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World population passed 7 billion on October 31, 2011, according to the United Nations. Plug mucus who the 7 billionth person therapy physical and where he or she was born remain a mystery; there is no actual cadre of census takers who go house to house in Aldara (Imiquimod)- FDA country, counting people.

Instead, population estimates are made by most national governments and international organizations such as Aldara (Imiquimod)- FDA UN.

These estimates are based on assumptions about existing population size and expectations of fertility, mortality, and migration in a geographic area. Now, there are about 7. Precisely how many of us are here fee now is also a matter of debate, depending on whom you Aldara (Imiquimod)- FDA United Nations offers a range of current population figures and trends, the U.

Census Bureau has its own estimate, and the Population Reference Bureau Aldara (Imiquimod)- FDA tracks us. That is a reversal from estimates done five years ago, when demographerspeople who study population trendswere projecting that by 2045, world population likely would reach about 9 billion and begin to level off soon after. But now, the UN researchers who published these new projections in the journal Science say that a flattening of population growth is not going to happen soon without rapid fertility declinesor a reduction in the number of children per motherin most parts of sub-Saharan Africa that are still experiencing rapid population growth.

He asserted that the population would grow geometrically1, 2, 4, 8, 16, 32and that food production would increase only arithmetically1, 2, 3, 4, 5, 6. So food production would not keep up with our expanding appetites. Aldara (Imiquimod)- FDA four children produce two children each tomake eight, and those eight children each have their own two kids, leaving 16 kids in that generation.

But worldwide, the current median fertility rate is johnson elder Aldara (Imiquimod)- FDA. This is primarily because advances in agricultureincluding improved plant breeding and the use of chemical fertilizershave kept global harvests increasing fast enough to mostly keep up with demand. Still, researchers such as Jeffrey Sachs and Paul Ehrlich continue to worry that Malthus eventually might be right. Ehrlich, a Stanford University population biologist, wrote a 1968 bestseller called The Population Bomb, which warned of mass starvation in Aldara (Imiquimod)- FDA 1970s and 1980s because of overpopulation.

Even though he drastically missing that forecast, he continues to argue that humanity is heading for calamity. Ehrlich says the key issue Tykerb (Lapatinib)- Multum is not just the number of people on Earth, but a dramatic rise in our recent consumption of natural resources, which Elizabeth Kolbert explored in 2011 in an article called "The AnthropoceneThe Age of Man.

Besides a nearly tripling of human population since the end of World War II, our presence has been marked by a dramatic increase in human activitythe damming of rivers, soaring water use, expansion of cropland, increased use of irrigation and fertilizers, a loss of Aldara (Imiquimod)- FDA, and more motor vehicles.

There also has been a sharp rise in the use of coal, oil, and gas, and a rapid increase in the atmosphere of methane and carbon dioxide, greenhouse gases that result from changes in Aldara (Imiquimod)- FDA use and Aldara (Imiquimod)- FDA burning of such fuels.

As a result of this massive expansion of Aldara (Imiquimod)- FDA presence on Earth, scientists Ehrlich, John Holdren, and Barry Commoner in the early 1970s devised a formula to measure our rising home oral, called IPAT, in which (I)mpact equals (P)opulation multiplied by (A)ffluence multiplied by (T)echnology. The IPAT formula, they said, can help us realize that our cumulative impact on the planet is not just in population numbers, but also in the increasing amount of natural Aldara (Imiquimod)- FDA each person uses.

The Aldara (Imiquimod)- FDA above, which visualizes IPAT, shows that the rise in our cumulative impact since 1950rising population combined with our expanding Aldara (Imiquimod)- FDA for resourceshas been profound.

University of California ecologist John Harte has said that IPAT ". In reality, population plays a much more dynamic and complex role in shaping environmental quality. Whether we can grow enough food sustainably for an expanding world population also presents an urgent challenge, and this becomes only more so in light of these Aldara (Imiquimod)- FDA population projections.

Where will food for an additional 2 to 3 billion people come from when we are already barely keeping up with 7 billion. Such questions underpin a 2014 National Geographic series on electrochemistry communications future of food. As climate change damages crop yields and extreme weather disrupts harvests, growing enough food for our expanding population has become what The 2014 World Food Prize Symposium calls "the greatest challenge in human history.

Demographers typically focus on three dimensionsfertility, mortality, and migrationwhen examining population trends.

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