The methane routinely released by container and cruise ships operating on liquefied natural gas (LNG) makes them a bigger climate threat than the heavy fuel oil vessels they’re increasingly replacing, according to a bombshell working paper released yesterday by the International Council on Clean Transportation and STAND.earth.

The report concludes that the most popular among the new generation of LNG Marine engines “is also the leakiest,” ICCT reports, producing 70 to 82% more carbon and methane pollution than the least-polluting traditional fuel. While LNG produces fewer immediate emissions than the alternatives when it’s burned onboard a ship, its impact is multiplied when a life cycle analysis factors in the methane released through hydraulic fracturing, or fracking, as well as “methane slip” during routine ship operations