If we continue along the business-as-usual fossil-fuel-use track, we run the risk, late in the twenty- first century, of triggering an abrupt reorganization of the ocean’s thermohaline circulation. This conclusion is based on evidence stored in Greenland ice, continental-margin sediments, and mountain moraines that tells us that the large and abrupt global climate changes during the last period of glaciation were associated with sudden reorganizations of the ocean’s thermohaline circulation and on simulations carried out in joint atmosphere-ocean models that suggest that raising the greenhouse capacity of the atmosphere to the carbon-dioxide equivalent of 750 ppm would cripple the ocean’s conveyor circulation. However, the recent discovery by Gerard Bond that the 1500-year cycle which paced these glacial disruptions continued in a muted form during times of interglaciation casts a new light on this situation. It leads me to suspect that the large and rapid atmospheric changes of glacial time were driven by a sea-ice amplifier. If so, then, because little sea ice will remain at the time of a greenhouse-induced thermohaline reorganization, perhaps the threat will be far smaller than I had previously envisioned.