The tropical carbon balance, heretofore mainly a sink, is now often reversing to become a source of carbon to the atmosphere in response to extreme events and trends in climate and land-use. Understanding long-term tropical carbon flux trends and the vulnerability of the tropical carbon sink to extreme events and climate change is of global importance and requires an improved understanding of heterogeneity in both patterns and processes. Critically, growing evidence shows divergent pathways for forests in the tropics in their recent carbon sink trends and sensitivity to extreme events. New investigations are needed to understand these processes and differences, interactions between the carbon cycle and diverse evolutionary histories, varying abiotic conditions and disturbance histories, unique human interactions, and distinct emergent ecosystem dynamics within and across tropical continents. In the process of scoping a pan-tropical NASA terrestrial ecology field campaign, we assessed the current state of knowledge on how climate and land-use change interact with the heterogeneous structure, function, and biodiversity of tropical forest biomes to affect the vulnerability of the current and future global carbon balance and how it feedbacks to influence people. Here, we report on key research needs that have been made urgently evident from the PANGEA scoping effort. Addressing these research needs requires an integrated program of field-based, airborne, and satellite data collection and modeling that spans the tremendous heterogeneity of tropical forests and provides an integrated understanding of diverse tropical ecosystems and their climate feedbacks.