Earth’s changing orbit shows up in tree ring data

Earth’s changing orbit shows up in tree ring data. Under the gravitational influence of Jupiter and Saturn, the eccentricity of Earth’s orbit and the tilt and precession of its rotation axis slowly fluctuate. Those changes affect how much solar radiation reaches a given geographical location and are responsible for Earth’s ice ages. According to a new study, they are also responsible for a more recent phenomenon: the cooling of Scandinavia from 138 BC to AD 1900 at a steady and significant rate of 0.31° per 1000 years. To reach that finding, Jan Esper of Johannes Gutenberg University Mainz in Germany and his collaborators assembled a record of tree rings from the trunks of young and long-dead Scots pines at 17 sites in northern Finland and Sweden. Thanks to the sites’ stability and the availability of buried and submerged trunks, the record is unprecedented in its continuity and consistency. Orbital calculations...