The largest problem the world has is the sheer mass of the ever-increasing human population. This never seems to be addressed, as a taboo subject. The population growth needs to be stopped, and the actual population needs to be decreased. This could be done by natural attrition, by just limiting child-births.
This would then make the consequences of unlimited growth unnecessary, - war, disease, famine, starvation, and suffering. It is sad that various leaders can make grand sounding speeches that mean nothing. Without government and religious intervention, to change peoples attitudes, and to mandate change- it's easy to predict the outcome of more and more desperate exploitation of dwindling resources, increased consumption and unchecked pollution. Unfortunately a lot of Religious groups believe that it is a person's duty to increase the population, that there is no population problem, and if you have faith, everything will be fine- so there are no consequences to irresponsible action. Roman-Catholics, unfortunately, also don't believe in birth control. It would be nice if the Pope could actually reverse some of this thinking, encourage birth-control and convince people that it is imperative that they be responsible and good stewards of our environment.

While most of the world's man-made climate ills can arguably be tied to population growth, a growth which is exploding phenomenally, population control is not a simple matter. We are biological beings with an virtual imperative to reproduce. Just look at how pervasive an element sex is in all aspects of life from laws, to commerce, personal relationships. I think the important question here is not whether we can control human nature but rather what price do we pay if we try or even succeed.

I think mankind would have a much easier time accepting the pains of disease and war than the restriction of reproduction. Many species, including our own, have survived because the compulsion to reproduce is so strong that we had the numbers to withstand catastrophes.