Does UAH Have a Cool Bias?

By the way, there is a claim literature that UAH's mid-tropospheric temperatures are biased cool:

Po-Chedley, Stephen, Qiang Fu, 2012: A Bias in the Midtropospheric Channel Warm Target Factor on the NOAA-9 Microwave Sounding Unit, J. Atmos. Oceanic Technol., 29, 646–652.

whose abstract says:

"The analysis reveals that the UAH TMT product has a positive bias of 0.051 ± 0.031 in the warm target factor that artificially reduces the global TMT trend by 0.042 K decade⁻¹ for 1979–2009. Accounting for this bias increases the global UAH TMT trend from 0.038 to 0.080 K decade⁻¹, effectively eliminating the trend difference between UAH and RSS and decreasing the trend difference between UAH and NOAA by 47%."

That would essentially eliminate the RSS-UAH discrepency I pointed out. (Actually I noted this paper last year, but forgot about it until I read this HotWhopper post.)

(Why is it UAH's biases always seem to be on the cool side??)

This claim prompted a response by Christy and Spencer, which brought its own response from the original authors last month, saying

The main finding by Po-Chedley and Fu was that the University of Alabama in Huntsville (UAH) microwave sounding unit (MSU) product has a bias in its NOAA-9 midtropospheric channel (TMT) warm target factor, which leads to a cold bias in the TMT trend. This reply demonstrates that the central arguments by Christy and Spencer to challenge Po-Chedley and Fu do not stand.

Obviously this correction, if indeed true, would bring UAH into agreement with RSS but not with the model results as claimed by Spencer. I am still puzzled how it is that the average model trend doubled from 2007 to 2013.