Hello, everyone!

The European Union wants talks on a new global agreement covering all nations to start as soon as possible.
It is backed by most of the world's poorest countries and small island states vulnerable to rising sea levels.
But even if resistance from the US and others can be overcome, it is hard to envisage anything being agreed that can start to reduce global greenhouse gas emissions before 2020.
And that is the timeframe science suggests is necessary if the most dangerous climate impacts are to be avoided.

Can anyone give me a detailed explanation of the last sentence about its grammatical structure? I can grasp the general meaning. But i need to know which part is the subject, which part is the predicate and which parts modify others.

Thank you in advance.