New article in Science Advances shows that climate models are able to perform under different climate conditions

This is one of the rare cases when climate models are tested against empirical observations in a different climate. Precipitation from models reflects fairly well patterns from the available geological evidence. In a past period when climate was warmer than now in the northern hemisphere, boreal monsoon systems where likely much stronger.

12/02/2019 | 5:06 PM

An international team of environmental scientists and climatologists, led by VU and IVM scientist Paolo Scussolini, tested climate models using geological evidence from a key period in the earth’s history. The research was published lasts week in Science Advances. From the VU, also Pepijn Bakker was part of the team, and from the IVM, also Dim Coumou, Philip Ward and Jeroen Aerts.

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.

The problem is that it is commonly only possible to test climate models using recent observations. But it  is important to know whether models can also correctly simulate climates outside of the narrow modern range. To do that, we need to look into the earth’s deeper past. Very interesting in here is the Last Interglacial (ca. 125,000 years ago), the most recent period when climate was warmer than now, at least in the Northern Hemisphere.

The team took two approaches. First, they looked at differences in precipitation between simulations the Last Interglacial and of the Pre-Industrial periods, using the latest generation (CMIP6 / PMIP4) of seven global climate models. Second, they synthesized the empirical knowledge on Last Interglacial precipitation from decades of geological fieldwork around the globe: from fossils, speleothems, marine sediment, etc.

It turns out that the models capture the main features of past precipitation from the geological ‘proxies’ quite well in the Northern Hemisphere (see figure: blue is where the Last Interglacial was wetter than the Pre-Industrial). There, models and ‘proxies’ agree that climate was wetter, 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’s high latitudes, is 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.