To reduce our astronomy-related GHG emissions, we need to identify which measures will be effective and require implementation at which level, that is, at the level of the individual researchers, the MPIA, the Max Planck Society, the astronomical community, or human society in general. Each institute will face its specific challenges. For example, we have identified the high carbon intensity of MPIA’s heating, which needs to be addressed at the institute level, but other measures need changes across the astronomical community. Measures and responsibilities can only be identified once the GHG emissions have been quantified.


Flight-related GHG emissions dominate the MPIA’s total emissions. Since there is no technology on the horizon that would reduce flight emissions to anything approaching carbon-neutral by 2050, much less 2030, the only way to reduce flight-related emissions is to reduce this form of travel. To do so, we need to identify the destinations and reasons for the air travel.

In Fig. 2, we break down the MPIA’s emissions by destination. A negligible fraction of emissions originates from flights inside Germany, and only 9% from flights with destinations inside Europe (including the Canary Islands). Though small, this European component can be further reduced by replacing air travel with train travel7. Changes to the German public servant’s travel law in early 2020 ensure that train trips to well-connected European destinations are now reimbursed, even if they are more expensive than a flight18. Moreover, at the individual level, many German researchers have pledged not to fly distances under 1,000 km19. However, the vast majority of the MPIA’s flight emissions (>90%) stem from intercontinental flights, which are dominated by destinations in the United States and Chile. Although we cannot identify the reason for each flight, in general, these international flights are a mix of travel for observation campaigns, instrument commissioning, conferences, seminars, and research visits. To reduce our flight-related emissions, we must identify solutions that enable us to reach the scientific goals of these trips without the need for air travel. The onus here is on the entire astronomical community to change how we work.

Fig. 2: Relative GHG emissions broken down by flight destination for MPIA employees.

Intercontinental flights that cannot be easily replaced by alternative means of transport make up about 91% of flying emissions. This is due to the number of flights, and the high climate impact of each intercontinental flight, primarily due to distance traversed, but also due to greater time-averaged emission altitude, for example, for nitrogen oxides.

Travel for meetings, conferences and collaborations made up a significant fraction of the MPIA’s 2018 flights, as will be the case for most astronomical institutes. At that time, video-based alternatives were only used in specific settings. However, the need to continue working during the 2020 COVID-19 pandemic resulted in the substitution of many physical meetings with virtual ones. To reduce our carbon footprint to anything approaching net zero by 2050, the expertise in hosting virtual events that was so rapidly developed during the last few months should continue to be applied and expanded. To this end, the recommendations of Klöwer et al.20 are an excellent starting point. They provide an in-depth analysis of conferencing carbon emissions and an overview of options. Their analysis shows that GHG emissions for in-person meetings will strongly depend on the meeting location relative to the origin of the participants, and they make cases, for example, for fully online meetings and hybrid models with continental in-person meeting ‘hubs’, combined with online connections between hubs, as well as other changes that would drastically reduce the conference-induced emissions. These and other models in combination with a drastically lower number of conferences promise to be an effective measure.

In contrast, we identify reasons for flights for which we have no immediate alternatives. These include, for example, extended in-person collaborative visits, which prove very effective for initiating new projects, and the installation or commissioning of instruments at telescopes including the Large Binocular Telescope (Arizona) or the European Southen Observatory Very Large Telescope (Chile). Hardware built by the MPIA must be mounted at a telescope site, tuned, and put into science operations, and as a result, expert engineers and astronomers have to be physically present for a larger number of commissioning runs. Hypothetically, some runs could be combined, but this immediately impacts engineering timescales and family boundary conditions that might be complex to solve. The institute and the astronomy community have to search for measures to address these cases, which at this point are unsolved.

Computing-related emissions

The second major contributor to the MPIA’s GHG emissions resulted from the electricity production needed for our computing resources — estimated to be 75–90% of our electricity consumption — particularly our use of supercomputing facilities. Since large-scale simulations will continue to be an important part of astrophysics in future decades, we need to identify effective measures to reduce the associated emissions. Note that we did not assess the emissions associated with the manufacture of cluster hardware, only of their use.

As is evident from the MPIA/Australian comparison of computing-related emissions, the source of electricity generation has the greatest impact on the computing-related carbon footprint. Thus, it is imperative that supercomputing facilities be run with renewable energy, and that the electricity required for cooling is minimized. The sources of national/regional energy production are decided at a political level, but the astronomical community, and indeed individual citizens, can collectively campaign for this change. As a mid-term option, supercomputing facilities could be moved to locations where renewables are available and less electrical energy is needed for cooling, for example, to Iceland, which had an average of 0.028 kg CO2e kWh–1 emission21 for produced electricity in August 2020. Additionally, potential idle times, and hence the required amount of hardware, could be reduced by switching to more cloud computing, because there capacity utilization is generally higher than for local computers22. As a community, we should guarantee an efficient use of supercomputing resources. This applies to code efficiency23 as well as to the computing architecture that we build up or rent24. All these options will require changes at the institutional and astronomy-community level.

Heating and local energy production

Finally, we briefly touch on the MPIA’s buildings. The use of oil for heating at 446 tCO2e is the third-largest contributor to the MPIA’s GHG emissions. Oil has been used since the institute’s buildings were inaugurated in 1976, due to their distance from the city’s district heating and gas network. For the future, the only viable and sustainable option for heating the institute is to use ground heat, in combination with an electrically operated heat pump. This type of heating system is already employed at the House of Astronomy, the astronomy education and outreach centre built on the MPIA campus in 2011. Not only can this heating system save 50% of energy compared to oil-/gas-based systems, but it can also be run carbon-neutral on renewable electricity. Installation of such a heating system can, in principle, be implemented at the institute level, as can improvements to building insulation, which reduce the heating needs. These changes have been proposed for the MPIA and are currently under review.

MPIA’s electricity is consumed both on campus for a mix of computing (including cooling), workshops, cleanrooms, and general office consumption, and to a large part in external high-performance computing centres, as described above. While the associated carbon emissions will decrease along with Germany’s decreasing use of coal and gas for electricity generation, this process will take a long time. We note that the MPIA’s utility contracts have a carbon intensity about half that of the German average, and in principle, for a relatively small extra cost, these contracts could be changed to provide 100% renewable electricity. However, many such contracts would not actually lead to more renewable energy being produced, but instead only formally redistribute renewable electricity volumes or emission certificates between contracts. Thus, in reality other measures would have a greater impact. We proposed a photovoltaic installation on MPIA’s roof, also currently under review, which would initially produce ~10% of MPIA’s on-campus electricity consumption at zero additional cost.

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