Evaluation of biospheric components in Earth system models using modern and palaeo-observations: the state-of-the-art

[摘要] Earth system models (ESMs) are increasing in complexity by incorporating moreprocesses than their predecessors, making them potentially important toolsfor studying the evolution of climate and associated biogeochemical cycles.However, their coupled behaviour has only recently been examined in anydetail, and has yielded a very wide range of outcomes. For example, coupledclimate–carbon cycle models that represent land-use change simulate totalland carbon stores at 2100 that vary by as much as 600 Pg C, given the sameemissions scenario. This large uncertainty is associated with differences inhow key processes are simulated in different models, and illustrates thenecessity of determining which models are most realistic using rigorousmethods of model evaluation. Here we assess the state-of-the-art inevaluation of ESMs, with a particular emphasis on the simulation of thecarbon cycle and associated biospheric processes. We examine some of the newadvances and remaining uncertainties relating to (i) modern and palaeodataand (ii) metrics for evaluation. We note that the practice of averagingresults from many models is unreliable and no substitute for properevaluation of individual models. We discuss a range of strategies, such asthe inclusion of pre-calibration, combined process- and system-levelevaluation, and the use of emergent constraints, that can contribute to thedevelopment of more robust evaluation schemes. An increasingly data-richenvironment offers more opportunities for model evaluation, but also presentsa challenge. Improved knowledge of data uncertainties is still necessary tomove the field of ESM evaluation away from a "beauty contest" towards thedevelopment of useful constraints on model outcomes.

[学科分类] 地球化学与岩石