To answer this question correctly � you will need to ask all scientists what they think is causing the rise in mean global temperatures. Having collated the answers, if over 50% respond with the same answer � then that is the correct answer; otherwise the answer to the question is that there is no consensus among scientists, whereby over 50% are in agreement on the reason.
Not wanting to prejudge the result of your task � I would be surprised if most scientists thought that the rise in mean global temperatures is caused by a notion widely held by politicians.
Best get on with the task � especially if your homework is due in by next Tuesday.