I really loved this book. (sorry ahead for any following english mistakes. English is only may second language)
Starting with the Characters. I kind of just fell in love with Theo and Hester. With Hester more than with Theo, because she goes through a way bigger devolopment. The little romantic subplot really appealed to me too. In general I really liked the Charakters. One thing I want to point out too, is how divers the cast was and how normal it was treated. There was a non binary Charktere, there was a lesbian couple. That was in my opinion very well done.
I struggelt quite a bit with the writing style of the book. Not that it was bad or anything, but english is only my second language and I found it quite hard to read with my 6 years of school english. I don't know if it was written in a very complicated english or in a very informal english, but it was quite hard for me. But I would not put that on the book, because it is not marketed in any way for people who do not have the motherlanguage english. 
The consept is what drew me at the book in first place (right after the cover, which I found to be gorgeous). I think the topic of climate change is really well done. It portrayed it in my oppinion really realistic, bit still kept a hopefull undertone, which is very impotant when dealing with such a sensitive topic. The Idea of the green fingers only helped it. The consept of them seemed real and I really liked, that they were not being idealist. The book also showed the many problems with such powers appearing and our world reaction seemed really realistic. Just very very well done.
Then the plot it self. Oh what a suprise, I think that was really well done. Most of the book is first just the teenagers and the world coping with these appearing powers. Companies trying to make money of it and the goverment being totally overstrained by it. And we also get a lot learning about climate change it self and a lot charaktere development. Only by the end a really big and exciting plot appeared. But the beginning of learning and evrything was so well done, that also while reading that I barely could put the book aside.
I generally just really loved the book. Although I struggelt a lot with the english, reading it was worth it. The consept is realy great and important and most of all really well down. The Charakters felt really divers to me and I generally just loved them. I loved evrything about that book and I think evrybody should read it. It is just really important and well down. Read it.