When the weather turns cold and days get short, Annemarie O’Connell heads to the beach. Late on a December afternoon in 2025, she bundled up and drove to the shore in Truro, Mass. It’s near the tip of Cape Cod, a peninsula that sticks out into the Atlantic Ocean.
It was dark and chilly as O’Connell scanned the beach with a flashlight. She was looking for stranded sea turtles — ones too cold to swim.
Like other reptiles, most sea turtles don’t generate their own body heat. Instead, they seek out water with the right temp to stay comfortable. Ideally, that’s between about 17° to 29° Celsius (62° to 85° Fahrenheit).
As the ocean warms in summer, many turtles swim north, toward the Arctic, to stay in that just-right temp zone. Later, as the water cools in fall and winter, they’ll head back south, toward the tropics. (This is true for sea turtles in the northern hemisphere. Below the equator, turtles swim toward cooler Antarctic waters in the Southern Hemisphere summer.)
But if the water drops below 10 °C (50 °F) before they move on, these turtles will get to...
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