Could the soverign governments of the world enact policies and cooperate in order to reduce air and sea and land pollution?

The UN conference in Rio de Janero in 1992 was an effort to do just that and they came up with Agenda 21. The assumption behind its formation was that without these measures the survival of humanity was at stake. The assumption is correct that if mankind doesn't change his ways he will kill himself. The MEANS of changing the ways of mankind in a positive way is up for debate, however.

There are two dominant philosophies of how humans should interact and govern each other for the betterment of mankind. Both are rooted in a belief about reality. Secular humanism, one of them, believes that man is supreme in the universe, or at least here on earth, and must take matters into his own hands through policies grounded in the ethic of being for the greater good. Christian theism, the other major global philosophy on the nature of reality, takes the position that the individual rights of each human being takes precedence over the good of society.

The tension between these two ideas is extreme. Theists believe governments, like the entities that met in Rio in 1992, have only one responsibility and that is to protect the rights of human beings that were endowed to them by their creator. (The American constitution and declaration of independence is the premier statement of that belief.) Humanists believe that governments determine, issue and rescind human rights based on the determination of what is best for the society as a whole.

It's a self evident truth that the vast majority of the global governments of sovereign nations, and the various organizations of these nations like the UN, are practicing secular humanism. The biggest difference between the two philosophies in real time is that ethically secular humanism has nothing within it that inherently condemns the use of any means necessary to accomplish the end result.