A comprehensive assessment of the carbon footprint of an astronomical institute

Table 1 presents our estimates of IRAP’s GHG emission by source, while Fig. 1 provides a graphical representation of the data. In total, we estimate that IRAP had a carbon footprint of approximately 7,400 ± 900 tCO₂e in 2019. About 60% of the footprint is attributed to the use of observational data from space missions and ground-based observatories, and the use of these infrastructures is clearly the primary source of IRAP’s GHG emissions. The second major contributor (18% of emissions) is related to the purchase of goods and services, of which an estimated 85–90% is attributed to the instrument development projects undertaken at IRAP. Professional travel amounts to 16% of IRAP’s carbon footprint, of which 96% is due to air travel. The latter source is very unevenly distributed across the staff, with 20% (50%) of the emissions being attributable to 12 (48) people, out of a total of about 260 employees. Interestingly, there is a very limited effect of seniority in this distribution: the fraction of the staff responsible for 20% (50%) of the emissions has an average age of 46.9 yr (47.3 yr), to be compared with an average of 44.3 yr for the whole staff. There seems to be a much more pronounced effect of gender: 92% (87%) of the persons responsible for 20% (50%) of the emissions are male, to be compared with an average for the whole staff of 75%. Finally, there is a non-negligible fraction of engineers and technicians among the people responsible for most of the GHG emissions from professional travel, and they are primarily involved in the development of future space missions, demonstrating that this activity is an important driver of travel-related emissions at IRAP.

A graphical representation of Table 1.

Our results clearly point to the main driver of IRAP’s carbon footprint: astronomical research infrastructures. In total, use of data from astronomical facilities and the purchase of goods and services for instrument development account for about 70% of IRAP’s carbon footprint. This is a considerable contribution, and one omitted in previous estimates of the carbon footprint of astronomical institutes. In addition, it is likely that a significant fraction of professional trips at IRAP are also connected to instrument development projects, which only strengthens this conclusion.

Whether such a repartition can be considered as generic for the astronomy community remains to be confirmed by performing comprehensive carbon footprint assessments at other institutes. IRAP has a long history in instrument development and observational data analysis that is no doubt reflected in the present result, which already exhibits interesting similarities and differences to other published assessments. At IRAP, flights account for 8.1 tCO₂e per researcher with a PhD degree, which is comparable to the estimates of 8.5 tCO₂e being found for MPIA and 12.0 tCO₂e for the Australian community⁶, but much larger than the 2.0 tCO₂e per researcher for the Dutch community⁸. Conversely, the emissions from supercomputing at IRAP amount to 0.2 tCO₂e yr^–1 per researcher, on average, which covers the impact from electricity consumption, equipment, and operations of the computing centres; at MPIA, supercomputing generates an average 4.6 tCO₂e yr^–1 per researcher, from electricity consumption only. Only a small part of the difference can be explained by the carbon intensity of electricity, which is a factor ∼4 higher at MPIA with respect to IRAP.

An important factor affecting the final repartition of GHG emissions is that the operation of local infrastructure — heating, electricity, commuting, food, waste and so on — makes a relatively small contribution of about 800 tCO₂e yr⁻¹ to IRAP’s carbon footprint. The energy sources from which electricity and heating are produced have a relatively low carbon footprint, with electricity being predominantly of nuclear origin in France and heating of our largest building arising from biomass burning, with related emission factors being 60–70 gCO₂e kWh⁻¹. Assuming a worst-case carbon intensity of ∼800 gCO₂e kWh⁻¹ instead — representative of countries like Australia, Poland, China, India, or South Africa — the related sources would increase to about 2,700 tCO₂e yr⁻¹, comparable to the sum of professional travels and purchase of goods and services at IRAP. A higher carbon intensity of electricity would also affect other sources such as external computing, and to some extent the purchase of goods and services. If IRAP were situated in a country that relies significantly on fossil fuels for electricity production and heating, we estimate that our total 2019 footprint would be at least 10,000 tCO₂e.