The oceans play an important role in the geochemical cycle of methyl bromide (CH 3 Br), the major carrier of O 3 -destroying bromine to the stratosphere. Small temperature variations have large effects on the CH 3 Br concentration in seawater, and therefore on the exchange between the atmosphere and the ocean. The authors have quantified these effects using a simple steady state mass balance model. Modeling indicates that climate-induced CH 3 Br variations can be larger than those resulting from small (±25%) changes in the anthropogenic source, assuming that this source comprises less than half of all inputs.