I don't think democracy is quite as ideal as you think there, kolben.Democracies rely on politicians, whose primary goal is often their career. Whatever course of action that will lead to a government staying in power, will be taken by the government.
This totally disempowers democratic governments from doing things that would be unpopular. This would be fine in an ideal world, as in an ideal world nothing unpopular would need to be done. Ideal the world isn't.
The main problem the world has, as i see it, is the population growth curve. The number of people on earth is rising exponentially, and nothing significant is being done to combat this.
Look at the natural world, rescources for each creature to survive have to come from somewhere.. We have grown sufficiently good at processing the planet to allow for huge rescource usage, but in doing so we destroy many of these rescources. There are widespread environmental issues now, due to our rescourse usage, and this is mainly due to the exponential population growth.
It will be too late, under a world governed by democracies, that enough is done to kerb this growth. The species will be doomed by that time.
What can be done to avoid such a shortfall problem? Why, simple, Kill 2/3 of the population at random, is what i would recommend. It needs done. It won't be done.
We are doomed.