Having dominated pipeline natural gas supplies to Europe for decades, it’s taken Russia less than a year to become one of the region’s biggest sources of tanker-borne fuel.

That’s thanks to Yamal LNG, which last December started chilling gas into liquid in harsh Arctic conditions—a rare case of a production plant starting ahead of schedule. While market forces explain why so much of Yamal’s supply is ending up in Europe, instead of its main intended markets in Asia, the development...