ESA’s Earth Explorer FORUM mission will provide new insight into the planet’s radiation budget and how it is controlled. Earth’s surface temperature is driven by the radiation balance at the top of the atmosphere, but this balance has been disturbed by the emission of greenhouse gases that are trapping heat in the atmosphere that would otherwise escape into space. More than half of this outgoing longwave energy is in the far-infrared part of the electromagnetic spectrum – and this has not, so far, been measured. Filling this gap, FORUM will measure across Earth’s entire far-infrared part of the electromagnetic spectrum. These measurements are important because Earth’s outgoing radiation at these wavelengths is strongly affected by water vapour and ice clouds, which in turn, play a key role in regulating surface temperatures.

credit: geoGraphics (credit: ESA/Met Office/Météo-France/geoGraphics)