The ACCESS-NRI team has added a “time dial” into the Earth System Model (EM1.5) that allows paleoclimate researchers to match the right value of Earth’s orbit around the Sun during different past climates.
The Earth System Model 1.5 (ESM1.5) is used by the paleoclimate community to understand the climate of the Earth from thousands to millions of years ago. The ACCESS-NRI team have now included more features in the new release of ESM1.5, making their work easier, faster and more precise.
ACCESS-NRI research software engineer Spencer Wong, who developed this new feature, says that “previously, the parameters that determine Earth’s orbit were embedded in the code and researchers couldn’t change these themselves. This meant that if you wanted to simulate different times, you had to rebuild the model again, which was a frustrating process”.
There are three ways that Earth’s orbit changes through time: (1) obliquity, or the “tilt” of the Earth’s
Summer precipitation anomalies following a shutdown of the Atlantic Meridional Overturning Circulation as simulated by the ACCESS-ESM1.5 (Saini et al.,. 2025, Paleoceanography & Paleoclimatology, in press)
rotation with respect to the sun, (2) eccentricity; which is the non-circularity or “oval” shape of Earth’s orbit around the sun, and (3) precession, which determines when in the year the Earth is closest to or furthest away from the sun. These three orbital parameters play a critical role in shaping the planet’s climate as they affect Earth’s incoming solar radiation as a function of days of the year and latitude.
“We worked closely with members of the paleoclimate community to co-design this feature and make the model easier to use, saving researchers a lot of time”, he says.
Paleoclimate researcher Dr Laurie Menviel, from the Australian Centre of Excellence in Antarctic Science (ACEAS) at the UNSW Sydney, investigates glacial and interglacial cycles as well as abrupt climate changes linked to changes in the ocean’s circulation.
“In the past, it was quite difficult for us to modify the Earth’s orbital parameters in the model’s code. Being able to modify these parameters ourselves has significant implications for our work, as they are one of the key drivers of the glacial-interglacial cycles, that were the dominant mode of natural climate variability of the last million years,” she says.
Sea-surface salinity anomaly following a weakening of the Atlantic Meridional Overturning Circulation as simulated by the ACCESS-OM2-025 (Pontes & Menviel, 2024, Nature Geosciences).
The orbital parameters have a strong impact on Earth’s climate and on summers and winters becoming either milder, or more extreme. Mild (i.e., cooler) summers are more conducive to glacial periods, while extreme (i.e., hot) summers are more conducive to interglacial periods. This is because the build-up of glaciers from year-to-year depends most strongly on having a relatively cool summer, for the ice to survive.
Recently, her team participated in the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 to simulate the climate of the Last Interglacial (~127,000 years ago).
“During that time, the climate was warmer than during pre-industrial times, the Arctic was almost ice-free and the sea-level was probably higher than today by 2 to 5m. As the last Interglacial could be used as an analogue for future climates, it is important to understand the feedbacks that led to a loss of Arctic sea-ice and higher sea-levels”, she says.
Paleoclimates provide a unique perspective on climate change by allowing researchers to understand the feedbacks involved in climate change processes as well as testing climate models. This can ultimately help improve current climate models.
“We are trying to make projections for a climate that is changing very quickly. Using past climates, you can compare the model outputs with proxy records which help you to evaluate the accuracy of the model and learn about its sensitivity to abrupt changes”, says Dr Menviel.