“In the last 200 years the population of our planet has grown exponentially, at a rate of 1.9 percent per year. If it continues at this rate, with the population doubling every 40 years, by 2600 we will all be standing literally shoulder to shoulder” Stephen Hawking

The world population is almost 7.6 billion and growing. It is projected to reach 8 billion by 2025, 9 billion by 2040, and 11 billion by 2100. The rapid growth is raising serious questions for the planet’s carrying capacity.

The impact of human population dynamics on the environment takes two major forms: first, the consumption of natural resources such as land, food, water, air, fossil fuels and minerals; second, the production of waste as a result on consumption e.g. air and water pollutants, toxic materials and greenhouse gases. Overpopulation results in overconsumption of resources and consequent depletion of natural resources. The overpopulation is putting an incredible strain on our environment and resulting in shortage of food, reduced access to public services, overcrowding and high unemployment.

The expanding world population demands a wider agricultural base (more agricultural land), land for living on and other life supporting activities, leading to deforestation. Deforestation is to Earth what collapsing of the lungs is to a human, it leads to a reduced ability to fix carbon dioxide and hence intensifies the greenhouse effect. Deforestation is also strongly associated with loss of habitat and species extinction. Agriculture is the major motive for large-scale deforestation.

Intensive agricultural practices, characterised by excessive use of pesticides and chemical fertilisers are other sources of environmental degradation. The agricultural runoff of excess fertilisers is one of the key causes of eutrophication, depleting oxygen contents of water bodies and consequently threatening marine life. Worldwide ‘dead zones’ caused by eutrophication now cover an area the size of UK.

Only 2.5 percent of global water resources are fresh waters. Only a small fraction of that is available unpolluted. Global aquifers are being depleted 3.5 times faster than the natural recharge rate by rainfall. Hundreds of millions will suffer as some of these run dry. The overpopulation has water stressed many communities and countries. The situation is projected to aggravate substantially by 2025.

The depletion of natural resources manifests itself in a number of ways. The topsoil is being lost at 10-40 times faster than it is formed; the oceans are overfished so that a primary protein source for over 2 billion people is in jeopardy; the ozone layer has depleted and many species are facing extinction.

With the rapid growth in human population, the number of malnourished in the world is also on rise (it has risen from 20 percent in 1950 to 66 percent in 2010). The stress on food production is increasing because of shortages of natural resources like cropland and fresh water. Another key ingredient that determines the yield of crops is fertiliser. The production of fertilisers in turn consumes natural resources like minerals (phosphates, potassium, and micronutrients) and fossil fuel, both for their mining and processing.

Global aquifers are being depleted 3.5 times faster than the natural recharge by rainfall. Hundreds of millions will suffer as they run dry.

The high standards of living in modern world are dependent on non-renewable resources such as fossil fuels (like oil, gas, and coal,), metals and alloys (like steels, aluminum and copper). Almost two-thirds (63.3 percent) of global electricity and nearly 80 percent of transportation energy comes from fossil fuels. The growth in and human population and increase in the use of fossil fuels have grown hand in hand with increase in carbon dioxide emissions. A recent study shows that at a European standard of living the Earth can sustainably support a maximum of 2 to 3 billion people.

Our planet is a closed system. All of its resources - air, water, land, food, fossil fuels and minerals - are limited and cannot be added on. Today humanity uses the equivalent of 1.5 planets to provide the resources we use and absorb our waste. This means it now takes the Earth a year and six months to regenerate what we use in a year.

One of the largest environmental effects of human population growth is the problem of global warming. Since the beginning of the Industrial Revolution, the concentrations of carbon dioxide and methane in atmosphere have increased nearly 40 percent and 150 percent, respectively. The planet Earth in its long history has experienced climate change due to various reasons like subtle shifts in its orbit, volcanic eruptions and variations in Sun’s energy. But the current enhanced warming at an ever increasing rate during the past 250 years is related to the greenhouse gases emitted due to human activity.

The amount of carbon dioxide emissions resulting from burning of fossil fuels is 26 billion tonnes per annum, that is orders of magnitude larger than 130-230 million tonnes of carbon dioxide emissions per year from active volcanoes. In fact, the human influence on climate has eclipsed the magnitude of natural temperature changes over the past 125 years. It is predicted that with the projected increasing consumption of fossil fuel, greenhouse gas concentrations will continue to rise. The average global surface temperatures could rise between 2 and 6°C by the end of the 21st Century. The global warming induces changes in rainfall patterns, intensifies coastal erosion, lengthens the growing season in some regions, melts glaciers and alters the ranges of some infectious diseases.

The expansion of human population and pursuit of better lifestyle will always escalate the overconsumption of fossil fuels that consequently deplete energy reserves and increases emissions of greenhouse gasses. The volume of emissions depends on human population, so that one way to reduce emissions is to cut population growth. Besides acclimatisation to climate disruption will be easier with a smaller global population. The impact of 7+ billion humans on the Earth’s environment is equivalent to the impact of greatest forces of nature. Considering environmental factors, the Earth has moved well outside the realm of natural variability.

The Earth can be considered as a collection of four interconnected and interacting sub-systems of environment, population, industry and government. The interacting nature of this system makes it difficult to manage crisis in any subsystem in isolation.

The relationship between overpopulation and environmental impacts is complex. It requires a systems thinking approach. Human actions on an overpopulated Earth may trigger cascading effects resulting in abrupt changes. This may irreversibly transform the Earth into a planet that is far less hospitable to humans.

How many billion humans can the Earth support? In his book Edward Glaeser professor at Harvard University, describes how 10 billion people will fit within the state of Texas if the entire state was covered in townhomes, the quality of the life is however not promised.

Technology may ameliorate the effects of overpopulation, but it is also possible that it will exacerbate the effects. In the Earth system, the environment is non-sentient, but population and government are sentient parts of the system - the burden of responsibility is therefore on humans.

The author teaches at   SZABIST, Islamabad.