a3f56928.
Bit by bit the Howarth study is being consigned to the junk heap.