I agree with DuncanONeil...this will NEVER happen.
Let's say for instance that the extended consultation with multiple scientific sources has occurred. No matter what the heads of governments are told is the best course of action, it is virtually impossible that all of them will agree to the same plan of action. A smaller, third-world type nation is going to feel like its "big brothers" are taking advantage. Some countries will feel like the world powers (US, UK, China, Japan, etc) created the mess so why should they have to do ANYTHING to help clean it up? Heck, even the world powers won't agree on things.