To assess climate and climate change related to the Barents Sea, the Nansen Legacy uses output from the CMIP5 and CMIP6 archives.

The Climate Model Intercomparison Project (CMIP) was established in 1995 by the World Climate Research Program (WCRP) to provide climate scientists with a database of coupled climate model simulations. The CMIP process involves research institutions from around the world running their climate models with an agreed set of input parameters to produce a multi-model dataset designed to advance our knowledge of climate.

The most recently completed phase of the project (2010-2014) is CMIP5. Results from CMIP5 models were used in the IPCC AR5 report. The sixth phase of the Coupled Model Intercomparison Project (CMIP6) is currently in progress. Different simulations are available as part of the CMIP output. The most frequently used are:

Pre-industrial control simulations: Forced by non-evolving pre-industrial conditions, which may include prescribed atmospheric concentrations or non-evolving emissions of gases, aerosols. Used to understand natural (internal) variability of the climate system.

Historical simulations: Impose changing conditions (consistent with observations from 1850-2005).

Future emission scenarios: Future projections (2006-2100) forced by different emission scenarios. In CMIP5, these were referred to as representative concentration pathways (RCP) corresponding to the radiative forcing in year 2100 relative to pre-industrial conditions (e.g., RCP8.5 corresponds to an additional 8.5 W/m2). For CMIP6, Shared Socioeconomic Pathways (SSPs) scenarios are used. For example, the two future scenarios SSP126 and SSP585 represent a low-emission and a high-emission scenario, in which strong economic growth is fueled via sustainable and fossil fuel pathways, respectively.