According to the World Meteorological Organization (WMO), climate models incorporate the physics and chemistry of the atmosphere and the oceans and aim to answer questions such as when the next El Niño might occur, and what might happen if greenhouse gas concentrations double.

Climate models were developed from weather forecasting models but, due to the large number of calculations involved, climate models currently use bigger grid spacing and longer time steps so that they can be run further ahead in time for a given amount of computer time, according to the WMO.

The National Academy of Sciences (NAS) put together a short video on the basics of climate modeling. Video courtesy of the NAS and YouTube.

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Are climate models improving?

The Intergovernmental Panel on Climate Change (IPCC) tried to answer this question in their fifth assessment report.

The complexity of climate models compared to those as recently as 25 years ago has increased substantially, so in that sense, current Earth System Models are vastly ‘better’ than the models of that era, according to the IPCC.

Atmospheric model schematic

The IPCC goes on to say that climate models of today are, in principle, better than their predecessors. However, every bit of added complexity, while intended to improve some aspect of simulated climate, also introduces new sources of possible error. We also see these new sources of error with some of the newer, more complex weather forecasting models.

Image courtesy of the IPCC.

When I began my career at AccuWeather 26 years ago there were just a handful of weather forecast models that were available and just a few of those were actually used on a day to day basis. Today, there are dozens of models, ranging from global models to high resolution regional models. The regional models are very useful for situations such as lake-effect snow and thunderstorm prediction. Global models are getting much better at longer range weather prediction than what they were just 10-15 years ago.

An important consideration is that model performance can be evaluated only relative to past observations, taking into account natural internal variability. To have confidence in the future projections of such models, historical climate—and its variability and change—must be well simulated. (via the IPCC AR5)

The IPCC makes an important point below....

Whereas weather and seasonal climate predictions can be regularly verified, climate projections spanning a century or more cannot. This is particularly the case as anthropogenic forcing is driving the climate system toward conditions not previously observed in the instrumental record, and it will always be a limitation.

The IPCC notes that some models perform better than others for certain climate variables, but that no individual model clearly emerges as ‘the best’ overall.

Finally, the IPCC concludes....

So, yes, climate models are getting better, and we can demonstrate this with quantitative performance metrics based on historical observations. Although future climate projections cannot be directly evaluated, climate models are based, to a large extent, on verifiable physical principles and are able to reproduce many important aspects of past response to external forcing. In this way, they provide a scientifically sound preview of the climate response to different scenarios of anthropogenic forcing.

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