The Need for MERBE
Humans have raised atmospheric CO2 by as much in the last 100 yrs as it would naturally take 10's of thousands of yrs to happen. What we need to know is how will the climate change in response to an un-precedented recent rate of anthropogenic Green House effect forcing increase. To find out we must validate & prove computer simulations run up to the present, based on satellite observations, giving confidence in their global warming predictions. However since such official NASA records are only a few decades old and with non-perfect calibration, it was concluded by the 2007 NRC Decadal Survey that:
"the single most critical issue for current climate change observations was their lack of accuracy and low confidence in observing the small climate change signals over long decade time scales" .
The short animation above shows that humans have increased atmospheric CO2 levels in only 100 yrs by an amount that would naturally take many 1000's of yrs to occur.
Is it the Earth or your Instrument changing?
Entering Short Wave (SW 0.2-5µm) light from the Sun and Long Wave (LW 5-200µm) Infra-Red sent back to space are part of the Earth Radiation Budget (ERB), the energy in/out of a planetary heat engine, from which the work done drives all weather and climate.
Earth's weather/climate system is driven by incoming solar or SW light and outgoing infra-red or LW radiance. (Fig by H. E. Brindley)
Space shuttle mission STS-32 in 1990 retrieved ERB instruments from orbit as part of the Long Duration Exposure Facility (LDEF) mission, showing extreme degradation of optics in ultra-violet (UV) due to contamination.
To understand and simulate Earth's climate system requires satellite measurements of ERB SW & LW fluxes using satellites in orbit. ERB fluxes have been measured by various USA/European/Asian instruments, however such continuous results are only two decades old . This is challenging because such ERB telescopes are known to change once in space, in ways we cannot currently detect, as shown by the Long Duration Exposure Facility (LDEF) mission (which retrieved a spare Nimbus 7 ERB device from low Earth orbit using the space shuttle as shown in the movie). Post shuttle retrieval analysis of LDEF ERB optics showed that they drop in transmission of Ultra-Violet (UV) light relative to the visible due to contamination, as shown below left. Such a device would therefore incorrectly measure a false drop in Earth solar albedo due to un-tracked loss of UV responsivity (below middle graph).
LDEF ERB optics showed significant UV degradation
LDEF UV degradation would incorrectly lower CERES SW
CERES on-board lamps cannot diagnose UV degradation
CERES hence has no built-in way to track such large changes to its optics in the UV region because its lamp output (above right), has no energy there. Until 2005 such CERES devices were operated in Rotating Azimuth Plane (RAPs) modes where it was later discovered that baffle contaminants would move
to telescope optical surfaces, mobilized by atomic oxygen, when they were facing in the satellite direction of travel or ram direction (see CERES instrument animation). Based on the results of LDEF, a physical contamination model was developed that determined the changes to ERB telescope spectral response (referred to as "Spectral Darkening").
CERES optics suffered LDEF-like contamination due to exposure to RAM direction when operating in RAPs/AlongTrack mode.
Note that NASA CERES have not corrected the well known false -0.5%/decade trend in their SW fluxes, which could suggest up to half of global warminig is due to the Sun, as shown below: