The carbon footprint of proposed $${\mathrm{e}}^+{\mathrm{e}}^-$$ Higgs factories

Abstract The energy consumption of any the $${\mathrm{e}}^+{\mathrm{e}}^-$$ e + - Higgs factory projects that can credibly operate immediately after end LHC, namely three linear colliders (CLIC, operating at $$\sqrt{s}\,=\,380$$ s = 380 GeV; and ILC $${\mathrm{C}}^3$$ C 3 , $$\sqrt{s}\,=\,250$$ 250 GeV) two circular (CEPC FCC-ee, $$\sqrt{s}\,=\,240$$ 240 GeV), will be everything but negligible. Future boson studies may therefore have a significant environmental impact. This note proposes to include carbon footprint for given physics performance as top-level gauge design optimisation and, eventually, choice future facility. projected footprints per produced, evaluated using 2021 emission available electricity, are found vary by factor 100 depending on considered project.