The authors highlight the strategic role of technological spillovers—the fact that extraction becomes cheaper as more countries exploit the Arctic— in leaving Arctic fossil fuels untouched. To avoid an “Arctic snowball effect”, greener countries with access to the Arctic should coordinate on not exploiting the Arctic, which will keep barriers to entry high enough to discourage less environmentally concerned countries from entering. Calibration suggests Norway, or prospects of a future green U.S., could be pivotal. Canada also has an important role to play.