Editing IPCC:AR6/WGII/Chapter-16 (section)

===== Temperature overshoot =====

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The concept of temperature overshoot, defined as ‘exceedance of a specified global warming level followed by a decline to or below that level during a specified period of time’ is a relevant consideration for this RFC risk assessment; however, the effect of overshoot has not explicitly been considered in the burning ember assessment because of the limited literature basis. However, despite the lack of directly assessed overshoot scenarios, the current literature provides several salient examples of irreversible changes that are projected to occur once global temperatures reach a particular level. For example, coral reefs are unable to survive repeated bleaching events that are too close together, leading to irreversible loss of the reefs even if bleaching were to cease (see [[#16.6|Section 16.6.3.1]] RFC1). Species extinction is irreversible, and [[IPCC:Wg2:Chapter:Chapter-2|Chapter 2]] assesses that, at ~1.6°C, &gt;10% of species are projected to become endangered as compared with &gt;20% at ~2.1°C (median), representing high and very high biodiversity risk, respectively ( ''medium confidence'' ) ( [[IPCC:Wg2:Chapter:Chapter-2#2.5.4|Section 2.5.4]] ). Similarly, WGI AR6 finds that ‘Over the 21st century and beyond, abrupt and irreversible regional changes in the water cycle, including changes in seasonal precipitation, streamflow and aridity, cannot be excluded’. Thus, information about irreversibility provides information about the potential outcome of temperature overshoot scenarios. Other types of losses, such as loss of human or species life, are irreversible even if the loss process ceases in the future. The less resilient a system is, the more likely it is to suffer irreversible damage during a temperature overshoot; the more resilient it is, the more likely it is to be able to withstand the overshoot or recover afterwards. Very high levels of risk, as assessed here in the RFC, are associated with a wide range of criteria for risk assessment including irreversibility. While not all very high risks are irreversible, in general, risks reaching a very high level include a component of irreversible risks that would persist during and after an overshooting of a given temperature level.

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