Researchers from the University of Copenhagen have traced when polar bear numbers in the Arctic began to dwindle as climate change warmed the oceans. The findings show that rising sea temperatures started influencing the lives of Arctic predators around 20,000 years ago. The study appears in Science Developments.
According to the lead author, Michael Westbury, the drop in polar bear populations is linked to higher sea temperatures. Warmer waters reduce sea ice, which means fewer seals for polar bears to hunt.
To reconstruct the bears’ history, scientists relied on two independent data sets and methods to estimate historical population sizes and the animals’ genetic diversity over the last twenty thousand years.
What surprised researchers most was the outsized effect of even modest environmental shifts. Studies indicate that water temperatures around Greenland rose by about 0.2–0.5 °C over the past 20,000 years, contributing to a 20–40% decline in the polar bear population.
Looking ahead, the team notes that Greenland’s seas could warm by 2–5 °C. That change would be roughly ten times larger than what occurred over the last 20 millennia, signaling serious challenges for polar bears, which sit at the top of the Arctic food chain. Polar bears influence entire Arctic ecosystems, and shifts in their numbers ripple through the region’s balance of species. (Attribution: Science Developments)
Earlier analyses suggested polar bears sought refuge in Siberia during prior periods of global warming, highlighting the species’ long history of responding to climate-driven habitat changes. (Attribution: Science Developments)