We represent several generations of biology educators – with teaching experiences beginning in the 1940s and continuing to the present, from elementary school to graduate-level programs. We find the vast array of subjects that biology teachers can now cover both thrilling and mind-boggling. Depending on the grade level, units exist that focus on neurobiology, forensics, DNA analysis, biotechnology, marine biology, and a host of other topics.

Although science teachers cover a potpourri of advanced topics, we must ask ourselves – no matter our biology-teaching responsibilities – how well we are teaching carrying capacity, one of the most fundamental biological concepts for our society, knowledge of which becomes more important every day. As biology teachers, most of you know that carrying capacity is defined as the maximum population an environment can sustain, given the amounts of food, habitat, and other resources available. Every environment – from your goldfish bowl to the local forest to planet Earth – can only sustain a set number (weight) of a particular species, based on available resources and space. Currently, most science classes teach that humans should conserve resources and live sustainably. However, do we adequately emphasize why this is vital? Do our students understand that a particular area – or our planet – only has so much to provide a given species living there?

Why should carrying capacity receive increased emphasis in our biology classes? Perhaps the most compelling reason is that if we don't emphasize its importance, grave consequences for humankind await. Inability to live within the limits imposed by carrying capacity has repeatedly contributed to the demise of societies – including, for a very few examples, ancient cultures such as the Mayan and Mediterranean Bronze Age civilizations, many Chinese dynasties, and the Greenland Norse, as well as modern societies such as Rwanda, the Empire of Japan, U.S. Dust Bowl communities, Canada's cod-fishing communities, and nations in the Horn of Africa. These societies collapsed because their human populations and resource use increased to unsustainable levels, or to levels barely sustainable with existing resources, and then additional stress – through a change in climate or other factors – was placed on the system, reducing the carrying capacity of the area. Unavailability of sufficient resources to support these populations contributed to tragic consequences such as abject poverty, massive societal restructuring, human migrations, and warfare.

With the human population on Earth exceeding 7.2 billion, many scientists argue that our population size and our resource use are approaching the carrying capacity of our planet. Human-caused climate change exceeds anything that could be expected under natural climate cycles. Solutions to the problem include family planning, resource-use management, or improving technology to increase carrying capacity. However, if solutions are to be found and employed, students must understand the concept of carrying capacity and the consequences of ignoring it. Here biology teachers can make a major difference.

You might say, “I already teach about carrying capacity!” That may be, yet somehow, its importance and relevance are still not widely understood or accepted. In the latest four Gallup polls, only 1–3% of Americans consider environmental problems the most pressing issue our country faces. Approximately 40% of Americans think that climate change is a natural cycle, contrasted with 97% of climate studies which state that humans are causing it. Natural resource scientists hear government officials, newscasters, and members of the general public offer as ecological “facts” notions that are breathtakingly wrong. It seems clear that scientific information has outpaced the efforts of science educators and communicators to help society move towards understanding carrying capacity and taking action to live within our means.

Fortunately, the prognosis is not all bad. Humans, unlike wildlife, can consciously reduce our effects – if we understand carrying capacity, and incorporate its importance into our value systems. Biology educators are in a powerful position to effect change by reemphasizing the concept of carrying capacity at every educational level, in all nations, as part of core curricula. Groups such as POGIL (Process Oriented Guided Inquiry Learning; https://pogil.org), Population Education (https://www.populationeducation.org/content/what-carrying-capacity), and Lesson Planet (http://www.lessonplanet.com/lesson-plans/carrying-capacity) provide exciting suggestions for teaching the subject in various grades. Educators could refamiliarize themselves with carrying capacity by studying the excellent overviews offered by writers such as Jared Diamond, Gretchen Daily, and Paul R. and Anne Ehrlich.

If our societies are to endure, the concept of carrying capacity and living sustainably should be as familiar to every student as 2 + 2 = 4. Almost 60 years ago, one of us, John Bonar, then a young biology teacher, watched Soviet Sputnik I, the first satellite to orbit Earth, pass overhead. Americans feared the Soviet triumph, and a revolution in science teaching occurred as our country shifted gears to emphasize science education in order to compete with the Soviet Union in the “space race.” With changing climate and human population growth reaching critical levels, another “Sputnik moment” may be necessary to help us avoid exceeding our planet's carrying capacity. This problem is arguably more critical than the space race, and it is within humankind's ability to control. In this endeavor, educators can play an indispensable role. To those of you who are already emphasizing carrying capacity in your classrooms, congratulations. To those who are not, please consider taking up the challenge to teach the concept and its implications wherever possible. Our future may depend on the success of this mission.