Pour le 3 si on doit les relier ensemble je crois que ca donnerais ca :
1- Scientists are still divided on the impact of global warming but they agree it is caused by human activities.
2- Global warming in a proven fact that scientist cannot assess how much it will affect us.
3- world is warming at an unprecedented rate so nobody can predict what will happen precisely.
4- It is comforting to know that people study this problem and the changes taking place that are extremely worring.
Mais je ne suis pas sure