Tariffs on Russian energy imports could provide the EU with a lever to reduce Russia's financial gains from its oil and gas exports and allow it to flexibly react to Moscow's actions in Ukraine, a team of economists from the European think tank Bruegel, Harvard, and the University of Cologne propose in a letter to Science and in a working paper. Among the authors is the University of Cologne's energy and market design expert Professor Dr. Axel Ockenfels.