They shouldn’t. They should both be treated as consultant reports only. Both are advocates for their beliefs and should be treated as such, just as an oil company, or UN report.
Why in the world should the UN be given any more credibility than tobacco companies? They’ve proven time and again how self serving and corrupt they are.

It’s the job of the “elected” policy maker to look at all sides and determine the best course of action or inaction for the good of the country, period. Unfortunately, in our system of government, (US) lobbyists and special interests have way too much sway over the results. Add to that equation the role of the media picking a side and proceeding to hammer the populace with it on a near daily basis, and you have the makings of a real mess. Hense we have our No-Energy Energy Policy, and piles of other nonsensical, but real expensive legislation.

The drive to reduce our CO2 emissions is more important from an energy security perspective - we have known for quite a while that China can and will buy oil at any price to drive its development. From a policy perspective, this causes us a big headache.

Which links into the money. Examples where science has influenced policy include smoking and obesity. Government interference in these issues relates to reducing health expenditure.

Your question is a tough one. Of course scientists should be involved in crafting policy decisions. But perhaps they should also be trained in economics, politics and policy making beforehand, instead of just being used by people who are.

The majority of scientists seem to have little clue about international affairs beyond what they read in the newspapers. And vice-versa for the policy makers vis-à-vis science.