Abstract. Monsoon has earned increasing attention from the climate community since the last century, yet only recently regional monsoons have been recognized as a global system. It remains a debated issue, however, as to what extent and at which time scales the global monsoon can be viewed as a major mode of climate variability. For this purpose a PAGES Working Group (WG) was set up to investigate the concept of the global monsoon and its future research directions. The WG's synthesis is presented here. On the basis of observation and proxy data, the WG found that the regional monsoons can vary coherently, although not perfectly, at various time scales, ranging from interannual, interdecadal, centennial and millennial, up to orbital and tectonics time scales, conforming the global monsoon concept across time scales. Within the global monsoon system each subsystem has its own features depending on its geographic and topographic conditions. Discrimination of global and regional components in the monsoon system is a key to reveal the driving factors of monsoon variations, hence the global monsoon concept helps to enhance our understanding and to improve future projection of the regional monsoons. This paper starts with a historical review of the global monsoon concept in both modern and paleo-climatology, and an assessment of monsoon proxies used in regional and global scales. The main body of the paper is devoted to a summary of observation data at various time scales, providing evidence for the coherent global monsoon system. The paper concludes with a projection of future monsoon shifts into a warming world. The synthesis will be followed by a companying paper to discuss driving mechanisms and outstanding issues in the global monsoon studies.
