Today's climate change is indeed caused by humans. The scientific understanding of it is nearly as good as our understanding of gravity. If you hold a ball in your hand and let it go, you can bet it will move downward. Similarly, if you add carbon dioxide to the atmosphere by burning fossil fuels, Earth's temperature will increase. The ongoing, abrupt increase in Earth's temperature differs markedly from the much slower increases caused by natural effects. People who purport to explain climate change as a natural climate variation are imposing their ignorance onto the public.