That's the point, 100 years is just a blip in earth's history. The climate has changed drastically up and down long before humans were on the scene. We are in a relative cooler period right now and a .5 C rise over 100 years is nothing to be alarmed about.
There have been periods where no ice existed at the poles and periods where ice covered most of the USA. Well before anyone know what fossil fuels were.
Remember when global warmists predicted 20 foot rise in sea levels? In the last 25 years as measured by NASA it's gone up 93 mm, about 3.6 inches.