Editing IPCC:AR6/SR15/TS (section)

=== Climate Change Risks for Natural and Human systems ===

==== Terrestrial and Wetland Ecosystems ====

'''Risks of local species losses and, consequently, risks of extinction are much less in a 1.5°C versus a 2°C warmer world (''high confidence'').''' The number of species projected to lose over half of their climatically determined geographic range at 2°C global warming (18% of insects, 16% of plants, 8% of vertebrates) is projected to be reduced to 6% of insects, 8% of plants and 4% of vertebrates at 1.5°C warming (''medium confidence''). Risks associated with other biodiversity-related factors, such as forest fires, extreme weather events, and the spread of invasive species, pests and diseases, would also be lower at 1.5°C than at 2°C of warming (''high confidence''), supporting a greater persistence of ecosystem services. {3.4.3, 3.5.2}

'''Constraining global warming to 1.5°C, rather than to 2°C and higher, is projected to have many benefits for terrestrial and wetland ecosystems and for the preservation of their services to humans (''high confidence'').''' Risks for natural and managed ecosystems are higher on drylands compared to humid lands. The global terrestrial land area projected to be affected by ecosystem transformations (13%, interquartile range 8–20%) at 2°C is approximately halved at 1.5°C global warming to 4% (interquartile range 2–7%) (''medium confidence''). Above 1.5°C, an expansion of desert terrain and vegetation would occur in the Mediterranean biome (''medium confidence''), causing changes unparalleled in the last 10,000 years (''medium confidence''). {3.3.2.2, 3.4.3.2, 3.4.3.5, 3.4.6.1, 3.5.5.10, Box 4.2}

'''Many impacts are projected to be larger at higher latitudes, owing to mean and cold-season warming rates above the global average (''medium confidence'').''' High-latitude tundra and boreal forest are particularly at risk, and woody shrubs are already encroaching into tundra (''high confidence'') and will proceed with further warming. Constraining warming to 1.5°C would prevent the thawing of an estimated permafrost area of 1.5 to 2.5 million km2over centuries compared to thawing under 2°C (''medium confidence''). {3.3.2, 3.4.3, 3.4.4}

==== Ocean Ecosystems ====

'''Ocean ecosystems are already experiencing large-scale changes, and critical thresholds are expected to be reached at 1.5°C and higher levels of global warming (''high confidence'').''' In the transition to 1.5°C of warming, changes to water temperatures are expected to drive some species (e.g., plankton, fish) to relocate to higher latitudes and cause novel ecosystems to assemble (''high confidence''). Other ecosystems (e.g., kelp forests, coral reefs) are relatively less able to move, however, and are projected to experience high rates of mortality and loss (''very high confidence''). For example, multiple lines of evidence indicate that the majority (70–90%) of warm water (tropical) coral reefs that exist today will disappear even if global warming is constrained to 1.5°C (''very high confidence''). {3.4.4, Box 3.4}

'''Current ecosystem services from the ocean are expected to be reduced at 1.5°C of global warming, with losses being even greater at 2°C of global warming (''high confidence'').''' The risks of declining ocean productivity, shifts of species to higher latitudes, damage to ecosystems (e.g., coral reefs, and mangroves, seagrass and other wetland ecosystems), loss of fisheries productivity (at low latitudes), and changes to ocean chemistry (e.g., acidification, hypoxia and dead zones) are projected to be substantially lower when global warming is limited to 1.5°C (''high confidence''). {3.4.4, Box 3.4}

==== Water Resources ====

'''The projected frequency and magnitude of floods and droughts in some regions are smaller under 1.5°C than under 2°C of warming (''medium confidence'').''' Human exposure to increased flooding is projected to be substantially lower at 1.5°C compared to 2°C of global warming, although projected changes create regionally differentiated risks (''medium confidence''). The differences in the risks among regions are strongly influenced by local socio-economic conditions (''medium confidence''). {3.3.4, 3.3.5, 3.4.2}

'''Risks of water scarcity are projected to be greater at 2°C than at 1.5°C of global warming in some regions (''medium confidence'').''' Depending on future socio-economic conditions, limiting global warming to 1.5°C, compared to 2°C, may reduce the proportion of the world population exposed to a climate change-induced increase in water stress by up to 50%, although there is considerable variability between regions (''medium confidence''). Regions with particularly large benefits could include the Mediterranean and the Caribbean (''medium confidence''). Socio-economic drivers, however, are expected to have a greater influence on these risks than the changes in climate (''medium confidence''). {3.3.5, 3.4.2, Box 3.5}

==== Land Use, Food Security and Food Production Systems ====

'''Limiting global warming to 1.5°C, compared with 2°C, is projected to result in smaller net reductions in yields of maize, rice, wheat, and potentially other cereal crops,''' particularly in sub-Saharan Africa, Southeast Asia, and Central and South America; and in the CO<sub>2</sub>-dependent nutritional quality of rice and wheat (''high confidence''). A loss of 7–10% of rangeland livestock globally is projected for approximately 2°C of warming, with considerable economic consequences for many communities and regions (''medium confidence''). {3.4.6, 3.6, Box 3.1, Cross-Chapter Box 6 in this chapter}

'''Reductions in projected food availability are larger at 2°C than at 1.5°C of global warming in the Sahel, southern Africa, the Mediterranean, central Europe and the Amazon (''medium confidence'').''' This suggests a transition from medium to high risk of regionally differentiated impacts on food security between 1.5°C and 2°C (''medium confidence''). Future economic and trade environments and their response to changing food availability (''medium confidence'') are important potential adaptation options for reducing hunger risk in low- and middle-income countries. {Cross-Chapter Box 6 in this chapter}

'''Fisheries and aquaculture are important to global food security but are already facing increasing risks from ocean warming and acidification''(medium confidence)''. These risks are projected to increase at 1.5°C of global warming and impact key organisms such as fin fish and bivalves (e.g., oysters), especially at low latitudes (''medium confidence'').''' Small-scale fisheries in tropical regions, which are very dependent on habitat provided by coastal ecosystems such as coral reefs, mangroves, seagrass and kelp forests, are expected to face growing risks at 1.5°C of warming because of loss of habitat (''medium confidence''). Risks of impacts and decreasing food security are projected to become greater as global warming reaches beyond 1.5°C and both ocean warming and acidification increase, with substantial losses likely for coastal livelihoods and industries (e.g., fisheries and aquaculture) (''medium to high confidence''). {3.4.4, 3.4.5, 3.4.6, Box 3.1, Box 3.4, Box 3.5, Cross-Chapter Box 6 in this chapter}

'''Land use and land-use change emerge as critical features of virtually all mitigation pathways that seek to limit global warming to 1.5°C (''high confidence'').''' Most least-cost mitigation pathways to limit peak or end-of-century warming to 1.5°C make use of carbon dioxide removal (CDR), predominantly employing significant levels of bioenergy with carbon capture and storage (BECCS) and/or afforestation and reforestation (AR) in their portfolio of mitigation measures (''high confidence''). {Cross-Chapter Box 7 in this chapter}

'''Large-scale deployment of BECCS and/or AR would have a far-reaching land and water footprint (''high confidence'').''' Whether this footprint would result in adverse impacts, for example on biodiversity or food production, depends on the existence and effectiveness of measures to conserve land carbon stocks, measures to limit agricultural expansion in order to protect natural ecosystems, and the potential to increase agricultural productivity (''medium agreement''). In addition, BECCS and/or AR would have substantial direct effects on regional climate through biophysical feedbacks, which are generally not included in Integrated Assessments Models (''high confidence''). {3.6.2, Cross-Chapter Boxes 7 and 8 in this chapter}

'''The impacts of large-scale CDR deployment could be greatly reduced if a wider portfolio of CDR options were deployed, if a holistic policy for sustainable land management were adopted, and if increased mitigation efforts were employed to strongly limit the demand for land, energy and material resources, including through lifestyle and dietary changes (''medium confidence'').''' In particular, reforestation could be associated with significant co-benefits if implemented in a manner than helps restore natural ecosystems (''high confidence''). {Cross-Chapter Box 7 in this chapter}

==== Human Health, Well-Being, Cities and Poverty ====

'''Any increase in global temperature (e.g., +0.5°C) is projected to affect human health, with primarily negative consequences (''high confidence'').''' Lower risks are projected at 1.5°C than at 2°C for heat-related morbidity and mortality (''very high confidence''), and for ozone-related mortality if emissions needed for ozone formation remain high (''high confidence''). Urban heat islands often amplify the impacts of heatwaves in cities (''high confidence''). Risks for some vector-borne diseases, such as malaria and dengue fever are projected to increase with warming from 1.5°C to 2°C, including potential shifts in their geographic range (''high confidence''). Overall for vector-borne diseases, whether projections are positive or negative depends on the disease, region and extent of change (''high confidence''). Lower risks of undernutrition are projected at 1.5°C than at 2°C (''medium confidence''). Incorporating estimates of adaptation into projections reduces the magnitude of risks (''high confidence''). {3.4.7, 3.4.7.1, 3.4.8, 3.5.5.8}

'''Global warming of 2°C is expected to pose greater risks to urban areas than global warming of 1.5°C (''medium confidence'').''' The extent of risk depends on human vulnerability and the effectiveness of adaptation for regions (coastal and non-coastal), informal settlements and infrastructure sectors (such as energy, water and transport) (''high confidence''). {3.4.5, 3.4.8}

'''Poverty and disadvantage have increased with recent warming (about 1°C) and are expected to increase for many populations as average global temperatures increase from 1°C to 1.5°C and higher (''medium confidence'').''' Outmigration in agricultural-dependent communities is positively and statistically significantly associated with global temperature (medium confidence). Our understanding of the links of 1.5°C and 2°C of global warming to human migration are limited and represent an important knowledge gap. {3.4.10, 3.4.11, 5.2.2, Table 3.5}

==== Key Economic Sectors and Services ====

'''Risks to global aggregated economic growth due to climate change impacts are projected to be lower at 1.5°C than at 2°C by the end of this century (''medium confidence'').''' {3.5.2, 3.5.3}

'''The largest reductions in economic growth at 2°C compared to 1.5°C of warming are projected for low- and middle-income countries and regions''' (the African continent, Southeast Asia, India, Brazil and Mexico) (''low to medium confidence''). Countries in the tropics and Southern Hemisphere subtropics are projected to experience the largest impacts on economic growth due to climate
change should global warming increase from 1.5°C to 2°C (''medium confidence''). {3.5}

'''Global warming has already affected tourism, with increased risks projected under 1.5°C of warming in specific geographic regions and for seasonal tourism including sun, beach and snow sports destinations (''very high confidence'').''' Risks will be lower for tourism markets that are less climate sensitive, such as gaming and large hotel-based activities (''high confidence''). Risks for coastal tourism, particularly in subtropical and tropical regions, will increase with temperature-related degradation (e.g., heat extremes, storms) or loss of beach and coral reef assets (''high confidence''). {3.3.6, 3.4.4.12, 3.4.9.1, Box 3.4}

==== Small Islands, and Coastal and Low-lying areas ====

'''Small islands are projected to experience multiple inter-related risks at 1.5°C of global warming that will increase with warming of 2°C and higher levels (''high confidence'').''' Climate hazards at 1.5°C are projected to be lower compared to those at 2°C (''high confidence''). Long-term risks of coastal flooding and impacts on populations, infrastructures and assets (''high confidence''), freshwater stress (''medium confidence''), and risks across marine ecosystems (''high confidence'') and critical sectors (''medium confidence'') are projected to increase at 1.5°C compared to present-day levels and increase further at 2°C, limiting adaptation opportunities and increasing loss and damage (''medium confidence''). Migration in small islands (internally and internationally) occurs for multiple reasons and purposes, mostly for better livelihood opportunities (''high confidence'') and increasingly owing to sea level rise (''medium confidence''). {3.3.2.2, 3.3.6–9, 3.4.3.2, 3.4.4.2, 3.4.4.5, 3.4.4.12, 3.4.5.3, 3.4.7.1, 3.4.9.1, 3.5.4.9,
Box 3.4, Box 3.5}

'''Impacts associated with sea level rise and changes to the salinity of coastal groundwater, increased flooding and damage to infrastructure, are projected to be critically important in vulnerable environments, such as small islands, low-lying coasts and deltas, at global warming of 1.5°C and 2°C (''high confidence'').''' Localized subsidence and changes to river discharge can potentially exacerbate these effects. Adaptation is already happening (''high confidence'') and will remain important over multi-centennial time scales. {3.4.5.3, 3.4.5.4, 3.4.5.7, 5.4.5.4, Box 3.5}

'''Existing and restored natural coastal ecosystems may be effective in reducing the adverse impacts of rising sea levels and intensifying storms by protecting coastal and deltaic regions (''medium confidence'').''' Natural sedimentation rates are expected to be able to offset the effect of rising sea levels, given the slower rates of sea level rise associated with 1.5°C of warming (''medium confidence''). Other feedbacks, such as landward migration of wetlands and the adaptation of infrastructure, remain important (''medium confidence''). {3.4.4.12, 3.4.5.4, 3.4.5.7}