The equation is not rocket science. Two billion people, all else being equal, put more greenhouse gases into the atmosphere than one billion people. Two billion rich people disrupt the climate more than two billion poor people. Three hundred million Americans consume more petroleum than 1.3 billion Chinese. And driving an SUV is using a far more environmentally malign transportation technology than riding mass transit.
Areas of high population such as the Americas but also those that have wealthier residents are major contributors to the environmental impact as they consume the most.