  Atmospheric pollutants such as CFCs and NO$_{2}$ have been proposed as
potential remotely detectable atmospheric technosignature gases. Here we
investigate the potential for artificial greenhouse gases including CF$_{4}$,
C$_{2}$F$_{6}$, C$_{3}$F$_{8}$, SF$_{6}$, and NF$_{3}$ to generate detectable
atmospheric signatures. In contrast to passive incidental byproducts of
industrial processes, artificial greenhouse gases would represent an
intentional effort to change the climate of a planet with long-lived, low
toxicity gases and would possess low false positive potential. An
extraterrestrial civilization may be motivated to undertake such an effort to
arrest a predicted snowball state on their home world or to terraform an
otherwise uninhabitable terrestrial planet within their system. Because
artificial greenhouse gases strongly absorb in the thermal mid-infrared window
of temperate atmospheres, a terraformed planet will logically possess strong
absorption features from these gases at mid-IR wavelengths ($\sim$8-12 $\mu$m),
possibly accompanied by diagnostic features in the near-IR. As a proof of
concept, we calculate the needed observation time to detect 1 [10](100) ppm of
C$_{2}$F$_{6}$/C$_{3}$F$_{8}$/SF$_{6}$ on TRAPPIST-1f with JWST MIRI/LRS and
NIRSpec. We find that a combination of 1[10](100) ppm each of C$_{2}$F$_{6}$,
C$_{3}$F$_{8}$, and SF$_{6}$ can be detected with an S/N $\geq$ 5 in as few as
25[10](5) transits with MIRI/LRS. We further explore mid-infrared
direct-imaging scenarios with the LIFE mission concept and find these gases are
more detectable than standard biosignatures at these concentrations.
Consequently, artificial greenhouse gases can be readily detected (or excluded)
during normal planetary characterization observations with no additional
overhead.
