Title: The carbon footprint of astronomical research infrastructures

Abstract: We estimate the carbon footprint of astronomical research infrastructures, including space telescopes and probes and ground-based observatories. Our analysis suggests annual greenhouse gas emissions of $1.2\pm0.2$ MtCO$_2$e yr$^{-1}$ due to construction and operation of the world-fleet of astronomical observatories, corresponding to a carbon footprint of 36.6$\pm$14.0 tCO$_2$e per year and average astronomer. We show that decarbonising astronomical facilities is compromised by the continuous deployment of new facilities, suggesting that a significant reduction in the deployment pace of new facilities is needed to reduce the carbon footprint of astronomy. We propose measures that would bring astronomical activities more in line with the imperative to reduce the carbon footprint of all human activities.