Editing IPCC:AR6/WGI/Chapter-10 (section)

==== 10.3.1.1 Global Models, Including High-resolution and Variable Resolution Models ====

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Model-based regional climate projections are all based upon some type of global model, including state-of-the-art Earth system models (ESMs), coupled atmosphere–ocean general circulation models (GCMs) or atmosphere-only general circulation models (AGCMs) (see [[IPCC:Wg1:Chapter:Chapter-1#1.5.3.1|Section 1.5.3.1]] ). They are collectively referred to as global models.

State-of-the-art global models are generally used to derive climate information at continental to global scales both for past and future climates (e.g., Chapters 3 and 4). The nominal horizontal resolution in CMIP5 global models is typically 100–200 km. The effective resolution, for which the shape of the kinetic energy spectrum is simulated correctly, is about three to five times larger ( [[#Klaver--2020|Klaver et al., 2020]] ), and a similar relationship also applies to RCMs ( [[#Skamarock--2004|Skamarock, 2004]] ). This strongly limits their ability to resolve local details. Since AR5 the progress in reducing biases and providing more credible regional projections by global models has been moderate in spite of the more realistic representation of a number of processes and the increase in resolution of some models. For AR6, several of the new CMIP6 ( [[#Eyring--2016a|Eyring et al., 2016a]] ) model intercomparison projects (MIPs) address some of these limitations. The list of MIPs is provided in [[IPCC:Wg1:Chapter:Chapter-1|Chapter 1]] (Table 1.3). High-Resolution MIP (HighResMIP; [[#Haarsma--2016|Haarsma et al., 2016]] ) and Global Monsoons MIP (GMMIP; [[#Zhou--2016|Zhou et al., 2016]] ) specifically address the regional climate challenge using global models. HighResMIP focuses on producing global climate projections at a horizontal resolution of around 50 km grid spacing or finer while GMMIP aims at better understanding and predicting the monsoons.

An alternative to increasing resolution everywhere is offered by variable resolution global models, that is, with regionally finer resolution. They have been developed since the 1970s ( [[#Li--1999|Li, 1999]] ), resulting in a first coordinated effort (SGMIP) by Fox-Rabinovitz et al. (2006, 2008). They are expected to offer the finest resolution possible in the region of interest, while still resolving the climate processes at the global scale (although at lower resolution). An overview of recent developments is in [[#McGregor--2015|McGregor (2015)]] . This is a rapidly developing field ( [[#Krinner--2014|Krinner et al., 2014]] ; [[#Ferguson--2016|Ferguson et al., 2016]] ; [[#Huang--2016|Huang et al., 2016]] ) that will possibly contribute to improved future regional projections.

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