What if it's not lack of will but game theory? Maybe it's actually impossible for a large complex system to act against these trends because there exists no stable game strategy for the kind of large-scale cooperation that is necessary?
* Polio eradication
* The Montreal Protocol on Substances that Deplete the Ozone Layer/Vienna Convention for the Protection of the Ozone Layer
Both are examples of multi-state cooperation that dealt with serious world-spanning issues, the Polio eradication has had the most immediate impact, but Ozone Layer depletion has been checked and the numbers will trend down to 1980s levels over the next 20 years.
There are still polio cases today but pretty much only in areas ruled by death cults who don't care whether their people live or die. So game theory isn't a factor there.