The grim news is that it would take a substantial reduction in carbon dioxide emissions to limit concentrations to their present levels. As humans become ever more numerous and consumptive, our emissions and pollution begin to rival natural processes of nature's cycles. At first this occurs locally, then at regional scales, and finally globally. Global atmospheric pollution is the first of earth's reservoirs to be affected because it is the smallest. It is also true for sulfur dioxide and nitrogen oxides.
Human effects are pervasive.
In 1750, when the global population was one billion, people had an average of 29 acres of habitable land per person, but today the number is about five acres. And in these five acres per person, we must feed ourselves, supply shelter and energy, and allow for the cohabitation of four million or more species of plants and animals. The world is still a big place and much accommodation is possible, but only with education and good government can we make progress towards providing for humans while not despoiling the environment.