For Europe’s environment and energy future, the 2019 wild-card is Brexit, and how the U.K.'s split from the European Union could change the continent’s equation on everything from greenhouse gases to pesticides. Here are key elements on different parts of the continent:

U.K.

British lawmakers will vote by Jan. 17 on the U.K.’s divorce deal with the EU. If approved, chemical companies will be able to trade freely across the bloc while energy and manufacturing companies will continue to follow...