Assuming this is the book "False Alarm: How Climate Change Panic Costs Us Trillions, Hurts the Poor, and Fails to Fix the Planet" I don't think you can seriously take it as a piece of serious balanced research.
The book titles itself based on what it is, which is the same thing as hundreds of other books peddling cherry picked facts to say that the "establishment" is wrong on climate change. These books take whatever micro-divergence from climate models is currently being observed and trump it up as a refutation of all climate models and of the entire macro-trend.
15 years ago it was the lack of deep ocean warming which has now been observed. I'm sure that in 2021 there are innumerable discrepancies and poorly understood phenomena which could be used for this purpose.
> a refutation of all climate models and of the entire macro-trend
Is this Lomborg you're saying is a denier? What are you basing that on?
I can believe that he is encouraging others who want to do nothing about climate change, but I didn't think he was objectively a denier. People calling him one may be playing into his shtick.
If he's not denying climate change, then it's a lie or willful disregard for the truth to say he is, and encourages the people who think it's a religion and a conspiracy. The morality of slander is not even the point, it's that tactically, you don't want to be seen making unfounded attacks because you're essentially ad-hominem'ing yourself.
I read a book of his a long time ago, and I am not 100% sure he isn't a denier these days, but he wasn't then, even though he definitely was trolling as hard as he could.