“The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available.” 
In population ecology, carrying capacity corresponds to the population equilibrium, when the number of deaths in a population equals the number of births (as well as immigration and emigration). The notion of carrying capacity has been applied in various contexts, and since the 1950s, has been closely associated with the idea of human population limits and sustainability. 
The human population, now nearing 8 billion, cannot continue to grow indefinitely. There are ecological limits to the life-sustaining resources our planet can provide. It is very difficult for ecologists to calculate human carrying capacity, however. Humans are a complex species, and do not reproduce, consume resources, and interact with our living environment uniformly. Estimates of carrying capacity require predictions about future trends in demography, resource availability, technological advances and economic development. 
Today, the impact of the human population on the planet, or our global footprint, is in overshoot. It would take 1.75 Earths to sustain our current population. If current trends continue, we will require the resources of 3 Earths by the year 2050.