Quite likely, European expansion in the Americas played a role. With perhaps 90 per cent of the indigenous population eliminated by the effects of conquest and infectious disease, forests reclaimed regions in which terraced agriculture and irrigation had been practised for centuries. In Mesoamerica, Amazonia and the Andes, some 50 million hectares of cultivated land may have reverted to wilderness. Carbon uptake from vegetation increased on a scale sufficient to change the Earth System and bring about a human-driven phase of global cooling.12
