The ice core studies show that CO2 levels had not exceeded ____ for 800,000 years, but most recently CO2 levels are _____, which is an increase of ____. 300 ppm, 411 ppm, 45% 411 ppm, 300 ppm, 45% 300 ppm, 280 ppm, 10% 170 ppm, 411 ppm, 142%