This chapter extends the findings of the AR5 by evaluating new scientific evidence on climate system changes and the corresponding impacts on natural and human systems, emphasizing risks associated with 1.5°C of global warming compared to pre-industrial levels.
It examines observed impacts and future risks across various systems, noting significant differences between 1.5°C and 2°C warming scenarios.
Key points include:
1.
**Climate System Changes**: Evidence shows increased land and ocean temperatures, more frequent heatwaves, and heightened marine heatwaves due to human-induced warming.
There's also an increase in the frequency and intensity of heavy precipitation events globally.
2.
**Regional Climate Impacts**: At 1.5°C warming, regional changes include higher temperatures and more extreme weather events.
Overshooting 1.5°C could result in irreversible impacts on ecosystems, requiring urgent CO2 emission reductions.
3.
**Difference Between 1.5°C and 2°C**: Limiting warming to 1.5°C reduces risks of extreme weather, flood hazards, sea-level rise, and ecosystem damage compared to 2°C.
For example, the probability of a sea-ice-free Arctic in summer decreases significantly at 1.5°C.
4.
**Ecosystem and Biodiversity Risks**: Risks of species extinction and changes in ecosystems are notably reduced at 1.5°C compared to 2°C.
The likelihood of coral reef loss is significantly higher at 2°C.
5.
**Human and Economic Impacts**: Risks to human health, food security, and economic growth are less severe at 1.5°C.
Limiting warming to 1.5°C can mitigate impact on water scarcity, agricultural productivity, and urban health issues.
6.
**Small Islands and Coastal Areas**: More severe impacts on small islands and coastal regions increase with global warming, with greater risks at 2°C compared to 1.5°C, including heightened coastal flooding and freshwater stress.
7.
**Increased Reasons for Concern**: Post-AR5, risks have risen in four out of five “Reasons for Concern” categories, emphasizing more severe impacts with every increment of warming, especially from 1.5°C to 2°C.
Overall, the chapter underscores that limiting global warming to 1.5°C instead of 2°C has substantial benefits for both natural and human systems, urging for immediate and significant greenhouse gas mitigation efforts to avoid the more severe consequences of higher warming levels.