Astronomical cycles changed the climate 200 million years ago

It is well understood for the past three million years that the interactions between the celestial bodies in the solar system periodically change the Earth's climate: "We know that ice age cycles were caused by the fact that the Earth's orbit and its intrinsic rotation axis periodically change due to the gravitational forces of the planets and the Earth's moon - and this in turn influences solar radiation and thus the climate," explains palaeoclimate researcher Jan Landwehrs from PIK and the University of Vienna. These cycles are one of the most important natural drivers of global climate change in the Earth's recent history and are particularly responsible for the past ice ages. However, how this also influenced warmer climate phases with higher greenhouse gas concentrations in Earth's earlier history has been undetermined until now.

New climate model shows influence of astronomical forces

The new study shows the influence of other celestial bodies on the Earth's climate for the Late Triassic and Early Jurassic (i.e. about 230 to 200 million years ago) as well, a time of global warming and high CO2 concentrations in the atmosphere, when dinosaurs already populated the supercontinent Pangaea. For this purpose, the research team examined sediment cores from the Newark-Hartford Basin in the eastern USA, which was located in the tropics of Pangaea 233 to 199 million years ago and slowly migrated northwards (from 5° to 20°N).

"From this geological archive, we can see that the water level of large lakes rose and fell repeatedly within a few thousand years. Based on this, we were able to show through climate simulations that astronomical forces are an important factor in climate change, along with the CO2 levels in the atmosphere and tectonic plate movements," Landwehrs explains.

To map the extraterrestrial influence, simulations were carried out with the newly developed CLIMBER-X Earth system model: "This particularly fast model made it possible for the first time to dynamically simulate such climatic cycles for periods far in the past," explains co-author Georg Feulner of the Potsdam Institute for Climate Impact Research.

Climate crisis and mass extinction

The results explain the past, but are also interesting for the future, "in terms of how the current climate crisis and a future greenhouse climate can be simulated and thus predicted", emphasises co-author Michael Wagreich from the Institute of Geology at the University of Vienna. At the Triassic-Jurassic transition 200 million years ago, the climate changed drastically due to volcanic CO2 emissions, among other things, and one of the largest mass extinctions in the history of the Earth occurred.

Even though many factors interacted and earlier changes often took place over much longer periods of thousands of years, the strong influence of CO2 on the climate is evident in each case: "If we do not quickly limit greenhouse gases in the atmosphere, our time will go down in Earth history as that of the sixth great mass extinction", warns Wagreich.