the global human population", even mass mortality events and draconian one-child policies implemented on a global scale would still likely result in a population of 5 to 10 billion by 2100. Therefore, while reduced fertility rates are positive for society and the environment, the short term focus should be on mitigating the human impact on the environment through technological and social innovations, along with reducing overconsumption, with population planning being a long-term goal. A letter in response, published in the same journal, argued that a reduction in population by 1 billion people in 2100 could help reduce the risk of catastrophic climate disruption. A 2021 article published in Sustainability Science said that sensible population policies could advance social justice (such as by abolishing child marriage, expanding family planning services and reforms that improve education for women and girls) and avoid the abusive and coercive population control schemes of the past while at the same time mitigating the human impact on the climate, biodiversity and ecosystems by slowing fertility rates. Paige Whaley Eager argues that the shift in perception that occurred in the 1960s must be understood in the context of the demographic changes that took place at the time. It was only in the first decade of the 19th century that the world's population reached one billion. The second billion was added in the 1930s, and the next billion in the 1960s. 90 percent of this net increase occurred in developing countries. Eager also argues that, at the time, the United States recognised that these demographic changes could significantly affect global geopolitics. Large increases occurred in China, Mexico and Nigeria, and demographers warned of a "population explosion", particularly in developing countries from the mid-1950s onwards. In the 1980s, tension grew between population planning advocates and women's health activists who advanced women's reproductive rights as part of a human rights-based approach. Growing opposition to the narrow population planning focus led to a significant change in population planning policies in the early 1990s. Population planning and economics Opinions vary among economists about the effects of population change on a nation's economic health. US scientific research in 2009 concluded that the raising of a child cost about $16,000 yearly ($291,570 total for raising the child to its 18th birthday). In the US, the multiplication of this number with the yearly population growth will yield the overall cost of the population growth. Costs for