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

== Atlas.12 Final Remarks ==

<div id="h1-13-siblings" class="h1-siblings"></div>

Developing from the AR5 WGI Atlas Annex ( [[#IPCC--2013a|IPCC, 2013a]] ), the Atlas is an innovation in the WGI contribution to the AR6, providing a region-by-region assessment of new knowledge on changes in mean climate and an online interactive tool, the Interactive Atlas. It demonstrates the diversity in the climate changes across these regions, in the evidence base for generating information on what changes have already occurred and why, and what further changes each region is projected to face in the future based on different emissions scenarios and global warming levels. Finally, the Interactive Atlas allows for further exploration of the data underpinning the assessment material generated by many of the other chapters.

The foundation of the regional information generated by the Atlas chapter is an assessment of the significant body of new literature on regional climate change though noting substantial heterogeneity in both its availability and the involvement of regional expertise. In many regions this allows for an in-depth assessment though in some the range of information that can be provided and/or the level of confidence in the information is limited. There is similar heterogeneity in the availability of observations to assess recent trends and evaluate model performance, with a lack of curated regional datasets in the polar regions, Northern South America, Africa and the Small Islands.

Internal variability is a large contributor to the climate uncertainty at regional scales. Recent work has combined outputs of single model initial-conditions large ensembles (SMILEs) with CMIP5 and CMIP6 to partition and gain insights on the modelled range and uncertainty arising from internal variability and from model-response uncertainty for a given emissions scenario ( [[#Deser--2020|Deser et al., 2020]] ; [[#Lehner--2020|Lehner et al., 2020]] ; [[#Maher--2021|Maher et al., 2021]] ). The work highlights the notable role for internal variability at regional scales, particularly for precipitation in regions with weaker forced response, where internal variability can remain larger than model uncertainty or scenario uncertainty throughout the whole century. The Atlas (similarly to other regional chapters) uses a single realization per model (CMIP6 models provide multiple realizations, but it is not the case for CORDEX and less so for CMIP5), which allows for the comparison of the different lines of evidence but at the expense of internal variability having a larger influence on the ability to detect or quantify changes.

The assessment produced in the Atlas is based on the individual results from the different lines of global and regional evidence and the consistency amongst them, as there is a lack of literature on methodologies that combine multiple lines of evidence to distil regional climate change information.

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