At a time of global changes, the world is striving to face and adapt to inevitable, possibly profound, alteration. Widening of droughts in southern Europe and sub-Saharan Africa, an increasing number of disasters, severe and more frequent flooding that could imperil low-lying islands and the crowded river deltas of southern Asia, are already taking place and climate change will cause additional environmental stresses and societal crises in regions already vulnerable to natural hazards, poverty and conflicts. A global multi-hazard early warning system is needed to inform us of pending threats. This report presents a state of the art assessment of existing monitoring/early warning systems (EWS) organized according to type of environmental threats , including air quality, wildland fires, nuclear and chemical accidents, geological hazards (earthquakes, tsunamis, volcanic eruptions, landslides), hydro-meteorological hazards (desertification, droughts, floods, impacts of climate variability, severe weather, storms, and tropical cyclones), epidemics and food insecurity. It identifies current gaps and needs with the goal of laying out guidelines for developing a global multi-hazard early warning system.