Highly coordinated observations and autonomous decision-making are needed to improve our ability to detect, monitor, and predict weather, climate, and the onset of certain natural hazards. The 'sensorweb' concept has been proposed as a potential solution to this requirement. This paper presents two candidate uses for the concept, describes its capabilities and unique architectural properties, and outlines challenges to overcome for successful development of a sensorweb architecture. The conclusion proposes that the primary challenge to implementation of sensorwebs - beyond the obvious technical obstacles - will be our ability to develop and execute a long-term strategy that provides for the deployment of a series of compatible missions that deliver the full promise of envisioned sensorweb capabilities.