It is overpopulated past the point where the human made infrastructure can reasonably support it and the Earth itself can compensate for the damage we are doing. We have land available for growing food, but we can't transport that food to areas where little is available. The issue of climate change or global warming isn't strictly a matter of polluting the environment. Too many people need too many factories to make too many things to support the lifestyle they believe is their right to have.
When forests are destroyed for people to build When water is scarce because people have polluted it When the ocean is dying because of oil spills When the arctic and Antarctic are melting because of the green house affect... The earth is overpopulated, yes.