The earth’s carrying capacity is something that I have research in detail. Population growth is a serious problem. But, even if the population were to be held at the present value, or lowered, the ability of the earth to sustain the human population is in danger due to the environmental devastation of extraction, production, consumption, contamination, and waste generation.
The earth will only be able to sustain human populations, without crisis, if there the population is held within limits, the lifestyle of humans (particularly those from the developed world) are brought back to sustainable levels, and renewable energy (solar, wind, geothermal, etc) replaces non-sustainable and fossil fuels.
We must also be careful to go about bringing about these changes through democratic with peace, justice, and equity and as priorities. Recall that in Puerto Rico, calls for population control, in the mid 1900’s, were used as justifications of white Americans in implementing racist mass sterilization on unsuspecting women called La Operacion (See: http://www.filmandhistory.org/documentary/women/operacion.php) . Also note that those who promote Nuclear power often fail to acknowledge the devastating impact uranium mining has on indigenous populations where approximately 70% of uranium deposits are found (http://www.wise-uranium.org/uip412.html).