December 17, 1997
In an article published in the Dec. 18 issue of Nature magazine, U of T physicist Jerry Mitrovica and Allessandro Forte of the Institut de Physique du Globe de Paris use numerical simulations to show the connection between Earth's changing shape and the gravitational effects of other bodies in the Solar System, particularly Jupiter and Saturn.
"We're showing for the first time that changes in the Earth's shape, when coupled with the gravitational effects from other planets, can produce large changes in the Earth's climate," Mitrovica says.
The evolution of the Earth's precession and obliquity are known to have a long-term impact on climate. Precession refers to the slow movement of the rotation axis in a 26,000-year cycle and obliquity, which varies with a 40,000-year cycle, refers to the tilt of the Earth's axis. As the precession and obliquity change, climate is directly affected because the pattern of the sunshine that falls on the Earth has been altered.
Mitrovica has used numerical simulations to show that these aspects of the Earth's orbit have been affected by the gravitational attraction of Saturn and Jupiter. His figures show that at some time during the last 20 million years, the Earth passed through a gravitational resonance associated with the orbits of Jupiter and Saturn, which in turn influenced the way the Earth's axial tilt changed during the same period. This gravitational pull would have had a much greater impact on the Earth millions of years ago when the Earth was shaped differently.
"To understand climate on Earth it's clear that we need to consider the Earth as this dynamic deforming system," Mitrovica says. "But we also need to understand, more than we thought we did, the Earth's place in the solar system."
This work, part of the emerging discipline of Earth systems science, has broad implications for long-term reconstruction of past and future climate, which in turn may have implications on planetary and human evolution. Mitrovica's research is funded by the Natural Sciences and Engineering Research Council (NSERC) and the Canadian Institute for Advanced Research (Earth Systems Evolution).