How then is "climatic forcing," actually calculated.
Does it involve direct measurement of atmospheric phenomena?
..
The answer is yes, Forcings are directly measured in the atmosphere.
http://www.arm.gov/instruments/instrument.php?id=aeri
Atmospheric Radiation Measurement Program Instruments
http://www.arm.gov/instruments/instclass.php?id=radio
We also look down from the top: for instance, instruments like
CERES, IRIS, ERBE, and HIRS.