The position of the Arctic treeline has been associated with the preferred location of Arctic fronts that demarcate the boundary between Arctic and polar air masses. It has been argued that differences in summer energy balance, particularly in sensible heating, across treeline between forest and tundra may help determine the location of these frontal zones. Our observations of the energy balance at treeline show that the daily averaged summer heating contrast between treeline forest and tundra is an order of magnitude less than that previously proposed and that the influence on the atmosphere is confined to a shallow layer. In addition, maximum heating contrasts occurred in spring rather than in summer when the Arctic frontal zone is best expressed. Hence energy-balance contrasts at treeline are unlikely to be the major determinant of the position of the Arctic front. ¿ 2001 American Geophysical Union