365 Days of Climate Awareness 326 – Hindcasting

One of the most powerful tools we have for testing and tuning climate models is “hindcasting”, where the model is run over a historical period, usually decades long. The starting, intermediate and end conditions are already known, so the model’s results can be compared statistically to the historical data. A small side benefit of this method is that, when the model is found to give historically robust results, the model itself can be used to provide insights about parts of the globe which have been inadequately monitored through the years.

Tidal level model hindcasting.

Accuracy through a prior range in time is not a guarantee of accuracy into the future. Predictions are hard! And conditions, such as greenhouse gas inputs, change. We are limited by the relatively recent development of our climate monitoring capabilities, and the immediacy of the impacts of global warming. We don’t have a long timespan of direct measurements, or a leisurely run of decades to come in which to build our base of knowledge. Climate is changing, now, with increasing speed.

NASA verification of global temperature model average against actual.

For its imperfection, hindcasting is still a primary tool of climate modelers. Increasing computer speed and more detailed information about conditions in the atmosphere, ocean and the rest of the biosphere provide the means for modelers to make more comprehensive, higher-resolution models. The more variables around the globe which can be controlled for, from basics like temperature, humidity and albedo, to more advanced types such as evapotranspiration rates and oceanic gas and heat fluxes, the more robust the model will be.

1)     El Niño/Southern Oscillation (ENSO) hindcasting. Rather more complicated than water level at a single tidal station!

This is why predictive climate model runs normally include a hindcasting run-up of several decades, to establish that any given model run is as true to known data as we can make it. It’s a regular, common-sense verification like any equipment safety checklist.

Tomorrow: model results from the IPCC’s Sixth Assessment Report (AR6).

Be brave, be steadfast, and be well.