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

=== 5.4.6 Emergent Constraints to Reduce Uncertainties in Projections ===

<div id="h2-26-siblings" class="h2-siblings"></div>

Emergent constraints are based on relationships between observable aspects of the current or past climate (such as trends or variability), and uncertain aspects of future climate change (such as the strength of particular feedbacks). These relationships are evident across an ensemble of models. When combined with an observational estimate of the trend or variability in the real climate, such emergent relationships can yield ‘emergent constraints’ on future climate change ( [[#Hall--2019|Hall et al., 2019]] ). At the time of AR5 (WGI, Section 9.8.3), there had been relatively few applications of the technique to constrain carbon cycle sensitivities, but there have been many studies published since (e.g., the summary in [[#Cox--2019|Cox, 2019]] ). Figure 5.28 shows some key published emergent constraints on the carbon cycle in ESMs.

<div id="_idContainer077" class="Basic-Text-Frame"></div>

[[File:11335dd156d2654759d973cf07e96dad IPCC_AR6_WGI_Figure_5_28.png]]

'''Figure 5.28 |''' '''Examples of emergent constraints on the carbon cycle in Earth system models (ESMs)''' , reproduced from previously published studies: '''(a)''' projected global mean atmospheric carbon dioxide (CO <sub>2</sub> ) concentration by 2060 under the RCP8. 5 emissions scenario against the simulated CO <sub>2</sub> in 2010 ( [[#Friedlingstein--2014b|Friedlingstein et al., 2014b]] ; [[#Hoffman--2014|Hoffman et al., 2014]] ); '''(b)''' sensitivity of tropical land carbon to warming ( γ <sub>LT</sub> ) against the sensitivity of the atmospheric CO <sub>2</sub> growth-rate to tropical temperature variability ( [[#Cox--2013|Cox et al., 2013]] ; [[#Wenzel--2014|Wenzel et al., 2014]] ); '''(c)''' sensitivity of extratropical (30°N–90°N) gross primary production to a doubling of atmospheric CO <sub>2</sub> against the sensitivity of the amplitude of the CO <sub>2</sub> seasonal cycle at Kumkahi, Hawaii to global atmospheric CO <sub>2</sub> concentration ( [[#Wenzel--2016|Wenzel et al., 2016]] ); '''(d)''' change in high-latitude (30°N–90°N) gross primary production versus trend in high-latitude leaf area index or ‘greenness’ ( [[#Winkler--2019|Winkler et al., 2019]] ); '''(e)''' sensitivity of the primary production of the Tropical Ocean to climate change versus its sensitivity to El Niño–Southern Oscillation (ENSO)-driven temperature variability ( [[#Kwiatkowski--2017|Kwiatkowski et al., 2017]] ); '''(f)''' global ocean carbon sink in the 2090s versus the current-day carbon sink in the Southern Ocean. In each case, a red dot represents a single ESM projection, the grey bar represents the emergent relationship between the y-variable and the x-variable, the blue bar represents the observational estimate of the x-axis variable, and the green bar represents the resulting emergent constraint on the y-axis variable. The thicknesses represent ± one standard error in each case. Figure after [[#Cox--2019|Cox (2019)]] . Further details on data sources and processing are available in the chapter data table (Table 5.SM.6).

<div id="5.4.7" class="h2-container"></div>

<span id="climate-feedbacks-from-ch-4-and-n-2-o"></span>