The Biosphere Under Potential Paris Outcomes

Rapid economic and population growth over the last centuries have started to push the Earth out of its Holocene state into the Anthropocene. In this new era, ecosystems across the globe face mounting dual pressure from human land use change (LUC) and climate change (CC). With the Paris Agreement, the international community has committed to holding global warming below 2°C above preindustrial levels, yet current pledges by countries to reduce greenhouse gas emissions appear insufficient to achieve that goal. At the same time, the sustainable development goals strive to reduce inequalities between countries and provide sufficient food, feed, and clean energy to a growing world population likely to reach more than 9 billion by 2050. Here, we present a macro‐scale analysis of the projected impacts of both CC and LUC on the terrestrial biosphere over the 21st century using the Representative Concentration Pathways (RCPs) to illustrate possible trajectories following the Paris Agreement. We find that CC may cause major impacts in landscapes covering between 16% and 65% of the global ice‐free land surface by the end of the century, depending on the success or failure of achieving the Paris goal. Accounting for LUC impacts in addition, this number increases to 38%–80%. Thus, CC will likely replace LUC as the major driver of ecosystem change unless global warming can be limited to well below 2°C. We also find a substantial risk that impacts of agricultural expansion may offset some of the benefits of ambitious climate protection for ecosystems. Plain Language Summary Ecosystems across the world are under increasing pressure from man‐made climate change and humanity's use of land for agriculture. While countries have agreed to limit climate change to less than 2 degrees in the 2015 Paris Agreement the success of climate protection is currently uncertain. At the same time, continued population growth is causing demand for food and bioenergy to rise. We use computer simulations to explore which ecosystems are at risk of major change due to climate change and land use by the end of the 21st century. We find that climate change could transform between 16% and 65% of all ecosystems worldwide substantially, depending on how successful greenhouse gas emissions can be reduced. 11% to 25% of ecosystems may also experience severe impacts from land use, depending on how much land is needed for agriculture. In the worst case we studied, climate change and land use change risk