Europe was already facing an energy crunch. Then President Trump spoke up about banning U.S. diesel exports, and the continent's problems got worse.

ICE gasoil futures, used as a benchmark for diesel in Europe, jumped as much as 7% today before giving up some of their gains, bringing their year-to-date gains to more than 135%. Trump said yesterday that he was open to an export ban-despite opposition from the U.S. oil industry, which stands to lose billions of dollars in revenue if it it can't ship diesel aboard.

The U.S. is the world's largest exporter of the fuel, accounting for about 20% of globally traded seaborne diesel.

"A full or partial US export ban would therefore hit a market that is already severely short of supplies from the Middle East and Russia," Danish commodity trading firm Global Risk Management said. "Europe is particularly exposed and would have to compete more aggressively for alternative cargoes."

If the U.S. implements a ban, it wouldn't be the first time Trump's policies have squeezed European energy consumers. The U.S. war with Iran choked off shipments of liquefied natural gas through the Strait of Hormuz, leaving Europe short of natural gas going into the winter heating season.