The premier of Canada's British Columbia province wants to ban imports of U.S. thermal coal, and Justin Trudeau is "carefully and seriously" considering the idea as part of a retaliation for the U.S. tariff on Canadian lumber.

Quick fact: British Columbia exports 6.6 million metric tons of thermal coal a year, 94% of it from the U.S., and most of it to Asia, according to Bloomberg.

What that would mean: "Essentially, what this does is it wipes out the last remaining option for U.S. coal exporters to get their products off the northwest coast to Asia," Williams-Derry of the Sightline Institute.