UPDATE: I guess it’s GENERAL CIRCULATION Models (not “Global Climate Models”) and never again will I trust a journalist (when did I say that already… 😉 ) –
From MarsDaily (links added by me):
New analysis of data sent back by the SPICAM spectrometer on board ESA’s Mars Express spacecraft has revealed for the first time that the planet’s atmosphere is supersaturated with water vapour.
[…] descriptions of the vertical distribution of water vapour – a key factor in the study of Mars’ hydrological cycle – has generally been based upon global climate models. This gap in the data has now been addressed by the SPICAM (Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars) imaging spectrometer on Mars Express.
[…] Surprising new results [published in this week’s Science], based on SPICAM data obtained during the northern spring and summer, indicate that the vertical distribution of water vapour in the Martian atmosphere is very different from previous assumptions.
[…] Until now, it was generally assumed that such supersaturation cannot exist in the cold Martian atmosphere: any water vapour in excess of saturation was expected to be converted immediately into ice. However, the SPICAM data have revealed that supersaturation occurs frequently in the middle atmosphere – at altitudes of up to 50 km above the surface – during the aphelion season, the period when Mars is near its farthest point from the Sun.
Extremely high levels of supersaturation were found on Mars, up to 10 times greater than those found on Earth. Clearly, there is much more water vapour in the upper Martian atmosphere than anyone ever imagined. It seems that previous models have greatly underestimated the quantities of water vapour at heights of 20-50 km, with as much as 10 to 100 times more water than expected at this altitude. […]