A man you don't know, have never met, and have no reason to trust, comes up to you and gives you a delicious juicy apple. He assures you the apple is perfectly fine and healthy for you to eat.

You  want to believe him because you love apples and this one looks perfect. He seems like a genuine guy and you have no real reason not to trust him but you can't make up your mind what to do. Trust and enjoy the apple, or be excessively cautious and go without.

Then another man you don't know, have never met, and have no reason to trust, comes up to you and pleads with you not to eat the apple because he knows it is poisoned and that even though the effects may not be immediate, he knows it will eventually cause major healthy issues and possibly death. 

Two opposing pieces of information from two seemingly equally believable, reliable and convincing sources but without proof either way, the decision is overwhelmingly obvious. You must put aside your love of apples for caution and self preservation. The apple may be good, it may be poisoned but you can't risk it. You don't eat the apple. 

Why then, when some people tell us that climate change is a hoax and we don't need to do anything, and some actual scientists with proof say climate change is real, dangerous and the biggest threat to all life on a global scale, does our logic for caution and self preservation vanish? 

We are ignoring the man with proof of the deadly apple, and we just keep on taking big bites.