Some are, yes. There are natural fluctuations in CO2 content and temperature and these are seen as a jagged line graphs of these measurements. These fluctuations are a result of many natural factors including seasons, sunspot cycles etc.
However, also obvious on these graphs is constant upward averagetemperature. This is not from natural causes. It is faster than anything that has occurred in since humans first appeared on the planet. This is a result of additional heat being held in the atmosphere due to the rapid emitting of greenhouse gases – primarily CO2.