Cosmic rays from supernovae can influence Earth’s cloud cover and thereby climate according to new research from a team from Denmark.
The study reveals how atmospheric ions, produced by the energetic cosmic rays raining down through the atmosphere, helps the growth and formation of cloud condensation nuclei – the seeds necessary for forming clouds in the atmosphere. When the ionization in the atmosphere changes, the number of cloud condensation nuclei changes, affecting the properties of clouds.
It is thought the role of cosmic rays could be significant for our understanding of why climate has varied in the past and how future climate changes could evolve. “Finally we have the last piece of the puzzle explaining how particles from space affect climate on Earth. It gives an understanding of how changes caused by Solar activity or by super nova activity can change climate,” said Henrik Svensmark, from DTU Space at the Technical University of Denmark, and lead author of the new study.
Cloud condensation nuclei can be formed by the growth of small molecular clusters called aerosols. It has until now been assumed that additional small aerosols would not grow and become cloud condensation nuclei, since no mechanism was known to achieve this.
The new results reveal, both theoretically and experimentally, how interactions between ions and aerosols can accelerate the growth by adding material to the small aerosols and thereby help them survive to become cloud condensation nuclei. It gives a physical foundation to the large body of empirical evidence showing that Solar activity plays a role in variations in Earth’s climate. For example, the Medieval Warm Period around year 1000 AD and the cold period in the Little Ice Age 1300-1900 AD fits with changes in Solar activity.
Even at low ionization levels about 5% of the growth rate of aerosols is due to ions. In the case of a nearby supernova the effect can be more than 50% of the growth rate, which will have an impact on the clouds and the Earth’s temperature.