A window into the future of the Earth, hidden in the jungles of Costa Rica's volcanoes

The CO2 fertilization response of the terrestrial biosphere contributes among the largest sensitivities and uncertainties across projections of the Earth's future. The source of that uncertainty can be pinpointed to the largest fluxes in the biosphere: the tropics. Free Air CO2 Enrichment (FACE) experiments have contributed immensely to our understanding of short-term CO2 fertilization, but, outside of a small pilot study in development, have been absent in the tropics. This is largely due to numerous hurdles of not only conducting such experiments in challenging environments, but also due to the need to expand their extent considerably to encompass the enormous diversity of species-level responses, in addition to the need for multi-decadal scale responses. As such, we have remained at a critical impasse in our ability to advance understanding of the response of the tropical biosphere to increasing CO2. Recent discoveries have found a cluster of volcanoes degassing CO2 into tropical ecosystems in Costa Rica at concentrations similar to future Earth atmosphere levels. The degassing has been occurring persistently from 10s to 100s of years over 10s to 100s of square kilometers, at different levels depending on the volcano. Fortuitously, this provides a natural "experiment" across a range of conditions needed to assess a widespread and long-lived tropical ecosystem response to elevated CO2: tree species will have had time to shift in composition, traits, structure, and function. Nonetheless, due both to the challenges with assessing these changes on the ground, and heterogeneity causing problems with coarse-scale satellite remote sensing observations, this "window" into the future of the Earth has remained veiled. Here, we describe an airborne-based plan designed to uncover this gem hidden in the jungles of Costa Rica's volcanoes.