"LAGO DE SAN IGNACIO, Baja California - The season of migration has come again to the warm blue waters off the coast of Mexico. Mother gray whales are nursing their newborn calves, plumping them up for the 6,000-mile trip next month to summer feeding grounds in the Arctic.
This migration, one of the longest of any of the world's wild mammals, has gone on for thousands of years. Increasingly, the watery voyage raises questions about how the changing climate is affecting species that live in the Arctic, the part of the world transforming most dramatically from humanity's greenhouse gas emissions.
As ocean and atmospheric temperatures rise, the gray whales -- and other Arctic dwellers like the walrus, polar bear, ice seal and Arctic fox -- are making their way in an unknown warming world. Their habitat and food supply are shifting as a result of warmer waters and shrinking sea ice."