International Polar Bear Day

What the day is

International Polar Bear Day is observed on February 27, organized by conservation groups and timed for the period when mothers and cubs are in their dens.

Origin and background

The bear is not white. Its guard hairs contain no white pigment and are essentially colorless and translucent, scattering light in a way that reads as white or cream against snow, and the skin underneath is black. A once-popular claim that the hairs act as fiber optics, piping sunlight down to warm that black skin, was tested and does not hold up; the hairs conduct light poorly and the idea has been abandoned.

The insulation is genuinely formidable, combining dense fur with a thick fat layer, and the practical consequence is that a polar bear's problem is frequently overheating rather than cold. They travel at a deliberate pace and can become heat-stressed when forced to run. It also means they are nearly invisible to thermal imaging, radiating so little heat that early aerial surveys using infrared largely failed to find them.

They are classified as marine mammals, which surprises people, because their life depends on the sea rather than the land. Sea ice is the platform from which they hunt seals, and seals are effectively their only high-energy food. When the ice retreats they are stranded ashore and fast, and the number of ice-free days is the variable that tracks body condition and cub survival. That is why this day is generally framed around emissions rather than around the bears directly.

They are also close enough to brown bears to interbreed, and hybrids have been confirmed in the wild, which points at a relatively recent divergence.

How to take part

• Turn the thermostat down a degree, which is the action the day's organizers actually ask for.
• Read about sea ice extent rather than about individual bears.
• Correct the fiber optic story, which is still widely repeated.
• Support research and monitoring, which is expensive and unglamorous.
• Look at an infrared image of a polar bear, which is a startling thing to see.