Natural variations?

My next-door neighbor said that he now believes in global warming, but he thinks it's caused by natural cycles of the climate. He may be confusing climate trends with weather, which we all know from personal experience is highly variable and unpredictable. Natural variations in climate of course exist. The data shows that looking back 650,000 years, amounts of CO2 varried from 180 to 300 parts per million (ppm). Today's CO2 levels however, are around 380 ppm and rising. Check out Global Warming Myths and Facts.