Editing IPCC:AR6/SR15/Chapter-3 (section)

=== 3.4.12 Summary of Projected Risks at 1.5°C and 2°C of Global Warming ===

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The information presented in Section 3.4 is summarised below in Table 3.5, which illustrates the growing evidence of increasing risks across a broad range of natural and human systems at 1.5°C and 2°C of global warming.

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'''Table 3.5'''

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'''Summary of projected risks to natural and human systems at 1.5°C and 2°C of global warming, and of the potential to adapt to these risks'''

Table summarizes the chapter text and with references supporting table entries found in the main chapter text. Risk magnitude is provided either as assessed levels of risk (very high: vh, high: h, medium: m, or low: l) or as quantitative examples of risk levels taken from the literature. Further compilations of quantified levels of risk taken from the literature may be found Tables 3.SM1-5 in the Supplementary Material. Similarly, potential to adapt is assessed from the literature by expert judgement as either high (h), medium (m), or low (l). Confidence in each assessed level/quantification of risk, or in each assessed adaptation potential, is indicated as very high (VH), high (H), medium (M), or low (L). Note that the use of l, m, h and vh here is distinct from the use of L, M, H and VH in Figures 3.18, 3.20 and 3.21.

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{| class="wikitable"
|-
! Sector
! Physical climate change drivers
! Nature of risk
! Global risks at 1.5°C of global warming above pre-industrial
! Global risks at 2°C of global warming above pre-industrial
! Change in risk when moving from 1.5°C to 2°C of warming
! Confidence in risk statements
! Regions where risks are particularly high with 2°C of global warming
! Regions where the change in risk when moving from 1.5°C to 2°C are particularly high
! Regions with little or no information
! RFC*
! Adaptation potential at 1.5°C
! Adaptation potential at 2°C
! Confidence in assigning adaptation potential
|-
| rowspan="3"| Freshwater
| rowspan="3"| Precipitation, temperature, snowmelt
| Water Stress
| Around half compared to the risks at 2°C <sup>1</sup>
| Additional 8% of the world population in 2000 exposed to new or aggravated water scarcity <sup>1</sup>
| Up to 100% increase
| M
|
| Europe, Australia, southern Africa
|
| 3
| l
| M
|-
| Fluvial flood
| 100% increase in the population affected compared to the impact simulated over the baseline period 1976–2005 <sup>2</sup>
| 170% increase in the population affected compared to the impact simulated over the baseline period 1976–2005 <sup>2</sup>
| 70% increase
| M
| USA, Asia, Europe
|
| Africa,<br />
Oceania
| 2
| l/m
| M
|-
| Drought
| 350.2 ± 158.8 million, changes in urban population exposure to severe drought at the globe scale <sup>3</sup>
| 410.7 ± 213.5 million, changes in urban population exposure to severe drought at the globe scale <sup>3</sup>
| 60.5 ± 84.1 million (±84.1 based on the SSP1 scenario)<br />
(based on PDSI estimate)
| M
| Central Europe, southern Europe, Mediterranean, West Africa, East and West Asia, Southeast Asia (based on PDSI estimate#)
|
| 2
| l/m
| L
|-
| rowspan="4"| Terrestrial ecosystems
| rowspan="3"| Temperature, precipitation
| Species range loss
| 6% insects, 4% vertebrates, 8% plants, lose &gt;50% range <sup>4</sup>
| 18% insects, 8% vertebrates, 16% plants lose &gt;50% range <sup>4</sup>
| Double or triple
| M
|
| Amazon, Europe, southern Africa
|
| 1,4
| m
| l
| H
|-
| Loss of ecosystem functioning and services
| m
| h
|
| M
|
| 4
|
|-
| Shifts of biomes (major ecosystem types)
| About 7% transformed <sup>5</sup>
| 13% (range 8–20%) transformed <sup>5</sup>
| About double
| M
|
| Arctic, Tibet, Himalayas, South Africa, Australia
|
| 4
|
|-
| Heat and cold stress, warming, precipitation drought
| Wildfire
| h
| Increased risk
| M
| Canada, USA and Mediterranean
| Mediterranean
| Central and South America, Australia, Russia, China, Africa
| 1, 2,<br />
4, 5
| l
| M
|-
| rowspan="15"| Ocean
| rowspan="6"| Warming and stratification of the surface ocean
| Loss of framework species (coral reefs)
| vh
| Greater rate of loss: from 70–90% loss at 1.5°C to 99% loss at 2°C and above
| H/very H
| Tropical/subtropical countries
| Southern Red Sea, Somalia, Yemen, deep water coral reefs
| 1,2
| h
| l
| H
|-
| Loss of framework species (seagrass)
| m
| h
| Increase in risk
| M
| Tropical/subtropical countries
| Southern Red Sea, Somalia, Yemen, Myanmar
| 1,2
| m
| l
| M/H
|-
| Loss of framework species (mangroves)
| m
| Uncertain and depends on other human activities
| M/H
| Tropical/subtropical countries
| Southern Red Sea, Somalia, Yemen, Myanmar
| 1,3
| m
| l
| L/M
|-
| Disruption of marine foodwebs
| h
| vh
| Large increase in risk
| M
| Global
| Deep sea
| 4
| m
| l
| M/H
|-
| Range migration of marine species and ecosystems
| m
| h
| Large increase in risk
| H
| Global
| Deep sea
| 1
| m
| l
| H
|-
| Loss of fin fish and fisheries
| h
| h/vh
| Large increase in risk
| H
| Global
| Deep sea, up-welling systems
| 4
| m
| m/l
| M/H
|-
| rowspan="3"| Ocean acidification and elevated sea temperatures
| Loss of coastal ecosystems and protection
| m
| h
| Increase in risk
| M
| Low-latitude tropical/subtropical countries
| Most regions – risks not well defined
| 1
| m
| m/l
| M
|-
| Loss of bivalves and bivalve fisheries
| m/h
| h/vh
| Large increase in risk
| H
| Temperate countries with upwelling
| Most regions – risks not well defined
| 4
| m/h
| l/m
| M/H
|-
| Changes to physiology and ecology of marine species
| l/m
| m
| Increase in risk
| H
| Global
| Most regions – risks not well defined
| 4
| l
| M/H
|-
| rowspan="2"| Reduced bulk ocean circulation and de-oxygenation
| Increased hypoxic dead zones
| l
| l/m
| Large increase in risk
| L/M
| Temperate countries with upwelling
| Deep sea
| 4
| m
| l
| M
|-
| Changes to upwelling productivity
| l
| m
| Increase in risk
| L/M
| Most upwelling regions
| Some upwelling systems
| 4
| l
| M
|-
| rowspan="2"| Intensified storms, precipitation plus sea level rise
| Loss of coastal ecosystems
| h
| h/vh
| Large increase in risk
| H
| Tropical/subtropical countries
|
| 1, 4
| m
| l
| M
|-
| Inundation and destruction of human/coastal infrastructure and livelihoods
| h
| h/vh
| Large increase in risk
| H
| Global
|
| 1, 5
| m/h
| m
| M/L
|-
| rowspan="2"| Loss of sea ice
| Loss of habitat
| h
| vh
| Large increase in risk
| H
| Polar regions
|
| 1
| l
| very l
| H
|-
| Increased<br />
productivity<br />
but changing fisheries
| l/m
| m/h
| Large increase in risk
| very H
| Polar regions
|
| 1, 4
| l
| m/l
| H
|-
| rowspan="3"| Coastal
| rowspan="3"| Sea level rise, increased storminess
| Area exposed (assuming no defences)
| 562–575th km <sup>2</sup> when 1.5°C first reached <sup>6,7,8</sup>
| 590–613th km <sup>2</sup> when 2°C first reached <sup>6,7,8</sup>
| Increasing; 25–38th km <sup>2</sup> when temperatures are first reached, 10–17th km <sup>2</sup> in 2100 increasing to 16–230th km <sup>2</sup> in 2300 <sup>6,7,8</sup>
| M/H (dependent on population datasets)
| Asia, small islands
| Small islands
| 2, 3
| m
| M
|-
| Population exposed (assuming no defences)
| 128–143 million when 1.5°C first reached
| 141–151 million when 2°C first reached
| Increasing; 8–13 million when temperatures are first reached, 0–6 million people in 2100, increasing to 35–95 million people in 2300 <sup>6</sup>
| M/H (dependent on population datasets)
| Asia, small islands
| Small islands
| 2, 3
| m
| M
|-
| People at risk accounting for defences (modelled in 1995)
| 2–28 million people yr <sup>–1</sup> if defences are not upgraded from the modelled 1995 baseline <sup>9</sup>
| 15–53 million people yr <sup>–1</sup> if defences are not upgraded from the modelled 1995 baseline <sup>9</sup>
| Increasing with time, but highly dependent on adaptation <sup>9</sup>
| M/H (dependent on adaptation)
| Asia, small islands, potentially African nations
| Asia, small islands
| Small islands
| 2, 3, 4
| m
| M
|-
| rowspan="2"| Food security and food production systems
| Heat and cold stress, warming, precipitation, drought
| Changes in ecosystem production
| m/h
| h
| Large increase
| M/H
| Global
| North America, Central and South America, Mediterranean basin, South Africa, Australia, Asia
|
| 2, 4, 5
| h
| m/h
| M/H
|-
| Heat and cold stress, warming, precipitation drought
| Shift and composition change of biomes (major ecosystem types)
| m/h
| h
| Moderate increase
| L/M
| Global
| Global, tropical areas, Mediterranean
| Africa, Asia
| 1, 2, 3, 4
| l/m
| l
| L/M
|-
| rowspan="4"| Human health
| rowspan="2"| Temperature
| Heat-related morbidity and mortality
| m
| m/h
| Risk increased
| VH
| All regions at risk
| All regions
| Africa
| 2, 3, 4
| h
| H
|-
| Occupational heat stress
| m
| m/h
| Risk increased
| M
| Tropical regions
| Africa
| 2, 3, 4
| h
| m
| M
|-
| Air quality
| Ozone-related mortality
| m (if precursor emissions remain the same)
| m/h (if precursor emissions remain the same)
| Risk increased
| H
| High income and emerging economies
| Africa, parts of Asia
| 2, 3, 4
| l
| M
|-
| Temperature, precipitation
| Undernutrition
| m
| m/h
| Risk increased
| H
| Low-income countries in Africa and Asia
| Small islands
| 2, 3, 4
| m
| l
| M
|-
| Key economic sectors
| Temperature
| Tourism (sun, beach, and snow sports)
| m/h
| h
| Risk increased
| VH
| Coastal tourism, particularly in subtropical and tropical regions
| Africa
| 1, 2, 3
| m
| l
| H
|}
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\*RFC: 1 = unique and threatened systems, 2 = extreme events, 3 = unequal distribution of impacts, 4 = global aggregate impacts (economic + biodiversity), 5 = large-scale singular events.

\# PDSI-based drought estimates tend to overestimate drought impacts (see Section 3.3.4); hence projections with other drought indices may differ. Further quantifications may be found in Table 3.SM.1

1 Gerten et al., 2013; 2 Alfieri et al., 2017; 3 Liu et al., 2018; 4 Warren et al., 2018a; 5 Warzawski et al., 2013; 6 Brown et al., 2018a; 7 Rasmussen et al., (2018); 8 Yokoki et al., (2018); 9 Nicholls et al., 2018 <sup>[[#fn:r1401|1401]]</sup>

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