The human climate: towards an Earth system-based perspective on human climate adaptation

The way life on Earth adapts to the climate can change the climate. In the Anthropocene, humans have become a planetary force dominating the biosphere. Could human climate adaptation therefore have substantial feedback effects on the Earth system? We work out the bio-geo-physical mechanisms of adaptation within a new Earth system-based framework of human climate adaptation. Thereby we can for the first time approximate the contribution of climate adaptation to the current state of affected planetary boundaries. By establishing what we call artificial climate niches, Homo sapiens is the only known species able to fully emulate all recorded climates on Earth at a small scale. Many of those niches exceed the human scale by orders of magnitude but still remain small at Earth system scales. Yet climate adaptation-Earth system-feedbacks are extremely disproportional to scale. Linking research from various domains, we find that human climate adaptation currently contributes ≥25.7 percent of annual greenhouse gas emissions and ≥73.2 percent of human freshwater withdrawals. Climate adaptation even affects the stratosphere: the ozone hole is largely a product of climate adaptation. The large majority of those impacts likely still results from adaptation to mostly stable Holocene climates and not yet from adaptation to climate change. This proves both the importance and the urgency of establishing a safe and just operating space for human climate adaptation.