Ecologists and Earth system scientists are collecting vast amounts of data related to the global carbon and water cycles. One of the grand challenges facing our field is how to effectively utilize the wealth of observations in order to improve our theoretical understanding and generate policy-actionable projections of ecosystem responses to change. The overall theme of this talk is to address how we can harness the accumulating ecological data from studies around the world, in combination with advanced modeling techniques, to improve our understanding of the causes and consequences of long-term changes in global ecosystem function and the terrestrial carbon cycle. My work uses process-based modeling, model-data fusion, and data-mining tools to do so. The results highlight key knowledge gaps, identify the most pressing data needs, and advance our understanding of the response of the biosphere to global change.