Not a rebuttal, however the contrail effect is estimated at
57.4 out of a total 100.9 mW m−2.
But their estimated uncertainty range is actually somewhere between 17 and 98.
Furthermore, they have made a few of statements indicating how “uncertain” they are about their “uncertainty range”. Basically, there is very little data to support their model. For example, in Appendix E:
The statistical uncertainty of global contrail cirrus RF cannot be estimated from the small number of available studies. Uncertainties affecting our contrail cirrus estimates are, on the one hand, due to (A) uncertainties in the radiative response to the presence of contrail cirrus and, on the other hand, (B) uncertainties in the upper tropospheric water budget and the contrail cirrus scheme. In most cases, we can only infer very rough estimates for the uncertainties related to specific processes.