Population growth

Population growth is the increase in the number of people within a specific group or across the entire planet. Scientists measure this change using a population growth rate. This rate is the change in population over a specific unit of time. It is usually expressed as a percentage of the individuals present at the start of that period. A positive growth rate means the population is increasing. A negative growth rate means the population is decreasing. If the rate is zero, the population size remains the same.

Most populations do not grow forever at the same speed. Instead, they often follow a logistic model of growth. In this model, growth eventually slows down as a population reaches its carrying capacity. Carrying capacity is the maximum number of individuals an environment can support. This limit is usually reached when a population uses up most of its available natural resources. In recent decades, however, the total human population has appeared to follow a more linear trend.

Human population growth has a long and complex history. The global population began rising continuously after the Black Death ended around 1350. Growth became much more rapid during the Industrial Revolution in the Western world. The most significant surge in numbers has occurred since the 1950s. This massive increase was driven by medical advancements and higher agricultural productivity. One major factor was the Haber process. This process was named after the German chemist Fritz Haber. It allowed for much more food production. This single discovery helped the population jump from 1.6 billion in 1900 to 7.7 billion by November 2019.

Researchers have studied why these changes happened. A British health scientist named Thomas McKeown investigated the modern rise of population. He proposed the McKeown thesis to explain growth in the 19th century. He argued that growth was not caused by more births. Instead, he believed it was caused by a decline in mortality, or death rates. Specifically, he noted a drop in childhood and infant mortality. McKeown suggested that rising standards of living and better nutrition were the main causes. He questioned if public health measures like vaccinations were as important as others thought. While his ideas are still debated, they remain very influential in social medicine today.

Today, the scale of human population is immense. In 1800, there were only 1 billion people on Earth. By 2025, that number reached 8.2 billion. The annual growth rate peaked in 1963 at 2.2% per year. Since then, the rate has been declining. In 2017, the growth rate was approximately 1.1%. Currently, the global population grows by about 70 million people every year. This represents an annual growth rate of roughly 0.85%.

Different parts of the world experience growth in very different ways. Many developed nations are seeing a slowdown in growth due to the demographic transition. This is a process where high standards of living lead to much slower population growth. In contrast, less developed regions still see rapid growth. For example, some countries in Sub-Saharan Africa and the Middle East have growth rates above 2%. Some nations are even seeing their populations decline. Japan's population began to decrease in 2005. In Eastern Europe, low fertility rates and emigration have also caused declines.

Looking toward the future, experts have different projections. The United Nations projects that the population will peak in the mid-2080s. They estimate this peak will be around 10.3 billion people. Other groups, like the Institute for Health Metrics and Evaluation, predict an earlier peak of 9.73 billion in 2064. Rapid population growth creates significant global challenges. Increased numbers and consumption can drive environmental concerns like climate change and biodiversity loss. To address this, international policy focuses on the Sustainable Development Goals. These goals aim to improve human well-being while reducing our impact on the natural environment.