FEEDBACK FORMULISM borrowed from control theory is universally misapplied in deriving climate sensitivity. Though in electronic feedback amplifiers the DC input is often small enough to be ignored without error, in climate the overwhelmingly predominant emission temperature must not be, but was hitherto, omitted from the input to the temperature-feedback loop. In effect, its large feedback response was added to (and miscounted as part of) the actually small feedback response to anthropogenic warming. By that grave control-theoretic error, feedback response was hitherto thought to constitute as much as 2 {1 to 4] K, or 67% [50% to 80%], of the long-projected 3 [2 to 5] K equilibrium doubled-CO2 sensitivity (ECS). However, at the 1850 equilibrium, feedback response comprised only 7.7% of global temperature, implying only 1.2 K ECS. Allowing for subsequent time-variance, a feedback factor 0.09 would yield 2 K ECS, while 0.10 would yield 5 K: but no precision so fine as 0.01 is attainable, vitiating all ECS projections via feedback formulism, hitherto the standard method. After correcting the error, mitigation is unnecessary.