Abstract: Earth system models (ESMs) are widely used to make conditional statements about the future climate under climate change – in fact, they are the only tools that allow us to do so. Owing to the complexity of the earth system, ESMs come in all shapes and sizes and, as such, they also come with many uncertainties. Leaving aside the uncertainty in the model design and implementation, there are two main sources of uncertainty left: the initial state of the system and the parameter values.

This talk will focus primarily on the latter – the uncertainty that arises from the impossibility of determining exact values for the parameters in the model. This uncertainty is usually assessed via a set (or ensemble) of extra simulations for an alternative, plausible set of parameters – an approach known as parametric, or perturbed physics ensembles (PPEs). However, owing to the high computational cost of running the model, and the large number of parameters in modern ESMs, such PPEs usually consist of a small number of simulations for a small number of hand-picked parameters. But is such ad hoc design enough to make these ensembles informative?

In this talk, I will discuss this problem and, using a conceptual climate-like model, I will present a systematic study of the consequences of parametric uncertainty through a large ensemble approach – over 1,000 members. To conclude, I will discuss the implications for the design and interpretation of climate ensembles.

I endeavour to keep the talk as self-contained and non-technical as possible, so anyone with an interest in the subject is welcome to attend.

Bio: Francisco is a Research Fellow at the London School of Economics (LSE), as part of their Grantham Research Institute. Francisco received BSc, MSc and PhD degrees in Mathematics,before starting a career in environmental science – first as a research scientist in marine biogeochemist at the National Oceanography Centre, and now as a climate scientist at LSE, working primarily on conceptual problems in climate prediction such as the design and interpretation of climate model ensembles, a work that earned him a STEM for BRITAIN award in the Houses of Parliament earlier this year.