The imperative to reduce carbon emissions in astronomy

For astronomers to make a significant contribution to the reduction of climate change-inducing greenhouse gas emissions, we first must quantify the sources of our emissions and review the most effective approaches for reducing them. Here we estimate that Australian astronomers' total greenhouse gas emissions from their regular work activities are ≳25 ktCO₂e yr^-1 (equivalent kilotonnes of carbon dioxide per year). This can be broken into ~15 ktCO₂e yr^-1 from supercomputer usage, ~4.2 ktCO₂e yr^-1 from flights (where individuals' flight emissions correlate with seniority), >3.3 ktCO₂e yr^-1 from the operation of observatories, and 2.6 ± 0.4 ktCO₂e yr^-1 from powering office buildings. Split across faculty scientists, postdoctoral researchers and PhD students, this averages to ≳37 tCO₂e yr^-1 per astronomer, more than 40% greater than the average Australian non-dependant's emissions in total, and equivalent to around five times the global average. To combat these environmentally unsustainable practices, we suggest that astronomers should strongly preference the use of supercomputers, observatories and office spaces that are predominantly powered by renewable energy sources. Where current facilities do not meet this requirement, their funders should be lobbied to invest in renewables, such as solar or wind farms. Air travel should also be reduced wherever possible, replaced primarily by video conferencing, which should also promote inclusivity.