The image depicts a possible trajectory for our human species: after an exuberant eruption of people and their playthings, an understanding of the finitude of the Earth system emerges, and we rein in our procreation and our consumption so as to live sustainably within that system. Instead of hitting the wall when our combined expansion curves go vertical, by reducing our demands on the planet we enable our species' existence to continue, as a more modest but still significant part of the biosphere, on into the long-term future.
The left-hand portion of the lower figure traces the human population growth curve from the year 1 A.D. to the present. For all of our evolutionary history up until around 1750 A.D., we numbered a billion or less worldwide. With the industrial revolution, improvements in public health, and increasingly intensive agriculture, we have multiplied ourselves more than seven times over, drawing down fossil solar energy deposits, co-opting almost half of the yearly photosynthetic production of green plants around the globe, and pushing more and more of the Earth's other species right out of existence in the process. The right-hand portion is the mirror image of our species' youthful yang explosion, reflecting the activity of an older and wiser yin approach, operating in reverse. After a global awakening, we consciously, voluntarily, and deliberately limit the sizes of our families and our collective demand on the renewable fountain of energy that supports all Life on Earth. A portrait of our planet as seen from space hangs in the "sky" to remind us, not only that the Earth is a finite sphere, but that we humans are a single species, and that we no longer need to war against ourselves as we become responsible citizens of the planet.