To put their probes into the Arctic Ice, researchers hitched a ride on a South Korean icebreaker. Courtesy of Craig M. Lee/University of Washington hide caption

itoggle caption Courtesy of Craig M. Lee/University of Washington

Icehotel is located 120 miles above the Arctic Circle. The temperature outside is well below zero, but inside the hotel — while still, of course, below freezing — it's much warmer, hovering in the low 20s. Ari Shapiro/NPR hide caption

itoggle caption Ari Shapiro/NPR

Pumpjacks at the Inglewood oil fields in California in March. Some of the most controversial methods of oil extraction, like fracking, oil sands production and Arctic drilling, are also expensive. That's made them less profitable as the price of oil continues to fall. Richard Vogel/AP hide caption

itoggle caption Richard Vogel/AP

The Erebus and the Terror among icebergs, as illustrated in The Polar World by G. Hartwig in 1874. Sir John Franklin, British naval officer and arctic explorer, commanded the 1845 expedition of the ships to search for the Northwest Passage. All members of the expedition perished. G. Hartwig/Universal History Archive/Getty Images hide caption

itoggle caption G. Hartwig/Universal History Archive/Getty Images

A scientist stands in front of an ice-rich permafrost exposure in the coastal zone of Herschel Island, Yukon Territory, Canada. Ice in the permafrost is melting, contributing to rapid erosion. Michael Fritz/Alfred Wegener Institute hide caption

itoggle caption Michael Fritz/Alfred Wegener Institute