The cyclical recurrence of interglacial and glacial periods (we're technically still in one of these) can theoretically be explained by cyclically evolving prop

The cyclical recurrence of interglacial and glacial periods (we're technically still in one of these) can theoretically be explained by cyclically evolving properties of the Earth's orbit around the sun such as the precession of the Earth's ratational axis (google Milankovitch cycles). This theory is consistent with the gradual cooling trend observed thus far into the Holocene epoch, and predicts it will continue for tens of thousands of years. The linked graph shows this very nicely. A sudden, full-blown glacial period would be far more disastrous for human civilization than significant global warming. The latter would submerge densely populated coastal areas and force humans to move to the new coastlines, but the overall capacity of the Earth to support life would increase, just as it did at the start of the Holocene. The former would result in a large reduction in the Earth's carrying capacity and global famine. Any change in the Earth's temperature is going to be disruptive to both human civilization and the existence of other species on Earth. We have reversed the effects of several thousand years of cooling in just a couple of centuries and, assuming we are able to continue extracting and burning hydrocarbons at an unabated pace indefinitely (dubious) we could significantly change the face of the world, but it will still support our civilization, just in a very changed state. Avoiding the pain of this change is ample incentive to curb the use of hydrocarbons. (Edit: It has taken centuries and a significant portion of the world's hydrocarbon reserves to produce less than a degree of warming. At this rate, even if we evaded peak-oil for another thousand years the Earth will still be in a glacial period.) However, we should be much more aware of events that could trigger another glacial period. Megaeruptions or large meteor impacts could plunge global temperatures suddenly and catastrophically. These are far greater threats to our species, but we are both incapable of adequately predicting them or preventing them if we do predict them. The probability of this sort of event happening in a single human lifespan is remote, while global warming is a certainty, but these events will eventually occur with certainty. Managing global warming is certainly a good idea for the comfort of our civilization, but we should have more eyes on the bigger threats. (Edit: Even if we tried, we would be unable to maintain global warming indefinitely simply by burning hydrocarbons. In the ten-thousand year time-frame we will need to find other ways to combat gradual cooling.)