"The Holocene record of atmospheric CO2 and methane concentrations is an enigma. Concentrations of both gases increased from the beginning of the epoch 11,700 years ago to about 10,000 BP, then declined for several thousand years, but by 6000 BP, concentrations of both gases were steadily increasing again. This mid-late Holocene rise in greenhouse gases is unusual; similar patterns are not observed during previous interglacials. While various mechanisms have been proposed to explain these changes in Holocene CO2 and methane, there is one undisputed feature of this epoch that we know is different from the rest of Earth history: the existence of behaviorally modern humans. How humanity could have influenced the Holocene increase in CO2 and methane concentrations is the subject of the COEVOLVE project.In an interdisciplinary study that combines the social and natural sciences, we will reconstruct anthropogenic CO2 and methane emissions over the Holocene using a state-of-the-art model of terrestrial biogeochemistry and earth surface processes. The novelty of our approach is to develop a geodatabase of anthropogenic activities derived from historical and archaeological observations to drive our model, and to evaluate our simulations against a new, comprehensive global reconstruction of past land cover. COEVOLVE is organized around three activities: 1) synthesis of observations of past land cover change from paleoecological archives, 2) development of a spatial database of the spread of technology, industry, culture, and trade that influenced global land use and resource consumption patterns and 3) informed by parts 1 and 2, modeling of terrestrial biogeochemical cycles and land surface processes including deforestation, soil erosion, and fire. With a new perspective on preindustrial environmental impact, the COEVOLVE project will make a breakthrough in our understanding of the influence of humans on greenhouse gas concentrations and global climate during the Holocene."