No, the climate has always changed. That's what it does. and the ultimate source of almost all heat on Earth's surface is the Sun. This is mitigated primarily by solar cycles, orbital cycles, and yes gas composition. BUT over 95% of the greenhouse gas effect is controlled by WATER VAPOR, which mankind has almost no appreciable effect on. CO2, the boogieman of Chicken Little alarmists and ManBearPigs only makes up 0.03% of our atmosphere.