Editing IPCC:AR6/SROCC/Chapter-4 (section)

===== 4.2.3.3.3 Semi-empirical projections =====

Semi-empirical models provide an alternative approach to process-based models aiming to close the budget between the observed SLR and the sum of the different components contributing to SLR. In general, motivated by a mechanistic understanding, semi-empirical models use statistical correlations from time series analysis of observations to generate projections (Rahmstorf, 2007 <sup>[[#fn:r644|644]]</sup> ; Vermeer and Rahmstorf, 2009 <sup>[[#fn:r645|645]]</sup> ; Grinsted et al., 2010 <sup>[[#fn:r646|646]]</sup> ; Kemp et al., 2011 <sup>[[#fn:r647|647]]</sup> ; Kopp et al., 2016 <sup>[[#fn:r648|648]]</sup> ) . They implicitly assume that the processes driving the observations and feedback mechanisms remain similar over the past and future. In the past, differences between semi-empirical projections and process-based models were significant but for more recent studies the differences are vanishingly small. Ongoing advances in closing the sea level budget and in the process understanding of the dynamics of ice have reduced the salience of estimates from semi-empirical models. Moreover, the results from semi-empirical models (Kopp et al., 2016 <sup>[[#fn:r682|682]]</sup> ; Mengel et al., 2016 <sup>[[#fn:r683|683]]</sup> ) are in general agreement with Church et al. (2013) <sup>[[#fn:r684|684]]</sup> , except when those results reflect the combined hydrofracturing and ice cliff instability mechanism as presented by DeConto and Pollard (2016) <sup>[[#fn:r685|685]]</sup> . At the same time, semi-empirical models based on past observations capture poorly or miss altogether the recent observed changes in Antarctica. MISI may lend a very different character to ice sheet evolution in the near future than in the recent past and hydrofracturing remains impossible to quantify from observational records only. For this reason, a new generation of semi-empirical models and emulators has been developed that estimate individual components of SLR, which the former models do not (Mengel et al., 2018 <sup>[[#fn:r686|686]]</sup> ) . These newer models aim to emulate the response of more complex models providing more detailed information for different climate scenarios or probability estimates than process-based models (Bakker et al., 2017 <sup>[[#fn:r687|687]]</sup> ; Nauels et al., 2017a <sup>[[#fn:r688|688]]</sup> ; Wong et al., 2017 <sup>[[#fn:r689|689]]</sup> ; Edwards et al., 2019 <sup>[[#fn:r690|690]]</sup> ) .

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