( CNN ) -- Just 12 years after the arrival of the 6 billionth individual on the planet in 1999 , humanity will greet the 7 billionth arrival this month . The world population continues its rapid ascent , with roughly 75 million more births than deaths each year . The consequences of a world crowded with 7 billion people are enormous . And unless the world population stabilizes during the 21st century , the consequences for humanity could be grim . A rising population puts enormous pressures on a planet already plunging into environmental catastrophe . Providing food , clothing , shelter , and energy for 7 billion people is a task of startling complexity . The world 's agricultural systems are already dangerously overstretched . Rainforests are being cut down to make way for new farms ; groundwater used for irrigation is being depleted ; greenhouse gases emitted from agricultural activities are a major factor in global climate change ; fertilizers are poisoning estuaries ; and countless species are threatened with extinction as we grab their land and water and destroy their habitats . The economic challenges are equally huge . Population is growing most rapidly in the world 's poorest countries -- often the places with the most fragile ecological conditions . Poor people tend to have many more children , for several reasons . Many live on farms , where children can be engaged in farm chores . Poor societies generally suffer from high rates of child mortality , leading parents to have more children as `` insurance '' against the possible deaths of children . Girls rarely make it to high school , and are often married at a very young age , leading to early childbearing . And modern methods of contraception may be unavailable or unaffordable . When poor families have six or eight children , many or most of them are virtually condemned to a lifetime of poverty . Too often , parents lack the wherewithal to provide decent nutrition , health care and education to most of them . Illiteracy and ill health end up being passed from generation to generation . Governments in poor countries are unable to keep up , their budgets overmatched by the need for new schools , roads and other infrastructure . So the arrival of the 7 billionth person is cause for profound global concern . It carries a challenge : What will it take to maintain a planet in which each person has a chance for a full , productive and prosperous life , and in which the planet 's resources are sustained for future generations ? How , in short , can we enjoy `` sustainable development '' on a very crowded planet ? The answer has two parts , and each portends a difficult journey over several decades . The first part requires a change of technologies -- in farming , energy , industry , transport and building -- so that each of us on average is putting less environmental stress on the planet . We will have to make a worldwide transition , for example , from today 's fossil-fuel era , dependent on coal , oil and gas , to an era powered by low-carbon energies such as the sun and wind . That will require an unprecedented degree of global cooperation . The second key to sustainable development is the stabilization of the global population . This is already occurring in high-income and even some middle-income countries , as families choose to have one or two children on average . The reduction of fertility rates should be encouraged in the poorer countries as well . Rapid and wholly voluntary reductions of fertility have been and can be achieved in poor countries . Success at reducing high fertility rates depends on keeping girls in school , ensuring that children survive , and providing access to modern family planning and contraceptives . Two centuries ago , the British thinker Thomas Robert Malthus famously warned that excessive population growth would cut short economic progress . That is a threat still with us today , but it is a warning , not an inevitable outcome . We face an urgent task : to adopt more sustainable technologies and lifestyles , and work harder to achieve a stable population of some 8 billion or so by mid-century , rather than the current path , which could easily carry the world to more than 10 billion people by 2100 . The opinions expressed in this commentary are solely those of Jeffrey Sachs .
Jeffrey Sachs : Earth 's population will hit 7 billion this year ; milestone , huge challenge . He says with earth 's resources already stretched thin , rapid growth is cause for concern . He asks : How do we increase opportunities for all , leave a usable planet for future ? Others : Vital to switch to sustainable agriculture , cut fertility rates .