"Since the widespread combustion of fossil fuels, we have put a human fingerprint on atmospheric carbon dioxide," Joseph Bump, a forest science researcher at Michigan Technological University, said in a release. "That fingerprint shows up in trees, and it shows up in animals that eat trees, but it shows up with the least variation in the top predators."

Bump and his colleagues studied moose and wolf bone samples dating back to 1958 from Isle Royale National Park in Lake Superior. They also looked at 30,000-year-old bones from extinct dire wolves and prehistoric bison pulled from the La Brea tar pits in Los Angeles. They found the wolves provide a clearer record of environmental change than the plants, the moose or the bison.

The findings were published in the Proceedings of the Royal Society B.