  The mid-infrared spectral region provides a unique window into the
atmospheric temperature, chemistry, and dynamics of the giant planets. From
more than a century of mid-infrared remote sensing, progressively clearer
pictures of the composition and thermal structure of these atmospheres have
emerged, along with a greater insight into the processes that shape them. Our
knowledge of Jupiter and Saturn has benefitted from their proximity and
relatively warm temperatures, while the details of colder and more distant
Uranus and Neptune are limited, as these planets remain challenging targets. As
the timeline of observations continues to grow, an understanding of the
temporal and seasonal variability of the giant planets is beginning to develop,
with promising new observations on the horizon.
