Climate models compared to geological evidence

An international team of environmental scientists and climatologists, led by VU scientist Paolo Scussolini, tested climate models using geological evidence from earlier times. By studying the geological past we can learn important lessons about the future of our climate.

11/20/2019 | 8:30 PM

The research was published this week in Science Advances. From the VU, also Pepijn Bakker, Dim Coumou, Philip Ward and Jeroen Aerts were involved in the research.

To understand climate, researchers need realistic theoretical representations of it: global climate models. If these models can replicate real, observed past climate, there is confidence that they will do a reasonable job of projecting future changes.

Projections are essential for society, to inform decisions and to adapt. While climate models are routinely tested versus recent climate observations, it is important to know whether they can correctly simulate climates outside of the narrow modern range.

The Last Interglacial
This is only possible by looking into the earth’s deeper past. An especially interesting possibility is offered by the Last Interglacial (ca. 125,000 years ago), the most recent period when climate was warmer than now, at least in the Northern Hemisphere.

In their study, the research team took two approaches. First, they simulated the Last Interglacial and the Pre-Industrial periods using the latest generation (CMIP6) of seven global climate models, and they calculated a map of the differences in precipitation between the two climates. Second, they synthesized the empirical knowledge on Last Interglacial precipitation from existing results of decades of geological fieldwork around the globe: from fossils, speleothems, marine sediment, etc.

Models work well
Comparing models to the geological evidence, it turns out that the models are able to capture the main features of past precipitation quite well in the Northern Hemisphere. There, models and empirical evidence agree that precipitation was stronger, mostly over the monsoon areas and at the high latitudes. The Southern Hemisphere may have been drier, but this is less clear.

The Last Interglacial is not a proper analogue for the future climate we expect: whereas back then warming was due to a different distribution of the solar radiation reaching the earth, future warming will be due to higher concentration of greenhouse gas.

Nevertheless, the marked warming of the Northern Hemisphere, especially at high latitudes, is indeed a compelling similarity between the two climates. It is therefore plausible that the mechanisms behind the increase in Last Interglacial precipitation still hold for the ongoing climatic change, so here we may also have a lesson for possible futures.