Malthus wrote "Essay on the Principle of Population" in 1798. He predicted that population growth would lead to starvation and that increasing food production would only increase the population growth until it again reaches to the issue of starvation. Poverty is inescapable and related directly to population growth.
In early 2000 a professor of the University of Texas predicted humans had already reached the carrying capacity of the earth and increasing problems related to population and signs of the stress were already developing. He was then condemned as an abortion proponent when all he was saying was something had to be done to slow down population growth without mentioning abortion.
The city of San Antonio is reaching the limits of the gigantic underground Edwards aquifer that supplies the city with water. They are now considering pumping water from lakes to the north.
Despite what we know will eventually happen the population of the world is growing faster with only disaster ahead. Despite this we are advancing medicine to save lives and let people grow older and increasing the demand on the earth for more food and water.
Is uncontrolled population growth a moral issue and if so how can we respond?
In the short term, people electing to have fewer children overall -and campaigns to show that such is necessary and beneficial -would be the best way to address such a problem where it exists -whether locally, or eventually globally.
Doing so is as "green" as anything else people might do for the benefit of all.
From a biblical perspective, it will not be a local issue for long -and things will change before it becomes an extreme global problem.
Unfortunately, the first change is a decimation of population due to war, famine, disease, natural disaster -and even, toward the end, the returning Christ defeating those who attempt to war against him at his return (search: "Then shall the Lord go forth and fight against those nations", "shall destroy those who destroy the Earth" and "these shall make war with the Lamb") -and various "last plagues".
Fortunately, "the slain of the Lord" will all be resurrected, have the opportunity to live forever -and be given a "glorious" spirit "body" with extreme creative power similar to that which allows the Word who became Chrst to "subdue all things into himself".
"Science" is beginning to realize that we can not practically go out into the universe as humans -but such a body will allow for it.
It is written that "the heavens" we're not made "in vain" but "formed to be inhabited."