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 intermodel uncertainty underestimation. We assessed the influences of similarities in CMIP6 through CMIP3 CCPs. We ascertained model similarity from shared physics/dynamics and initial conditions by comparing simulated spatial temperature and precipitation with the corresponding observed patterns and accounting for intermodel spread relative to the observational uncertainty, which is also critical. After accounting for similarity, the information from 57 CMIP6, 47 CMIP5, and 24 CMIP3 models can be explained by just 11 independent models without significant differences in globally averaged climate change statistics. On average, independent models indicate a lower global-mean temperature rise of 0.25 °C (~0.5 °C–1 °C in some regions) relative to all models by the end of the 21st century under CMIP6’s highest emission scenario.

气候变化预测 (CCP) 基于假定独立的各个气候模型模拟的多模型方法。然而，模型相似性导致预测偏向于最大的一组相似模型，并且低估了模型间的不确定性。我们通过 CMIP3 CCP 评估了 CMIP6 中相似性的影响。我们通过将模拟的空间温度和降水与相应的观测模式进行比较，并考虑相对于观测不确定性的模型间传播（这也很重要），从共享的物理/动力学和初始条件确定了模型的相似性。考虑相似性后，来自 57 个 CMIP6、47 个 CMIP5 的信息，24个CMIP3模型只需11个独立模型就可以解释，全球平均气候变化统计数据没有显着差异。平均而言，独立模型表明，到 21 世纪末，在 CMIP6 最高排放情景下，全球平均温升将比所有模型低 0.25 °C（某些地区~0.5 °C–1 °C）。