The Blog of the New Sun

While no one was looking the sun has gone cold, more precisely the sun godess has decreased total solar irradiation by about 4 W/m² to 1360.8 + 0.5 W/m² from 1365.4 + 1.3 W/m²

ERB is the Earth Radiation Budget instrument, ACRIM is the Active Cavity Radiometer Irradiation Monitor, SORCE is the Solar Radiation and Climate Experiment carrying the TIM, Total Irradiation Monitor.  The rest is left to the industrious reader.

What happened was that apertures in earlier instruments were not properly chosen, allowing excess light to be scattered into the sensor (right side of the figure below) resulting in higher TSI being measured.  The magnitude of the effect was determined in a purpose built testing facility at LASP.  The error is not without consequences As Kopp and Lean point out,

A nonzero average global net radiation at the top of the atmosphere is indicative of Earth’s thermal disequilibrium imposed by climate forcing. But whereas the current planetary imbalance is nominally 0.85 W/m² [Hansen et al., 2005], estimates of this quantity from space‐based measurements range from 3 to 7 W/m² SORCE/TIM’s lower TSI value reduces this discrepancy by 1 W/m²[Loeb et al., 2009]. We note that the difference between the new lower TIM value with earlier TSI measurements corresponds to an equivalent climate forcing of −0.8 W/m², which is comparable to the current energy imbalance.

 This does not directly affect the ACRIM/PMOD controversy, eg. whether there is a very slight warming of the sun over the last three solar minima, is warming by 0.003% or cooling by 0.011% or less per decade.  The effect on climate models remains an open question.  If anyone has more on this, please let Eli know.

UPDATE:6/2/2103 Showing the new solar irradiance series from Kopp and Lean