24 000 years of climate change, mapped
The researchers used a technique called data assimilation—a way of seamlessly melding discrete measurements with the output of a numerical model—that’s widely used in forecast meteorology. Extending the method’s time horizon from days to thousands of years was a daunting computational challenge. To make it work, they used a so-called off-line approach, which involved running the climate model only once, as opposed to the meteorologists’ “online” method of repeatedly rerunning a model to incorporate new data and refine a weather forecast.