It may be more efficient but how can they test that?

According to the article this is what they did:

"In research published this week in the journal Remote Sensing, Spencer and UA Huntsville's Dr. Danny Braswell compared what a half dozen climate models say the atmosphere should do to satellite data showing what the atmosphere actually did during the 18 months before and after warming events between 2000 and 2011."

"The satellite observations suggest there is much more energy lost to space during and after warming than the climate models show," Spencer said. "There is a huge discrepancy between the data and the forecasts that is especially big over the oceans."

As far as I know the DSCOVR spacecraft has not been launched yet. That's the one denied launch during the Bush administration that is ready to test earth's radiation budget.

Yes, I agree, however Bush hasn't been president for more than three years now. What's the hold-up?

But, is there a eutectic point such that the heat capacity of the atmosphere becomes more, not less, opaque to heat.

You lost me at "eutectic point".  I have no idea what-so-ever, but it sounds highly speculative to me.