Earth’s climate changes naturally due to changes in orbital relationships with the sun, configurations of continents and oceans, solar luminosity, naturally varying CO2 levels, volcanism, and internal atmosphere/ocean oscillations. Proxy geological and paleontological indicators suggest that past average surface temperatures have been as much as ~20 C higher than present, and 4-6 C colder than present during major glaciations. The history of natural change has led skeptics of anthropogenic warming to claim current warming is natural and caused by the sun and/or internal oscillations. But solar irradiance is declining and internal cycles have no net warming effect. Greenhouse warming theory, on the other hand, is corroborated by surface and atmospheric observations as well as modeling of atmospheric physics. As society shows no inclination toward seriously cutting emissions, warming will continue with momentous consequences for future generations. All that is known about natural and anthropogenic climate change is currently being applied to attribution studies that seek to estimate how much anthropogenic forcing has contributed to hurricanes and other weather-related events.