Deforestation is one of the most significant environmental challenges faced by the world today, particularly because of its direct and indirect impacts on ecosystems, human livelihoods, and global climate. From the perspective of ecological economics, deforestation is not merely a loss of trees; it represents a complex interaction of market and non-market costs, where traditional economic measures often fail to capture the true value of ecological services lost. One of the central concepts in ecological economics is the idea of marginal external cost (MEC), which refers to the additional cost imposed on society or the environment by an incremental unit of an economic activity, in this case, deforestation. Unlike private costs borne by the landowner or timber company, marginal external costs are not reflected in market prices and include factors such as carbon emissions, biodiversity loss, soil degradation, and disruption of hydrological cycles. To illustrate the marginal external cost of deforestation, it is useful to consider the case study of the Amazon Rainforest in Brazil. The Amazon is often referred to as the "lungs of the planet," producing around 20% of the world’s oxygen and acting as a significant carbon sink. In recent decades, extensive deforestation in the Brazilian Amazon has been driven primarily by logging, cattle ranching, and agricultural expansion. According to ecological economics, each additional hectare of forest cleared imposes incremental environmental costs that are rarely accounted for in market transactions. For instance, when a hectare of rainforest is cleared for soy cultivation, the private benefits, such as profits from crop sales, are easily measured. However, the marginal external costs—ranging from increased greenhouse gas emissions to the loss of habitats for countless species—remain externalized. One of the most quantifiable marginal external costs of deforestation in the Amazon is carbon emissions. Tropical forests store vast amounts of carbon both in their biomass and soil. When trees are cut and burned, significant quantities of carbon dioxide are released into the atmosphere, contributing to global climate change. In ecological economic terms, the marginal external cost of deforesting one hectare can be estimated by the additional social cost of carbon released. Studies have suggested that a single hectare of tropical forest can release between 100 to 200 metric tons of CO₂ when