Editing IPCC:AR6/SR15/Chapter-5 (section)

=== 5.2.3 Risks from 1.5°C versus 2°C Global Warming and the Sustainable Development Goals ===

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The risks that can be avoided by limiting global warming to 1.5ºC rather than 2°C have many complex implications for sustainable development (ICSU, 2017; Gomez-Echeverri, 2018) <sup>[[#fn:r40|40]]</sup> . There is ''high confidence'' that constraining warming to 1.5°C rather than 2°C would reduce risks for unique and threatened ecosystems, safeguarding the services they provide for livelihoods and sustainable development and making adaptation much easier (O’Neill et al., 2017b) <sup>[[#fn:r41|41]]</sup> , particularly in Central America, the Amazon, South Africa and Australia (Schleussner et al., 2016; O’Neill et al., 2017b; Reyer et al., 2017b; Bathiany et al., 2018) <sup>[[#fn:r42|42]]</sup> .

In places that already bear disproportionate economic and social challenges to their sustainable development, people will face lower risks at 1.5°C compared to 2°C. These include North Africa and the Levant (less water scarcity), West Africa (less crop loss), South America and Southeast Asia (less intense heat), and many other coastal nations and island states (lower sea level rise, less coral reef loss) (Schleussner et al., 2016; Betts et al., 2018) <sup>[[#fn:r43|43]]</sup> . The risks for food, water and ecosystems, particularly in subtropical regions such as Central America and countries such as South Africa and Australia, are expected to be lower at 1.5°C than at 2°C warming (Schleussner et al., 2016) <sup>[[#fn:r44|44]]</sup> . Fewer people would be exposed to droughts and heat waves and the associated health impacts in countries such as Australia and India (King et al., 2017; Mishra et al., 2017) <sup>[[#fn:r45|45]]</sup> .

Limiting warming to 1.5°C would make it markedly easier to achieve the SDGs for poverty eradication, water access, safe cities, food security, healthy lives and inclusive economic growth, and would help to protect terrestrial ecosystems and biodiversity ( ''medium evidence, high agreement)'' (Table 5.2 available at the end of the chapter). For example, limiting species loss and expanding climate refugia will make it easier to achieve SDG 15 (see Chapter 3, Section 3.4.3). One indication of how lower temperatures benefit the SDGs is to compare the impacts of Representative Concentration Pathway (RCP) 4.5 (lower emissions) and RCP8.5 (higher emissions) on the SDGs (Ansuategi et al., 2015) <sup>[[#fn:r46|46]]</sup> . A low emissions pathway allows for greater success in achieving SDGs for reducing poverty and hunger, providing access to clean energy, reducing inequality, ensuring education for all and making cities more sustainable. Even at lower emissions, a medium risk of failure exists to meet goals for water and sanitation, and marine and terrestrial ecosystems.

Action on climate change (SDG 13), including slowing the rate of warming, would help reach the goals for water, energy, food and land (SDGs 6, 7, 2 and 15) (Obersteiner et al., 2016; ICSU, 2017) <sup>[[#fn:r47|47]]</sup> and contribute to poverty eradication (SDG 1) (Byers et al., 2018) <sup>[[#fn:r48|48]]</sup> . Although the literature that connects 1.5°C to the SDGs is limited, a pathway that stabilizes warming at 1.5°C by the end of the century is expected to increase the chances of achieving the SDGs by 2030, with greater potential to eradicate poverty, reduce inequality and foster equity ( ''limited evidence'' , ''medium agreement'' ). There are no studies on overshoot and dimensions of sustainable development, although literature on 4°C of warming suggests the impacts would be severe (Reyer et al., 2017b) <sup>[[#fn:r49|49]]</sup> .

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'''Table 5.1'''

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'''Sustainable development implications of avoided impacts between 1.5°C and 2°C global warming'''

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{| class="wikitable"
|-
! Impacts
! Chapter 3 Section
! 1.5°C
! 2°C
! Sustainable Development Goals (SDGs) More Easily Achieved when Limiting Warming to 1.5°C
|-
| rowspan="2"| Water scarcity
| 3.4.2.1
| 4% more people exposed to water stress
| 8% more people exposed to water stress, with 184–270 million people more exposed
| rowspan="2"| SDG 6 water availability for all
|-
| Table 3.4
| 496 (range 103–1159) million people exposed<br />
and vulnerable to water stress
| 586 (range 115–1347) million people exposed<br />
and vulnerable to water stress
|-
| rowspan="2"| Ecosystems
| 3.4.3,<br />
Table 3.4
| Around 7% of land area experiences biome<br />
shifts
| Around 13% (range 8–20%) of land area<br />
experiences biome shifts
| rowspan="2"| SDG 15 to protect terrestrial ecosystems<br />
and halt biodiversity loss
|-
| Box 3.5
| 70–90% of coral reefs at risk from bleaching
| 99% of coral reefs at risk from bleaching
|-
| rowspan="2"| Coastal cities
| 3.4.5.1
| 31–69 million people exposed to coastal<br />
flooding
| 32–79 million exposed to coastal flooding
| rowspan="2"| SDG 11 to make cities and human settlements safe and resilient
|-
| 3.4.5.2
| Fewer cities and coasts exposed to sea level rise<br />
and extreme events
| More people and cities exposed to flooding
|-
| rowspan="2"| Food systems
| 3.4.6,<br />
Box 3.1
| Significant declines in crop yields avoided,<br />
some yields may increase
| Average crop yields decline
| rowspan="2"| SDG 2 to end hunger and achieve food security
|-
| Table 3.4
| 32–36 million people exposed to lower yields
| 330–396 million people exposed to lower yields
|-
| rowspan="2"| Health
| 3.4.5.1
| Lower risk of temperature-related morbidity<br />
and smaller mosquito range
| Higher risks of temperature-related morbidity<br />
and mortality and larger geographic range<br />
of mosquitoes
| rowspan="2"| SDG 3 to ensure healthy lives for all
|-
| 3.4.5.2
| 3546–4508 million people exposed to heat waves
| 5417–6710 million people exposed to heat waves
|}
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