Monsoon rainfall is a defining feature of the seasonality of Earth's hydrological cycle and its variability has profound impacts on society. Previous studies have focused on regional monsoon characteristics. Here we show that all northern hemisphere (NH) regional monsoons vary in a cohesive manner driven by El Niño-Southern Oscillation variability. In addition, the NH summer monsoon (NHSM) precipitation has increased steadily in concert with an amplified Hadley circulation. Such an enhanced NHSM produces a “wet-gets-wetter” and “dry-gets-drier” trend in total precipitation through monsoon-desert coupling. The changes in the NHSM are rooted in a differential global warming pattern characterized by two features: (a) increasing thermal contrast between the warm western and cool eastern Pacific, and (b) increasing land-ocean and inter-hemispheric thermal gradients. The former feature largely reflects natural variability, whilst the latter is likely due to anthropogenic forcing. The results provide a statistical perspective for assessing the IPCC AR5's decadal prediction program.