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

==== 3.2.4.4 Perspectives from Paleoclimatology Data ====

<div id="h3-10-siblings" class="h3-siblings"></div>

Paleoclimatology observations are useful to assess multiple hazards of environmental change while excluding direct anthropogenic impacts ( [[#3.4.3.3|Section 3.4.3.3]] ). Ancient intervals of rapid climate warming that occurred between 300 and 50 million years ago (Ma) were triggered by the release of greenhouse gases ( ''high confidence'' ). The sources of greenhouse gases varied but include volcanic degassing from continental flood basalts and methane hydrates stored in marine sediments and soils ( [[#Foster--2018|Foster et al., 2018]] ). Six extreme ancient hyperthermal events are known from the last 300 Ma, when tropical SSTs reached 1.5°C–10°C warmer than pre-industrial conditions, and with substantial impacts on ancient life (Cross-Chapter Box PALEO in Chapter 1). Warming and deoxygenation in the oceans were closely associated in hyperthermal events ( ''high confidence'' ), with anoxia reaching the photic zone and abyssal depths ( [[#Kaiho--2014|Kaiho et al., 2014]] ; [[#Müller--2017|Müller et al., 2017]] ; [[#Penn--2018|Penn et al., 2018]] ; [[#Weissert--2019|Weissert, 2019]] ), whereas ocean acidification has not been demonstrated consistently ( ''medium confidence'' ) ( [[#Hönisch--2012|Hönisch et al., 2012]] ; [[#Penman--2014|Penman et al., 2014]] ; [[#Clarkson--2015|Clarkson et al., 2015]] ; [[#Harper--2020a|Harper et al., 2020a]] ; [[#Jurikova--2020|Jurikova et al., 2020]] ; [[#Müller--2020|Müller et al., 2020]] ).

Greenhouse gases also contributed substantially to shaping the longer-term climate trends over the past 50 million years, although changes in continental configuration and ocean circulation as well as planetary orbital cycles were equally important (WGI AR6 Cross-Chapter Box 2.1 in Chapter 2; [[#Westerhold--2020|Westerhold et al., 2020]] ; [[#Gulev--2021|Gulev et al., 2021]] ). There is little evidence for ocean acidification in the past 2.6 Ma ( ''low confidence'' ) ( [[#Hönisch--2012|Hönisch et al., 2012]] ), but ocean ventilation was highly sensitive to even modest warming such as observed in the past 10,000 years ( ''medium confidence'' ) ( [[#Jaccard--2012|Jaccard and Galbraith, 2012]] ; [[#Lembke-Jene--2018|Lembke-Jene et al., 2018]] ).

<div id="3.3" class="h1-container"></div>

<span id="linking-biological-responses-to-climate-induced-drivers"></span>