Effects of Observational Uncertainty and Models Similarity on Climate Change Projections

Abstract

Climate change projections (CCPs) are based on the multimodel means of individual climate model simulations that are assumed to be independent. However, model similarity leads to projections biased toward the largest set of similar models and the underestimation of uncertainties. We assessed the influence of similarities in CMIP6 through CMIP3 CCPs. We ascertained model similarity due to shared physics/dynamics and initial conditions by comparing simulated spatial temperature and precipitation with the corresponding observed patterns and accounting for inter-model spread relative to the spread across observational datasets. After accounting for similarity, the information from 57 CMIP6, 47 CMIP5, and 24 CMIP3 models could be explained by just 11 effective models, without significant differences in globally averaged climate change statistics. The effective models showed a smaller globally averaged temperature rise of 0.25ºC (~0.5ºC–1ºC in some regions) by the end of 21 century relative to the multimodel mean of all models for socioeconomic pathways 5–8.5.