Am I worrying needlessly about the ambiguity in the first title? Overall reactions?
Nope, I am pretty sure anyone's first read would be the wrong one. With a political topic like that, "Climate Fever" is going to read like a belief and not a description of the climate.
But "Fevered Climate" sounds awkward to me. "Fevered Planet" made more sense: a planet can have a fever. A climate can't have a fever; the fever IS the climate. Your climate may vary.
What about "Solving the Climate Crisis"? It catches my attention immediately. Is Beyond Market Tinkering required?
Climate Fever sounds like Jungle Fever, like someone really has a thing for climate.
"Solving the Climate Crisis" has a good flow of sound, as well.
Solving the climate crisis: more than market tinkering
(Reason for subtitle :need something to convey that it is about policy rather than tech and that it is not yet another "put a price on carbon" book)
How about
Cooling a Fevered Planet: Political Solutions for the Climate Crisis.
The Climate Crisis: We're not totally screwed yet.
It is good, but it nothing in that to rule out policy that concentrates putting a price on carbon.
I was very attached to "Cooling a Fevered Planet" too. The problem is that while good look it does not do its share of the work. "Cooling a Fevered Planet" does not tell the reader that the book is about the climate crisis. Could be, but could be about war fever, or overconsumption or hundreds of things. So the subtitle can't start with assuming the reader has learned anything from the title, and has to carry 100%. That leads to a too long subtitle, or a title:subtitle combo that does not convey minimum information. A thought. You can cool a crisis. So what about:
"Cooling the Climate Crisis: More Than Market Tinkering" or
"Cooling the Climate Crisis: Post Carbon-Pricing Politics"
Hmm - "Post Carbon-Pricing Politics" does all the work I need , so I could even get fevered planet back:
"Cooling a Fevered Planet: Post Carbon-Pricing Politics"
or reverse the order for a colon free -
Post Carbon-Pricing Politics to Cool a Fevered Planet