Introduction
The Earth’s climate is ever changing on various time scales. Most recently anthropogenic climate change has become the dominating driver for climate trends. However, natural drivers have modulated Earth’s climate in the past and continue to play a role today and into the future. While stable, long-term drivers lastingly alter climate, episodic events can modulate regional and global climate on short time scales of years to decades. Two prominent examples of such events are volcanic and solar eruptions. While there are limited direct observations of such events, due to their sporadic nature, knowledge about their occurrence in the past can be inferred from proxies for various climate variables.
The project
“Volcanic and solar particle events in the past: Atmospheric Effects and cOsmogenic Nuclides in ice cores” (AEON) is a project carried out by the two partnering institutes CEREGE in France and PMOD/WRC in Switzerland. The aim of the AEON project is to reconcile observations and theoretical understanding of the two natural climate forcings: volcanic activity and solar variability. Eruptions of both volcanic and solar nature (also called solar superflares) may - besides the anthropogenic forcing - play an important role in today’s climate and strong events can be hazardous for humans and modern technology (e.g. satellites, planes). In the past, these forcings have not been modelled in full complexity, i.e. with all involved Earth system components being interactive in models and have been poorly constrained. For volcanic eruptions, detailed records spanning over the past millennia exist and can be used to force models. A complete record of solar superflares in the same time period, conversely, does not yet exist. In the scope of this project, new, high-precision observational data will be extracted from isotope measurements in ice cores. CEREGE is especially well equipped to measure the new, promising Chlorine-36/Beryllium-10 ratio proxy, which allows the reconstruction of solar superflare energy spectra. All these data will then be used to simulate volcanic and solar eruptions in the state-of-the-art atmosphere-ocean-aerosol-chemistry-climate model SOCOLv4. Both the volcanic and cosmogenic particles enter the atmosphere after being produced, but ultimately leave their fingerprints in various locations on the surface, especially in the remote ice shields. Therefore, the entire physical and chemical evolution of the particles in the atmosphere contributes to the signal found in the records. Thus, to perform useful simulations, we will further develop the model to include relevant chemical reactions and microphysical processes, alongside the already well described detailed atmospheric transport. Notably, cosmogenic nuclides interact with aerosol particles and may be scavenged and deposited. When the atmospheric aerosol is enhanced after a volcanic eruption, interactions between volcanic and cosmogenic particles may leave their own fingerprint in the record. This effect would need to be accounted for in proxy interpretation. Ultimately, this work will allow for a more sophisticated analysis of atmospheric and climate effects of volcanic eruptions and solar variability compared to previous work.
My role in the project
For my doctoral thesis, I will run SOCOLv4 and analyse the data produced in the various simulations. Mainly I will focus on the volcanic and solar impacts on the atmosphere and climate, and the interactions between volcanic aerosol particles and cosmogenic nuclides. Within the atmosphere, I will give special attention to stratospheric chemistry and circulation, stratosphere/troposphere coupling and tropospheric circulation. While we are obviously interested in the troposphere because we live in it and weather takes place here as well, it is itself strongly connected to the stratosphere above and reacts to changes therein. Also, the stratosphere contains the ozone layer, which is vital to life on Earth and can react strongly to volcanic eruptions.
Quiz question
What is the main constituent of the stratospheric aerosol layer?
Sulfate particles
Black Carbon (BC) from human emissions
Isotopes from Galactic Cosmic Rays (GCR)