Build your own! From tailored box-model climate emulators to pattern scaling

Efficient and interpretable carbon-cycle emulators (CCEs) as part of climate emulators play a key role in Integrated Assessment Models. We present a framework enabling economists to custom-build purpose-tailored multi-reservoir linear box-model CCEs, accurately calibrated to advanced climate science. Three CCEs are presented for illustration: the 3SR model (replicating DICE-2016), the 4PR model (explicitly accounting for a land biosphere carbon reservoir), and the 4PR-X model, which accounts for dynamic land-use changes like deforestation that impact the reservoir's storage capacity and result in a time dependent CCE. We demonstrate that all three models are in line with benchmark data from comprehensive Earth System Models and exemplify how the dynamic land biosphere in the 4PR-X model impacts atmospheric carbon and temperature. The findings highlight the potential and relevance of use-cased tailored, efficient and interpretable climate emulators for economic studies. We complement our 'build your own CCE' toolbox by another set of statistical tools, commonly known as pattern scaling, that allows to go from the global mean temperature change obtained from the climate emulator to regional temperatures and changes thereof. The regional temperatures may be further translated into regional damages. We discuss the relative importance and uncertainty of each building block of this interpretable climate emulator chain, from (dynamic) CCE, to climate emulator, to pattern scaling.