I'd instead say that "I can't say that global warming is a fact. But science never works that way - you can disprove a hypothesis, but never prove it. When a hypothesis is confirmed again and again by alternative hypotheses being disproved, it is considered to be correct for the time being."
Part of the problem is that scientists know how this works, but ordinary people and politicians don't. The scientists don't adapt their language to their audience. Maybe they should instead state flatly that our current course of action will in the best case lead to widespread war and famine, in the worst case to total devastation.
I don't think you can convince the fossil industry to pack up and go home because it would be beneficial to society as a whole. I think fossil fuel burning must be banned or taxed out of existence, and to do that, the majority of the voters must realize that business as usual will probably ruin the future of their children and grandchildren.
That's why carbon should be expensive. A carbon tax, the proceeds of which is evenly distributed to all taxpayers would work, I think.
You have good points-my 0.02:
Scientists are not marketers and asking them to put together a compelling message that changes behavior of people is misguided.
As a matter of fact most scientists are profoundly unscientific when asking how to get the message out. There is more evidence that facts don't influence consumer behavior and policy. Keep the scientists in the lab and get a PR company to create demand for the welfare of our grandchildren with a proper budget, campaign etc.
There is plenty of historic and current evidence that we are not rational species when it comes to crisis. I don't trust a democratic system which allows 5% of the world population to vote on representatives with only a tenuous influence on an industry that sees regulation as an obstacle towards economic goals. How's it working so far?
Carbon tax is the scheme proposed by some agencies and pioneers of global climate actions (eg Hansen, etc). I like it- are there precedents of adoption?
Also you have to wonder when nations and individuals more vulnerable to warming will take unmitigated emissions as an act of war and retaliate against countries, companies and facilities demonstrably hurting their future.
X1188. Sorry if this is terse, sent from my phone.