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

===== 5.5.2.2.5 Adjustments for additional Earth system feedbacks =====

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( [[#5.5.1.2|Section 5.5.1.2]] highlighted recent literature describing potential impacts of Earth system feedbacks that have typically not been included in standard ESMs ( [[#MacDougall--2015|MacDougall and Friedlingstein, 2015]] ; [[#Schneider%20von%20Deimling--2015|Schneider von Deimling et al., 2015]] ; [[#Schädel--2016|Schädel et al., 2016]] ; [[#Burke--2017b|Burke et al., 2017b]] ; [[#Mahowald--2017|Mahowald et al., 2017]] ; [[#Comyn-Platt--2018|Comyn-Platt et al., 2018]] ; [[#Gasser--2018|Gasser et al., 2018]] ; [[#Lowe--2018|Lowe and Bernie, 2018]] ), the most important of which is carbon release from thawing permafrost. The SR1.5 estimated unrepresented Earth system processes to result in a reduction of remaining carbon budgets of up to 100 GtCO <sub>2</sub> over the course of this century, and more thereafter ( [[#Rogelj--2018b|Rogelj et al., 2018b]] ). Here this assessment is updated based on the Earth system feedback assessment of ( [[#5.4.8|Section 5.4.8]] and synthesized in Figure 5.29 by applying the reverse method by [[#Gregory--2009|Gregory et al. (2009)]] .

The assessment in [[#5.4|Section 5.4]] and Box 5.1 highlights the different nature, magnitude and uncertainties surrounding additional Earth system feedback. The remaining carbon budgets reported in Table 5.8 account for these feedbacks, including corrections due to permafrost CO <sub>2</sub> and CH <sub>4</sub> feedbacks as well as those due to aerosol and atmospheric chemistry ( [[#5.4.8|Section 5.4.8]] ). Two of these additional feedbacks (tropospheric ozone and methane lifetime feedbacks) are included in the projections of non-CO <sub>2</sub> warming carried out with AR6-calibrated emulators (Box 7.1). The remainder of these independent Earth system feedbacks combine to a feedback of about 7 ± 27 PgC K <sup>–1</sup> (1-sigma range, or 26 ± 97 GtCO <sub>2</sub> °C <sup>–1</sup> ). Overall, [[#5.4.8|Section 5.4.8]] assessed there to be ''low confidence'' in the exact magnitude of these feedbacks and they represent identified additional amplifying factors that scale with additional warming, and mostly increase the challenge of limiting global warming to or below specific temperature levels.

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