Future space observing systems for the world climate research programme

Even if current initiatives such as TOGA (Tropical Ocean Global Atmosphere) or WOCE (World Ocean Circulation Experiment) are completely successful in attaining their objectives, a major challenge will remain, namely to balance the global energy and water cycles. Recognising the need to redress this gap in knowledge, a new initiative has been formulated within the framework of the World Climate Research Programme. This is GEWEX, the Global Energy Water Cycle Experiment, which is intended to address this challenge through the combination of new observing systems (also existing operational ones) and global atmosphere-ocean-land-ice models. The aim will be to exploit technological advances expected to happen with the advent of the space station era coupled with the introduction of ever more powerful computers. This paper outlines the objectives of GEWEX and its demands for space-borne instrumentation accepting that meeting them will set the pattern of future observing systems for the World Climate Research Programme.