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

==== 3.2.4.2 Time of Emergence ====

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Anthropogenic changes in climate-induced drivers assessed here exhibit vastly distinct times of emergence, which is the time scale over which an anthropogenic signal related to climate change is statistically detected to emerge from the background noise of natural climate for a specific region ( [[#Christensen--2007|Christensen et al., 2007]] ; [[#Hawkins--2012|Hawkins and Sutton, 2012]] ). SROCC concluded that for ocean properties, the time of emergence ranges from under a decade (e.g., surface ocean pH) to over a century (e.g., net primary production; see [[#3.4.3.3.4|Section 3.4.3.3.4]] for time of emergence of biological properties; [[#Bindoff--2019a|Bindoff et al., 2019a]] ).

The literature assessed in SROCC mainly focused on surface ocean properties and gradual mean changes. Since then, the time of emergence has also been investigated for subsurface properties, ocean extreme events and particularly vulnerable regions, such as the Arctic Ocean ( [[#Hameau--2019|Hameau et al., 2019]] ; [[#Oliver--2019|Oliver et al., 2019]] ; [[#Burger--2020|Burger et al., 2020]] ; [[#Landrum--2020|Landrum and Holland, 2020]] ; [[#Schlunegger--2020|Schlunegger et al., 2020]] ), but subsequent assessments are ''low confidence'' due to ''limited evidence'' . Below the surface, changes in temperature typically emerge from internal variability prior to changes in oxygen; however, in about a third of the global thermocline, deoxygenation emerges prior to warming ( [[#Hameau--2019|Hameau et al., 2019]] ). Permanent MHW states, defined as when SST exceeds the MHW threshold continuously over a full calendar year, will emerge during the 21st century in many parts of the surface ocean ( [[#Oliver--2019|Oliver et al., 2019]] ). Ocean acidification extremes have already emerged from background natural internal variability during the 20th century in most of the surface ocean ( [[#Burger--2020|Burger et al., 2020]] ). In the Arctic, anthropogenic sea ice changes have already emerged from the background internal variability, and anthropogenic alteration of air temperatures will emerge in the early- to mid-21st century ( [[#Landrum--2020|Landrum and Holland, 2020]] ).

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