The boundaries of a set of regions which are defined in Chapter 14 of the Working Group 1 (WGI) contribution to the 2013 Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and in the AR5 Annex I Atlas of Global and Regional Climate Projections. The regions are used for the calculation of IPCC regional climate statistics.

The regions used to calculate regional climate statistics in AR5 are the 26 SREX regions defined by the IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (IPCC, 2012: also known as "SREX"). For AR5 an additional 7 regions containing the two polar regions, the Caribbean, Indian Ocean and Pacific Island States have been added. In total there are 33 region boundaries and of these, 4 (the Arctic, Antarctic, South Asia and South-East Asia) are used twice for land-only and sea-only analysis, giving a total of 37 IPCC analysis regions.

Each of the 33 regions is provided with a name and a label. The label is set to the three letter code used in the SREX report for the 26 SREX regions. The 7 additional reference regions are also given three letter short names.

The 26 SREX regions are: Alaska/NW Canada (ALA), Eastern Canada/Greenland/Iceland (CGI), Western North America (WNA), Central North America (CNA), Eastern North America (ENA), Central America/Mexico (CAM), Amazon (AMZ), NE Brazil (NEB), West Coast South America (WSA), South- Eastern South America (SSA), Northern Europe (NEU), Central Europe (CEU), Southern Europe/the Mediterranean (MED), Sahara (SAH), Western Africa (WAF), Eastern Africa (EAF), Southern Africa (SAF), Northern Asia (NAS), Western Asia (WAS), Central Asia (CAS), Tibetan Plateau (TIB), Eastern Asia (EAS), Southern Asia (SAS), Southeast Asia (SEA), Northern Australia (NAS) and Southern Australia/New Zealand (SAU).

The non-SREX reference regions are: Antarctica (ANT), Arctic (ARC), Caribbean (CAR), Western Indian Ocean (WIO), Northern Tropical Pacific (NTP), Equatorial Tropical Pacific (ETP) and Southern Tropical Pacific (STP).

The region definitions have a subtlety regarding the treatment of land and sea areas which needs to be handled with care. The climate models use a range of methods for dealing with coastal boundaries. The archived data includes a field giving the proportion of each model grid cell which is land or sea. A model grid cell is considered land if more that 50% of the cell is land. The mean for a given region is then defined in terms of the grid points (which are the cell centres) which are within the specified reference boundaries. The spatial area covered by these grid cells will then differ from model to model. The reference boundaries thus provide a starting point for defining the regional means: the means are not a simple average of these areas. The distinction is not expected to be substantial, but anyone wanting to reproduce exactly the same numbers will need to follow all steps carefully.