Tropical forests release more carbon dioxide to the atmosphere than they remove from it, according to a new study, finding that most of the release is due to deforestation and degradation. Studies to determine the global carbon contribution of the tropics have yielded vastly different results, with some suggesting that these forests act as an overall carbon sink and others suggesting they are a modest net source. The answer is critical for understanding climate science and informing climate change mitigation policies. In their analysis, Alessandro Baccini et al. analyzed the carbon density of woody live vegetation across tropical America, Africa, and Asia for the period 2003 to 2014. They combined a comprehensive array of data, including carbon estimates from NASA, satellite imagery and field measurements. They report that carbon losses exceed gains on every continent, with the greatest losses, 60%, occuring in the American tropics. However, the vast majority of the land area across all the tropics exhibited no significant change in carbon over the 12-year period of study, with only 15% of the total area experiencing losses and only 6% experiencing gains. For the carbon loss that did occur, the majority was due to deforestation and degradation, particularly in tropical America and Africa. Remarkably, the authors found trends between local policies and carbon abundance; for example in Brazil, decreasing losses in carbon density are evident during the early period of the study, which the authors attribute to retractions in soy and cattle production, increases in monitoring and enforcement together with fines and embargos on illegal deforestation, and the creation of new protected areas.