This is an extraordinary reference list.
[1] The last IPCC report, which the authors apparently did not read as this article assumes climate models are the main way to estimate the climate sensitivity and the only thing they need to refute to make extraordinary claims on the climate sensitivity.
[2] Their own article in a really bad journal, which I would count as not-reviewed manuscript.
[3] Their own article in a predatory journal, which thus has manuscript status.
[4] Their own manuscript.
[5] A real scientific article the authors apparently did not read, as they applied the equation wrong.
[6] A not even public manuscript.