[en] Even after extensive re-working of past data, in many instances we are incapable of resolving important aspects concerning climate change and variability including greenhouse gases such as CO₂, and aerosols. Virtually every monitoring system and data set requires better data quality, continuity, and homogeneity if we expect to conclusively answer questions of interest to both scientists and policy-makers. This is a result of the fact that long-term meteorological data, (both satellite and conventional) both now and in the past, are and have been collected primarily for weather prediction, and only in some cases, to describe the current climate. Long-term climate monitoring, capable of resolving decade-to-century scale changes in climate, requires different strategies of operation. Furthermore, the continued degradation of conventional surface-based observing systems in many countries (both developed and developing) is an ominous sign with respect to sustaining present capabilities into the future. Satellite-based observing platforms alone will not, and cannot, provide all the necessary measurements. Moreover, it is clear that for satellite measurements to be useful in long-term climate monitoring much wise implementation and monitoring practices must be undertaken to avoid problems of data inhomogeneity that currently plague space-based measurements. Continued investment in data analyses to minimize time-varying biases and other data quality problems from historical data are essential if we are to adequately understanding climate change, but they will never replace foresight with respect to ongoing and planned observing systems required for climate monitoring. Fortunately, serious planning for a Global Climate Observing System (GCOS) is now underway that provides an opportunity to rectify the current crisis. 76 refs., 22 figs