Convergence of model projections is often considered by climate scientists to be an important objective in so far as it may indicate the robustness of the models’ core hypotheses. Consequently, the range of climate projections from a multi-model ensemble, called “model spread”, is often expected to reduce as climate research moves forward. However, the successive Assessment Reports of the Intergovernmental Panel on Climate Change indicate no reduction in model spread, whereas it is indisputable that climate science has made improvements in its modelling. In this paper, after providing a detailed explanation of the situation, we describe an epistemological setting in which a steady (and even slightly increased) model spread is not doomed to be seen as negative, and is indeed compatible with a desirable evolution of climate models taken individually. We further argue that, from the perspective of collective progress, as far as the improvement of the products of a multi-model ensemble (e.g. means) is concerned, reduction of model spread is of lower priority than model independence.

气候科学家通常认为模式预测的收敛性是一个重要目标，因为它可能表明模式核心假设的稳健性。因此，随着气候研究的推进，多模式集合的气候预测范围（称为“模式传播”）通常预计会减少。然而，政府间气候变化专门委员会的连续评估报告表明模式传播并没有减少，而气候科学在其建模方面有所改进是无可争议的。在本文中，在详细解释了这种情况后，我们描述了一种认识论环境，其中稳定（甚至略微增加）的模型传播并不注定被视为负面，并且确实与气候模型的理想演变相兼容单独采取。