1. Apparently some ecological problem exists. There are various causes. Deforestation is not the entire problem. Deforestation only represents the equivalent of one part of the problem if we assume there are six equal parts. (However, in your paragraph, we don't know how many other causes there are.) 2. Yes, you can say, "there is that." "there" is often called a "dummy pronoun". It is used to indicate the existence of something. For example, "There is a fly in my soup." "that" is simply the well-known adjective that identifies or singles out something that is known. For example, "Give me that book" (Not just any book, but the particular one I've singled out.) So "there is that political will and urgency" means, "A certain political will and urgency exists". 3. "entirety" means the whole thing; all of something. "I never read excepts from a book. I always read the book in its entirety." "I know something about China, but I don't know the entirety of its history."

A "sixth" is a fraction. Therefore, this sentence means that if "our problem" was divided into six pieces, "deforestation" would be one of those six pieces. "There is that" should be seen more as "There is" "that political will..." because the "that" in the sentence is referring to the "political will and recognition." The subject of this sentence is being emphasized by being put at the beginning. If you rearrange the words into "That political will and recognition is there" it means the same thing. "Entirety" means the state of being entire, complete, or whole. Deforestation is one sixth of the problem, but the whole (entirety) of the problem must be solved.