A team led by Alan Cooper found a detailed record of the Laschamp excursion about 41,000 years ago from the rings of New Zealand swamp kauri trees. The record reveals a substantial increase in the carbon-14 content of the atmosphere during the period of weakening magnetic field strength preceding the polarity switch.
With this evidence they concluded that the geomagnetic field minimum caused significant changes in atmospheric ozone concentration that drove synchronous global climate and environmental shifts.
Over the past 170 years, the Earth’s magnetic field has steadily weakened by about 9% and because of this and the current rapid movement of the magnetic North Pole, many believe that a field reversal may be imminent. Such a reversal would result in increased exposure to extreme solar storms, with multibillion dollar daily loss estimates for the economy. Sedimentary and volcanic records of the Laschamp excursion indicate a weakening of the magnetic field intensity to less than 28% of current levels during the reversed phase and as little as 0 to 6% during the preceding transition as polarity switched.
The current view is that there is no relationship between geomagnetic reversals and climate or environmental changes. This is based on studies of Greenland ice cores which have failed to reveal notable impacts in high-latitude paleoclimate associated with Laschamps and other reversals. However, the substantial increase levels of solar and cosmic radiation reaching the Earth’s atmosphere because of the weakened geomagnetic field are likely to have increased atmospheric ionization and decreased stratospheric ozone levels. This has the potential to generate regional climatic impacts, particularly in lower latitudes.
Voosen, P. (2021). Kauri trees mark magnetic flip 42,000 years ago. Science, 371(6531), 766. https://science.sciencemag.org/content/371/6531/811