The scientific community disagrees about
a. the rate of global climate change
b. the occurrence of global warming
c. the need for action
d. all of the above

Scientists don't disagree over the occurrence of global warning: there is a significant amount of evidence for global warning, and it is considered to be established.- we can reject answer b) and d) together with it

Also it is established that humanity must do something to combat climate change. - so we also reject answer c)

we are now left with answer a) - they disagree in the rate of global climate change. This is however not strictly true - there might be some disagreement about the exact rate, the disagreement is not big. It's the best answer, but it's also not very fortunate.