Abstract Sea level is an important—perhaps the most important—master variable of the marine Stratigraphic record. Whether we study facies distribution, climatic indices, or biogeography through time, we usually invoke sea level changes as part of the physical explanation for the observed variations. For many purposes we can consider the sediment-producing machine of erosion, transport, and accumulation, as a system driven by sea level fluctuations. Feedback mechanisms are part of this system. Negative feedback tends to slow down sea level changes, once it has started, and positive feedback tends to accelerate them. Positive feedback is of great interest, because it can produce run-away situations accompanied by rapid change and resulting in extreme conditions. Global reduction of sensitive organisms, and extinctions, may result from such run-away phenomena. I will consider three types of positive feedback (Figure 1): albedo feedback, greenhouse feedback, and feedback from collapse of transient reservoirs.