How better time travel will improve climate modelling

Improving how time flows in weather and climate models means better results, and illustrates perfectly how science progresses

The Guardian, Posted by Damian Carrington, Friday 4 February 2011 14.43 GMT

As you read these words, time is flowing smoothly, passing from one moment to the next with no breaks. Reassuring, isn't it?

But in computer models of weather and climate, time has to jump forward in little steps to allow the next set of temperature, rain and other conditions to be calculated from the last. This stepping, Paul Williams at the University of Reading assures me, has the technical name of 'leapfrogging'.

Both weather and climate models currently do a decent job. Weather can be predicted pretty accurately up to about four days ahead and the broad patterns of global climate are well replicated in climate models. That's because over past decades a multitude of researchers have tested and refined the models, improving how they represent the atmosphere and oceans and their interaction.

The one thing that hasn't changed is how time skips along in the models. Back in the early 1980s, the little uncertainties that the leapfrogging introduces were a minor issue compared to the broad challenges of modelling the weather and climate.

But Williams thinks the time has come to improve leapfrogging and he has developed a mathematical tweak that does just that. With colleagues, he has tested his mathematical tweak on weather forecasting models, and the results are published in a journal of the American Meteorological Society.

The addition of just a couple of lines of code to the model led to the five-day weather forecast being as accurate as the old four-day forecast. That would mean 24 hours more notice of what's on the way. And to get climate models right, you need to first get the weather right, so good news there too.

The fact that the tweak is so concise bodes well for its uptake, as it doesn't need modellers to reengineer their millions of lines of code. It is now being tested in over 50 more models.

What I like about this story is it shows perfectly how science works. Researchers spend their time working at the edge of knowledge, focusing on what they can't explain, don't understand or think could be accounted for better.

When scientists talk about uncertainties, they are not saying they are clueless. They are saying they have a working explanation of the world which gives a range of answers, usually a usefully narrow range. With something as crucial as global warming, we should be thankful that diligent scientists across our planet are working every day to make that range even narrower.