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Abstract

The Amazon forest is regarded as a tipping element of the Earth system, because of a potential large-scale regime change from tropical forest to woodland savanna and grassland, which could be triggered by anthropogenic land use and climate change. Recent conceptual and data-driven research focused on the hysteresis of such a regime change and found that fire could enhance the irreversibility of large-scale Amazon die-back. However, large-scale feedback analyses which integrate the interplay of fire with climate and land-use change are currently lacking. Here we apply the fire-enabled Earth system model CM2Mc-LPJmL to study such feedback mechanisms in the Amazon. We specifically test the role of fire for Amazon forest recovery under different atmospheric CO2 concentration levels (i.e. the magnitude of climate forcing) after complete deforestation. We find that fire prevents forests from regrowing on an area of 353-515 Mio ha (56-82 % of potential natural forest), depending on atmospheric CO2 concentration. Our simulation results show that fire is a major contributor to the irreversibility of a transition from forest to grassland by locking the Amazon in a stable grassland state. These findings emphasize the urgency of keeping deforestation and atmospheric CO2 concentrations within stable boundaries that would safeguard the Amazon forest.