Detailed measurements of atmospheric carbon dioxide (CO2) levels have been taken continuously for more than 50 years. The data show that CO2 levels have steadily increased every year. Today they are 25 percent higher than in 1957.
What's more, scientists have detailed records of past CO2 levels from ice core studies, which show that CO2 levels are higher today than at any point since our distant ancestors began migrating out of Africa 800,000 years ago.