While astrology is nonsense, Earth and the life on it are certainly deeply affected by cosmic influences.
For example, variations in the eccentricity of Earth's elliptical orbit around the Sun, as well as the tilt of its spin axis, are driven by the shifting balance of gravitational tugs from the Moon and the Sun, as well as the giant outer planets, especially Jupiter.
These so-called Milankovitch cycles cause rhythmical variations in the intensity of the seasons and Earth’s overall climate.
The pulse of ice ages over the past 2.5 million years, for instance, is governed by the Milankovitch cycles.
Slight variations in the Sun may also affect climate in smaller ways, such as periods when the solar magnetic field is weaker – meaning there are fewer sunspots – allow more galactic cosmic rays to reach Earth, potentially triggering greater cloud formation.
Scientists studying Earth’s past climatic conditions rely on various sources of information, such as the ratio of different isotopes in Antarctic ice cores, sediments at the bottom of lakes and oceans, and tree rings.
Trees are sensitive to factors such as temperature and rainfall, so the rings of growth they produce in their branches and trunks each year serve as recorders of that area’s local climate
Tree rings are generally thicker in warm and wet years.
Tree ring data may therefore reveal shorter-term patterns of variation in Earth’s climate.
Vincent Courtillot and his colleagues at the Paris Institute of Earth Physics, Paris Cité University, studied a very special tree ring data set made available by Ouya Fang at the Chinese Academy of Sciences, Beijing.
Juniper trees in the Dulan forest grow high on the northern Tibetan plateau, at altitudes between 3,000 and 4,500 metres above sea level.
This remoteness means these trees have been minimally affected by human influence throughout their lifespans, which range from 15 to 1,967 years old.
The team performed a statistical analysis of the thickness of growth rings in 469 trees and were able to identify a set of periodic variations over short timescales.
From this they found evidence of several repeating patterns within the ring thicknesses.
Two of these, with a period of 11 and 85 years, match up with patterns found from studying changes in sunspot numbers, named the Schwabe cycle (the Solar Cycle) and Gliessberg cycle respectively.
But the researchers also found a number of other cycles with periods between 3.3 years and more than 1,000 years, with as-yet unknown causes.
The well-known Milankovitch cycles operate over timescales of tens or hundreds of thousands of years, but Courtillot and his colleagues argue that their analysis of these tree rings reveal there could be much shorter cycles varying over centuries or even years.
This is a controversial claim, and whether these shorter-timescale cycles are genuine or not will likely come out in the wash with further research.
But the statistical analysis of the growth rings of such unique, ancient trees holds great promise for better understanding our planet’s climatic history.
Courtillot describes these Tibetan junipers as “astro-geophysical observatories” – offering an intriguing link between living organisms and cosmic influences on Earth’s climate.
Lewis Dartnell was reading A Living Forest of Tibetan Juniper Trees as a New Kind of Astronomical and Geophysical Observatory by Vincent Courtillot et al. Read it online at: arxiv.org/abs/2306.11450.
This article originally appeared in the September 2023 issue of BBC Sky at Night Magazine.
