This June 2018 photo provided by Polar Bears International shows polar bear standing on sea ice north of Svalbard, Norway. Arctic sea ice — frozen ocean water — shrinks during the summer as it gets warmer, then forms again in the long winter. How much it shrinks is where global warming kicks in, scientists say. The more the sea ice shrinks in the summer, the thinner the ice is overall, because the ice is weaker first-year ice. (BJ Kirschhoffer/Polar Bears International via AP)
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