There is compelling evidence that the climate is changing. We can argue about the degree, nature and cause of the climate variations and whether there is in fact a change, but the only way to settle these arguments is with solid information. This requires improved global observations of the state variables and the forcings, the means to process these and understand them, and the ability to set them in a coherent physical (and chemical and biological) framework with models. Meanwhile, the information that helps settle these arguments and reduce uncertainties is also extremely valuable for many other practical applications for business, industry, government, and the general public. The implications are given for the climate observing system. Note the word "system" means a comprehensive approach that includes:

o Climate observations from both space-based and in situ platforms that are taken in ways that address climate needs and adhere to the ten principles outlined by the NRC (1999).

o A global telecommunications network and satellite data telemetry capacity to enable data and products to be disseminated.

o A climate observations analysis capability that produces global and regional analyses of various products for the atmosphere, oceans, land surface and hydrology, and the cryosphere.

o Four dimensional data assimilation capabilities that process the multivariate data in a physically consistent framework to enable production of the analyses, not just for the atmosphere but also for the oceans, land surface and so on.

o Global climate models that encompass all parts of the climate system and which are utilized in data assimilation and in making ensemble predictions.

o A climate observation oversight and monitoring center that tracks the performance of the observations, the gathering of the data, and the processing system.