Annex 5: Natural system impacts of overshoot pathways

•Executive Summary: This annex reviews the potential impacts of overshooting 1.5 °C on natural systems, with a particular focus on tipping points, high impact events and hysteresis in the climate and natural systems. It examines five parts of the Earth system: 1. Atmosphere: (i) changes in the West African and Indian monsoon; (ii) changes in the frequency and reversibility of extreme events (e.g. heatwaves, intense rainfall). 2. Ecosystems: (i) loss of boreal forests (fires and pests); (ii) loss of the Amazon and other Tropical Rainforests (fire and drought); (iii) greening of the Sahel; (iv) lock into dust-bowl conditions. 3. Biodiversity: (i) loss of biodiversity, including insects; (ii) changes in ranges, phenology, physiology and morphology of terrestrial and freshwater species. 4. Oceans and coastal regions: (i) collapse of the Atlantic Meridional Overturning Circulation (AMOC); (ii) cooling of the subpolar gyre; (iii) frequency and of intensity of ocean heatwaves; (iv) frequency and of intensity of ocean deoxygenation and hypoxic events; (v) change in the rate of ocean acidification; (vi) loss of coral reefs. 5. Cryosphere: committed loss to the ocean of the ice stored within (i) the Greenland Ice Sheet; (ii) Antarctic ice sheets; and (iii) mountain glaciers; (iv) loss of perennial Arctic Sea ice; (v) permafrost thaw.

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