Jet fuel shortages threaten to disrupt summer travel as the loss of supplies from the Middle East ripples across Asia and Europe. Exports from the Persian Gulf represented the largest single source of jet fuel supply to the global market before the U.S. and Israel attacked Iran on Feb. 28, according to the International Energy Agency . Iran's blockade of the Strait of Hormuz has cut off those jet fuel exports from the world. Europe is directly affected because the continent was the biggest importer of Middle Eastern fuel supplies. About 20% of the continent's jet fuel came from the Gulf, according to the IEA. The other major source of jet fuel exports to world markets are refineries in China, South Korea and India. But these refineries themselves rely heavily on crude oil from the Middle East. About 90% of the oil exported from the Gulf through the strait went to Asia before the war.…