No climatologist, indeed no scientist has ever said the Earth ever had a static climate, ever. I honestly don't know where you came up with that idea, please show me some sources, I want to read this for myself. What the climatologists do say, and have physical evidence of, going back hundreds of thousands of years through polar ice core samples (I know, that's still not as long as the age of the planet, but it is statistically way more significant than 100 years or so), is that since man entered the Industrial Age around the end of the 19th century, the climate has been changing at a faster rate than ever before, and by taking the amount of carbon dioxide that we have emitted into the atmosphere since the beginning of the Industrial Revolution out of computer simulations, the simulations can then directly account for the increase in the pace of climate change. In other words, yes human activity is directly responsible for the recent increase in climate change.