Like the canary in the coal mine, animals have long been recognized as sentinels or early warning systems for changing environmental conditions that may also impact human health. Even within the animal kingdom, key sentinel species and vulnerable communities have been identified that are more susceptible to changing environments and thus act as bioindicators of emerging health threats. Along coastal ecosystems around the world, an increasing and alarming number of wildlife dieoffs have been reported in recent years, attributed in part to a combination of changing water temperatures, algal bloom effects, and shifting prey availability. In addition to these environmental shifts associated with climate change, direct anthropogenic influences such as overfishing and pollution are contributing to wildlife morbidity and mortality in coastal ecosystems. This increasing number of wildlife dieoff events are a harbinger of planetary systems being out of balance, and the short-term view that human civilization has taken in harvesting natural resources without a long-term sustainability vision will have to change if we are to survive and thrive in the coming decades. From a global perspective, key human communities can also be identified that act as sentinels of planetary health, as they experience the pressures of growing population trajectories and resource demands amidst harsh environments and living conditions. These ‘on the edge’ communities may not have the resilience to bounce back after repeated extreme weather events that have a cascade of effects on health, food, and water systems. Finally, even within environmental systems, some such as corals are particularly vulnerable and act as sentinels of ecosystem change. Taken together, the animal, human, and ecosystem sentinels are a powerful early warning system that can guide and inform on priorities and solutions to help stabilize planetary systems and create a more resilient, sustainable global civilization.