Authors: Jürgen Knödlseder, Sylvie Brau-Nogué, Mickael Coriat, Philippe Garnier, Annie Hughes, Pierrick Martin, and Luigi Tibaldo
First Author’s Institution: Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
Status: Published in Nature Astronomy
There is no doubt that telescopes are integral to astronomy. For example, my research relies entirely on observations from the Hubble Space Telescope (HST) and the Magellan Telescope in the Chilean Atacama Desert. However, most astronomers, including myself, have never considered the detrimental environmental effects of constructing and operating the hundreds of telescopes around the world.
While recent attention has focused on the environmental impacts in astronomy of switching to virtual conferences or the use of supercomputers, today’s paper measured the environmental impact, or carbon footprint, of constructing and operating ground-based and space-based telescopes. Our carbon footprint is a common measure for how much carbon dioxide (CO2) we release into the Earth’s atmosphere. In summary, the authors found the approximate annual carbon footprint was 525,000 tons of CO2 for space-based missions and 757,000 tons of CO2 for ground-based missions. The combined total of 1,282,000 tons per year is about the annual carbon footprint of the entire African country, Sierra Leone. Dividing this annual carbon footprint by 30,000 astronomers (the author’s estimate of the number of astronomers with a PhD) gives an annual carbon footprint of 37 tons of CO2 per astronomer. For comparison, the average carbon footprint for an American is 16 tons (globally, the average is closer to 4 tons). The authors found that this average annual footprint due to observatories is larger than other well-studied sources of emissions, like from flying for conferences (8.5 tons/astronomer), electricity use (5.2 tons/astronomer), and supercomputing (22 tons/astronomer).
The authors of today’s paper analyzed space-based missions (e.g., HST, Chandra, Kepler) and ground-based missions (e.g., VLT, ALMA, CFHT) separately.
Carbon Footprint of Space-based Missions
The HST (Figure 1) was the first to accurately measure the age of the universe, detect exoplanet atmospheres, and determine the origin of gamma ray bursts. Furthermore, with 52,497 papers written by 43,315 unique authors, the HST has been unmatched as a telescope in its impact on astronomy. However, the HST also has contributed at least 555,500 tons of CO2 in its 30-year lifetime. This begs the question: what is the environmental cost to Earth of observing the Universe?
To estimate the carbon footprint of space-based observatories, the author used two different methods: “cost based emission” and “mass based emission.” In the “cost based emission” method, the authors determined that it takes approximately 140 tons of CO2 per million € (M€) of mission cost for an average space-based telescope. They multiplied this number by the total cost of each mission to determine the carbon footprint of a given mission. For example, the HST has cost 8,037 M€ over its lifetime. Multiplying (8,037 M€) ✕ (140 tons of CO2 / M€) = 1,125 kT of total CO2 in its lifetime. Similarly, in the “mass based emission” method, the authors determined it takes approximately 50 tons of CO2 per kg of payload launch mass to launch an observatory. They then multiplied this number by the mission’s launch mass to determine the total carbon footprint. For example, the HST required 11,110 kg of payload launch mass. Multiplying (11,110 kg) ✕ (50 tons of CO2 / kg) = 555 kT of total CO2 in its lifetime. The authors found that the cost-based estimates were on average about 20% larger than the mass-based estimates, likely because mission complexity is not taken into account in the mass-based estimates. For example, the HST has had five Space Shuttle servicing missions that would be included in the cost-based estimate but not in the mass-based estimate.
Carbon Footprint of Ground-based Missions
To estimate the emission of ground-based observatories, the authors first determined that it takes approximately 250 tons of CO2 for every million € it costs to operate an observatory, and 240 tons of CO2 for every million € it costs to construct an observatory. They then multiplied these two numbers by the observatory’s annual operating costs and construction costs, respectively, to determine the total “cost-based emission.” For example, the VLT cost 1,384 M€ to construct and 40 M€/year to operate. This gives (1,384 M€ ✕ 240 tons of CO2/M€) + (40 M€/year ✕ 21 years ✕ 250 tons of CO2/M€) = 540 kT of total CO2 in its lifetime.
The construction of ground-based observatories often requires high quantities of concrete and steel, which both have incredibly high carbon footprints (the cement industry is responsible for 8% of the global greenhouse gas emissions!). Electricity and energy consumption of ground-based observatories also takes an environmental toll. Chile’s Atacama Desert is home to 16 observatories, including the VLT, ALMA, and the Atacama Cosmology Telescope (ACT). While Chile’s dry air makes it an exceptional location for observing, Chile ranks only in the middle of countries when it comes to the cleanliness of its electricity grid. “Chile has a kind of average emission factor for electricity,” said Knödlseder, the lead author of the paper at a news conference for this paper announcing the results. “So it’s not as high, for example, as Australia, which burns a lot of coal, but it’s not as low as Sweden and France, which use a lot of renewable energy.” Switching the main power source of telescopes in the Atacama Desert to solar energy, which Chile’s desert has in abundance, would help ground-based telescopes operate with fewer carbon emissions.
The carbon footprints for the 46 space-based telescopes and 39 ground-based telescopes studied in this paper were then extrapolated to estimate the total carbon footprint of all space-based and ground-based telescopes in the world using a boot-strap sampling method. This means randomly selecting (with replacement) N carbon footprints from the observatories in their list, where N is the total number of observatories in the world. The authors performed this simulation 10,000 times and computed the mean and standard deviation of all estimates to assess the carbon footprint of all observatories and its uncertainty.
Suggestions for the Future
The authors calculated that to reach net-zero Greenhouse Gas (GHG) emissions in the future, an astronomer’s footprint (including all their activities outside of work) must be reduced to 2 tons of CO2 per year. Thus, emissions of observatories must be reduced by at least a factor of 20. At the end of the paper, they lay out four main suggestions to decrease the carbon footprint of astronomy observatories.
- All planned facilities should assess their projected carbon footprint and make their results public. Furthermore, funding agencies could require that facilities conduct and publish such analyses. With more accurate data, studies such as this one could make more robust and specific conclusions. For example, the James Webb Space Telescope (JWST) is predicted to have a total carbon footprint between 310,000 and 1,223,000 tons of CO2, which is comparable to the current largest footprints estimated in this study. It is imperative that facilities such as JWST consolidate these estimates and implement effective measures to reduce their carbon footprints.
- All existing facilities should prepare an action plan for how to reduce their footprints over the coming years. Progress should also be made completely transparent to the public so that facilities can be held accountable
- Funding agencies should include carbon budget limits. The environment should begin informing decisions about implementation and funding.
- Slow Science movement: Finally, the authors argue that reducing the pace at which we are building new astronomical observatories is the only measure that can make our field sustainable in the short run. While this does not mean we must completely stop developing new observatories, we must do it at a considerably slower rate. Once the economy is substantially decarbonized, the rate of construction of new observatories could be increased. Reducing the pace of science has other ancillary benefits to combating climate change; for example, the Slow Science movement advocates for a more comprehensive exploitation of data, less publication pressure, and more money available to move the already existing observatories towards sustainability. While the prospect of “slowing down” might not be a popular one among astronomers and scientists, it is paramount that our foremost priority be stopping climate change and reducing our emissions.
Astrobite edited by Sabina Sagynbayeva
Featured image credit: NASA