Why Do We Need Numerical Ocean Models?

The first lecture explained what an ocean model is. This one, again with Fernand Assene, asks why we need them at all – what is it about the ocean, and about what society needs, that makes numerical models not just useful but indispensable?

The lecture builds the answer in stages:

• The limits of observations – even our finest observing systems leave vast gaps. The Argo array, one of oceanography’s great achievements, has around 4,000 floats spaced ~300 km apart, each profiling once every 10 days and only to 2,000 m depth. Satellites see the whole surface but only its “skin” – they cannot see into the ocean interior. Observations give us sparse dots and tracks in a volumetric sea
• Building the full picture – this is why models are essential. Through data assimilation, sparse observations are combined with model physics to produce a coherent, gap-free, four-dimensional ocean state
• Past, present, and future – a model lets us reconstruct history (hindcast, like the GLORYS12 reanalysis back to 1993), estimate the ocean right now (nowcast, via services such as Copernicus Marine), and predict what’s coming (forecast, such as CMEMS 10-day global forecasts)
• Protecting lives and infrastructure – tracking storm surges, pollutants, and oil spills, giving responders vital lead time
• Powering the blue economy – search and rescue, fuel-saving ship routing, fisheries in the great upwelling systems (including the Canary and Benguela currents off Africa), aquaculture, and swell warnings that protect African ports such as Abidjan, Lomé, Cotonou, and Dar es Salaam
• A laboratory for climate – the ocean absorbs over 90% of excess heat and about 25% of human CO₂, and only models can track where that heat and carbon go, simulate coupled feedbacks, and run the controlled experiments the real ocean will never allow

The takeaway is captured in four reasons we need models: to fill observational gaps, to reproduce the past and constrain the present, to drive operational safety and the blue economy, and to enable virtual experiments about the future. The next lecture opens up the model itself – its anatomy.