its not an ad hom
The thing is Roy Spencer has appealed to having investigated the subject of evolution in detail scientifically:
"Twenty years ago, as a PhD scientist, I intensely studied the evolution versus intelligent design controversy for about two years. And finally, despite my previous acceptance of evolutionary theory as "fact," I came to the realization that intelligent design, as a theory of origins, is no more religious, and no less scientific, than evolutionism."
Something is wrong if you proclaim to have studied the issue as a PhD scientist and conclude that the theory of evolution is a religion.
Spencer is a signatory of the Cornwall Alliance which has "An Evangelical Declaration on Global Warming":
"We believe Earth and its ecosystems—created by God’s intelligent design and infinite power and sustained by His faithful providence —are robust, resilient, self-regulating, and self-correcting, admirably suited for human flourishing, and displaying His glory. Earth’s climate system is no exception. Recent global warming is one of many natural cycles of warming and cooling in geologic history."
And recently Spencer said: "I view my job a little like a legislator, supported by the taxpayer, to protect the interests of the taxpayer and to minimize the role of government"
You have to worry that Spencer believes on faith that climate sensitivity is low because he thinks God wouldn't have made an Earth humans could dangerously harm themselves with through fossil fuel emissions, and is setting out to argue this because he sees it his job to prevent any solution which would involve the role of the government.
For all the crying skeptics do about funding of climate scientists, I think the above is a far more disturbing indicator of potential bias.