A PIONEERING STUDY OF THE CARBON FOOTPRINT IN THE GRAND EXPERIMENT FOR DETECTING PARTICLES AND RADIATION FROM SPACE
Large-scale physics and astrophysics experiments gather a large fraction of the scientific staff and absorb a significant part of the science budget. As such, it seems essential to assess their environmental impact. IAP Intern Clarisse Aujoux (ENSTA), and researchers Kumiko Kotera (IAP) and Odile Blanchard (Université Grenoble Alpes) led a pioneering study on the Carbon footprint of the international GRAND Project, published in Astroparticle Physics and Nature Reviews Physics. This study opens the way to controlling the environmental impact of large physics and astrophysics experiments.
The Giant Radio Array for Neutrino Detection, or GRAND project, is organized and funded by institutions from 11 countries including France, China, the Netherlands, the USA, and Brazil. It aims primarily at detecting neutrinos, cosmic rays (protons or atomic nuclei) as well as gamma rays coming from space with ultra-high energies, in order to understand their astrophysical origins, which are unknown so far. The detection will be performed with a colossal array of 200,000 radio antennas over 200,000 km2 (about the size of England), split into 20 sub-arrays of approximately 10,000 km2 each, that will be deployed worldwide. The strategy of GRAND is to detect the so-called air showers above 1017 electronvolts that are induced by the interaction of the cosmic high-energy particles with the molecules in the atmosphere or the Earth crust: these interactions produce a cascade of particles and an associated electromagnetic radiation in the radio wavelength range from 50 to 200 megahertz.
Figure 1: A prototype GRAND antenna being tested at the deployment site of the 300 antenna pathfinder, GRANDProto300, in the Qinhai Province, China. Photo credit: GRAND collaboration.
A staged construction plan aiming at validating the key techniques of the array, while achieving important science goals in the physics of ultra-high energy cosmic rays, radio astronomy, and cosmology early during construction, has been adopted by the collaboration. A “pathfinder” array of 300 antenna, named GRANDProto300, is planned to be deployed in 2021 (Fig. 1). It aims at demonstrating autonomous radio detection of inclined air showers (coming from a direction close to the horizon), and make measurements of the composition and the muon content of cosmic rays at energies around 1016.5 to 1018 electronvolts. The first 10,000-antenna sub-array (GRAND10k) is planned to be deployed in the mid-2020s, and will have the sensitivity to detect the first ultra-high energy neutrinos. In its final configuration GRAND200k, planned for the 2030s, the experiment is expected to reach neutrinos flux sensitivities 100 times better than in current experiments, and to locate their astrophysical sources of emission with an angular resolution of less than a degree on the sky, therefore opening the door to ultra-high energy neutrino astronomy on the sky.
The GRAND collaboration is concerned about its environmental impact, and a “GRAND Carbon Committee” was set up. As the experiment is in its prototyping stage, it is the appropriate time to make decisions according to environmental criteria. The first step towards taking such measures is to estimate the carbon footprint of the experiment, and assess the major sources of emission. A pioneering study of the global carbon footprint assessment of the GRAND experiment was conducted by Clarisse Aujoux (Masters’ intern at the Institut d’astrophysique de Paris, student of the École Nationale Supérieure des Techniques Avancées - ENSTA), Kumiko Kotera (researcher at the Institut d’astrophysique de Paris, co-spokeperson of the GRAND collaboration), and Odile Blanchard (professor of economics at the Université Grenoble Alpes, one of the coordinators of Labos1point5).
The study they have performed focuses on the greenhouse gas emissions originating from three sources: travel, digital technologies and hardware equipment. Interestingly, it was found that these emission sources have a different impact depending on the stages of the experiment (Fig. 2 and 3). Digital technologies and travel prevail for the small-scale prototyping phase (GRANDProto300), whereas hardware equipment (material production and transportation) and data transfer and storage largely outweigh the other emission sources in the final large-scale phase (GRAND200k). In the mid-scale phase (GRAND10k), the three sources contribute nearly equally.
Figure 2: Roadmap of the GRAND project showing the different stages of the project, with information on the envisioned set-up, the staff growth of the collaboration, and the major greenhouse gas emission sources with their contribution in tCO2e/yr (total number of tons of equivalent CO2 emission per year), as well as the fractions originating from the digital, travel and hardware components of the project (source: Aujoux, Kotera & Blanchard, 2021, https://arxiv.org/pdf/2101.02049.pdf)
Figure 3: Projected distribution of greenhouse gas emissions from all sources for the planned arrays at the various stages of the GRAND project: GRANDProto300, GRAND10k and GRAND200k. The title indicates the total number of tons of equivalent CO2 emission per year due to each source at each stage of the experiment (source: Aujoux, Kotera & Blanchard, 2021, https://arxiv.org/pdf/2101.02049.pdf).
The study has initiated numerous discussions within the collaboration, as various types of actions may be implemented to mitigate the carbon footprint of GRAND, at all stages of the project deployment:
— Travel emissions may be reduced by encouraging local collaborators to perform on-site missions or by having international collaborators stay longer on the site of the experiment, rather than doing multiple trips of only a few days. Travel emission may also be reduced by optimizing the location of the meetings, limiting the number of attendees from the collaboration, opting for some virtual meetings, and combining virtual and physical meetings.
— Options to reduce emissions from digital technologies include the reduction in the volume of data to be archived. The collaboration is already developing data reduction strategies to reduce the carbon footprint of data transfer and storage by a factor of 10,000 to 100,000. It was also found that shipping regularly the disks containing the archival data by airmail would be largely less emitting than transferring the data via the internet. As for the emissions from simulations and data analysis, the challenge is to reduce the millions of computing hours expected to be spent yearly. Incentives to weigh the cost/benefit ratio of the simulation runs may contribute to lower the carbon footprint in the years to come.
— Mitigating the emissions from manufacturing and hauling the hardware equipment will be a top priority for the design of the GRAND200k phase, as these emissions are projected to weigh most of the carbon footprint in that final configuration of the project. The plans include optimizing the environmental cost of the materials used for the antennas, the solar panels and the batteries, establishing a recycling plan, and monitoring the transportation from the production sites to the antenna array sites.
This study was published in a Nature Reviews Physics article. The presented methodology is fully transparent and uses open source data, making the method replicable to any other scientific consortium. The GRAND collaboration will take several actions in response to this study. The various action plans proposed for each emission source will be documented in a GRAND “Green Policy”, which each collaboration member will be encouraged to follow, in order to reduce the collective carbon footprint of the project.
Astroparticle Physics article: Aujoux, Kotera & Blanchard, 2021, “Estimating the carbon footprint of the GRAND project, a multi-decade astrophysics experiment” https://doi.org/10.1016/j.astropartphys.2021.102587 (Public version)
Science China Physics, Mechanics & Astronomy article: Álvarez-Muñiz et al. 2020, “The Giant Radio Array for Neutrino Detection (GRAND): Science and Design” https://doi.org/10.1007/s11433-018-9385-7 (Public version)
In Astroparticle Physics European Consortium (APPEC) 2021: “Interview with Clarisse Aujoux, Kumiko Kotera and Odile Blanchard on the first carbon footprint study of an astroparticle physics experiment” https://www.appec.org/news/carbon-footprint-study-for-the-grand-project
Spiegel (in German) article 2021: “Wie klimaschädlich darf Grundlagenforschung sein?” https://www.spiegel.de/wissenschaft/mensch/grundlagenforschung-wie-klimaschaedlich-darf-sie-sein-a-86856f22-ffc9-45e0-98b2-0cda2ca67ea5
Writing and contactKumiko Kotera
Institut d’astrophysique de Paris, CNRS, Sorbonne Université
kumiko.kotera [at] iap [dot] fr
Web writing: Valérie de Lapparent
Layout and iconoraphy: Jean Mouette