Melting arctic sea ice isn’t just threatening polar bears’ lives—it’s threatening their gene pool. The loss of ice means more contact between polar bears and genetically-similar grizzlies, which means cross-breeding, scientists say. Hunters have shot at least two polar-grizzly crosses since 2006, the Independent reports. Other species appear to be mixing, too, including beluga whales and narwhals, as well as bowhead and right whales.
One study found 22 sets of populations that could intermix. And “not all cross-species matings will produce viable, or indeed any, offspring,” notes an expert. Another example of the dangers involved: polar-grizzly mixes have trouble swimming, essential to their search for food. But things could turn around for polar bears, another study finds, if we make major cuts to greenhouse gases in the next 10 years.