Koonin mentions that this climate is always changing. This is a standard line in the  because it sounds reasonable at first blush, but of course it conveys a deep falsehood. The fact is that the actual peer-reviewed scientific research shows that (a) the rate of warming over the past century is unprecedented as far back as the 20,000 years paleoclimate scientists are able to extend the record and (b) that warming can  be explained by human influences Indeed, it is the  of warming that presents such risk to human civilization and our environment. There is no doubt that there were geological periods that were warmer than today due to long-term changes in greenhouse gas concentrations driven by natural factors like plate tectonics. But consider the early Cretaceous 100 million years ago when  concentrations were even higher than today, and there were dinosaurs roaming the ice-free poles. Over the last 100 million years, nature slowly buried all of that additional  beneath Earth’s surface in the form of fossil fuels. We are now unburying that carbon a ** times faster than it was buried, leading to unprecedented rates of increase in greenhouse concentrations and resulting climate changes. To claim that this is just part of a natural cycle is to be either deeply naive or disingenuous.