# Non-linear feedbacks ...and Then There's Physics

I thought I would just briefly mention a recent paper by Bloch-Johnson, Pierrehumbert & Abbot called Feedback temperature dependence determines the risk of high warming. As I understand it, the basic idea is to consider what would happen if the feedback response has a temperature dependence. If the feedback response is linear, then you can estimate the climate sensitivity, \$latex lambda\$, at any time using

\$latex lambda = -dfrac{Delta F}{Delta T}.\$ Credit : Figure 1 from Bloch-Johnson et al. (2015) However, it is clear that feedbacks do have a temperature dependence. The Planck response (\$latex dF = 4 epsilon sigma T^3 dT\$) is clearly temperature dependent. What we don’t know – given all the feedbacks – is the strength of this possible non-linearity. What Bloch-Johnson et al. do is simply assume that the climate sensitivity has a non-linear term,

\$latex -Delta F = lambda Delta T + alpha Delta…

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