Editing IPCC:AR6/SR15/TS (section)

=== Increased Reasons for Concern ===

'''There are multiple lines of evidence that since AR5 the assessed levels of risk increased for four of the five Reasons for Concern (RFCs) for global warming levels of up to 2°C (''high confidence'').''' The risk transitions by degrees of global warming are now: from high to very high between 1.5°C and 2°C for RFC1 (Unique and threatened systems) (''high confidence''); from moderate to high risk between 1°C and 1.5°C for RFC2 (Extreme weather events) (''medium confidence''); from moderate to high risk between 1.5°C and 2°C for RFC3 (Distribution of impacts) (''high confidence''); from moderate to high risk between 1.5°C and 2.5°C for RFC4 (Global aggregate impacts) (''medium confidence''); and from moderate to high risk between 1°C and 2.5°C for RFC5 (Large-scale singular events) (''medium confidence''). {3.5.2}

# '''The category ‘Unique and threatened systems’ (RFC1) display a transition from high to very high risk which is now located between 1.5°C and 2°C of global warming''' as opposed to at 2.6°C of global warming in AR5, owing to new and multiple lines of evidence for changing risks for coral reefs, the Arctic and biodiversity in general (''high confidence''). {3.5.2.1}
# '''In ‘Extreme weather events’ (RFC2), the transition from moderate to high risk is now located between 1.0°C and 1.5°C of global warming,''' which is very similar to the AR5 assessment but is projected with greater confidence (''medium confidence''). The impact literature contains little information about the potential for human society to adapt to extreme weather events, and hence it has not been possible to locate the transition from ‘high’ to ‘very high’ risk within the context of assessing impacts at 1.5°C versus 2°C of global warming. There is thus ''low confidence'' in the level at which global warming could lead to very high risks associated with extreme weather events in the context of this report. {3.5}
# '''With respect to the ‘Distribution of impacts’ (RFC3) a transition from moderate to high risk is now located between 1.5°C and 2°C of global warming,''' compared with between 1.6°C and 2.6°C global warming in AR5, owing to new evidence about regionally differentiated risks to food security, water resources, drought, heat exposure and coastal submergence (''high confidence''). {3.5}
# '''In ‘global aggregate impacts’ (RFC4) a transition from moderate to high levels of risk is now located between 1.5°C and 2.5°C of global warming,''' as opposed to at 3.6°C of warming in AR5, owing to new evidence about global aggregate economic impacts and risks to Earth’s biodiversity (''medium confidence''). {3.5}
# '''Finally, ‘large-scale singular events’ (RFC5), moderate risk is now located at 1°C of global warming and high risk is located at 2.5°C of global warming,''' as opposed to at 1.6°C (moderate risk) and around 4°C (high risk) in AR5, because of new observations and models of the West Antarctic ice sheet (''medium confidence''). {3.3.9, 3.5.2, 3.6.3}