World Population Hits 7 Billion/David Baillo, Scientific American

The good news - the number of children each woman gives birth to during her lifetime has halved since 1950. The bad news, this rate has started to increase in various parts of the world

A very special baby girl was born yesterday in the Philippines. The UN demographers determined that she is the seven billionth citizen of the world. Instead, a baby could have been born to a starving mother in the expanding deserts of Somalia, a war-torn and famine-stricken country. Most likely, she would be born in India, where the rate of births per minute is the highest in the world. And maybe, with a little luck, she would have been born in the USA, as part of a minority that determines, for better or for worse, the fate of the planet that economizes humanity.

And in any case, the birth of the seven billionth citizen raises a question: how many humans are too many? Can the earth support seven billion people over time? Or maybe nine billion or ten billion? Demographer Joel Cohen from the Earth Institute at Columbia University, estimates that "the addition of 4 billion people that occurred in the last fifty years is an unprecedented and extraordinary event that will probably not be repeated in human history"
At the beginning of the 20th century there were only about a billion people on earth. About ten thousand years ago there were only a few hundred thousand, and about 70 thousand years ago there may not have been more than 15 thousand of us.

The birth rate and the increase in life expectancy cause the absolute number of people to continue to rise even though the number of children per woman has halved since 1950. In fact, the population growth rate reached a peak of 2.1% between 1965 and 1970, says Cohen. "We have now dropped to a growth rate of 1.1% per year" he adds, although this means that every minute 150 babies are born in the world.

Consumers

The richest half a billion people in the world produce half of the emissions of carbon dioxide, the main greenhouse gas that causes climate change, while the three billion poor emit only 7%. The average American, one of 312.5 million Americans, uses 88 kg of materials every day: food, water, plastic, metals and other resources. Americans consume 25% of the world's energy output even though they represent only 5% of the total population, and the group of industrialized countries wastes 222 million tons of food every year, according to the United Nations Food and Agriculture Agency.

"While the world's population has doubled, the economy has grown 15-fold, the number of cars has increased 16-fold, and the use of fertilizers has increased 6-fold," says geographer Ruth DeVries of Columbia University. "And there is no sign of a slowdown in consumption on the horizon," especially when everyone wants to imitate everyone else, she adds.

All this consumption requires a lot of natural resources, from large copper mines that scar the landscape to more and more land for growing food. More acres were devoted to growing food between 1950 and 1980 than from 1700 to 1850, and land restrictions are only one of nine deviations from the "sector limits" that scientists have identified, which should concern us: climate change, loss of biodiversity, disruption of nutrient cycles (nitrogen and phosphorus ), increase in ocean acidity, consumption of drinking water and more. "Slowing population growth does not solve all the problems, but it makes it easier for us by slowing the increase in demand," says Cohen.

In the end, the factor that will limit population growth will be what the late economist Julian Simon called "the primary resource": energy. Simply put, will there be enough energy that can be used to provide a good quality of life for those billions of people who will populate the planet today? And we are already encountering these limitations, as can be seen in the rising prices of all products, from food to fuel, in the last decade. "Energy consumption per person in the state of New Jersey has reached the rate of the energy production capacity through photosynthesis in the entire territory of the state even if it were returned to its initial state." says physicist Klaus Leckner, director of the Lenfest Center for Sustainable Energy at Columbia University's Earth Institute. To put it simply, without fossil fuels, the people of New Jersey could not exist on the output of this state alone. This problem may spread as we progress in the 21st century due to population growth.

Energy is the key to the modern economy, but it is possible that taking part in the modern economy is the key to limiting population growth. "If girls and women are given the opportunity to generate income and work, you will see a rapid drop in productivity," says de Vries. Also, the increase in accessibility opportunities has led to a decrease in productivity in many countries around the world, as noted by journalist Fred Pierce in his book "The Coming Population Crash" (Bacon Press, 2010): the population bomb is defused. Women neutralize it, because they want to."

However, it is not just about economic opportunities. Education also acts as a key to lowering the future birth rate. "Almost universally, a more educated woman gives birth to fewer children," demographers wrote in an article published July 29 in the journal Science. According to Cohen, the price of education for every young person living in the world today is about 70 billion dollars.

But the birth rate is not falling everywhere. The birth rate in Indonesia stopped falling and started climbing again. Several countries in sub-Saharan Africa, including Niger, which has a birth record of more than seven children per woman, maintain an average rate of more than four children per woman. Even in the US it seems that fertility has increased and now stands at more than two children per woman in recent years.
The most influential way that an American citizen can take to contribute to solving environmental problems in the world, such as climate change, is to have fewer children.

Under current conditions, each American child born will add about 10,000 tons of carbon dioxide to the atmosphere during their lifetime. For comparison, this is 5 times more than his counterpart in China and 160 times more than a Bangladeshi child. According to researchers at Oregon State University, having one less child in an American family will have 20 times the effect of driving a hybrid car like a Toyota Prius, using energy-saving devices and all other lifestyle savings combined.

The demographic dividend

At least in the coming decades, there will be more people of working age in the world than people who depend on them (children and the elderly) - a demographic dividend of the kind that allowed great economic growth in the past. The great question of the 21st century, as Cohen puts it, is "Is economic development the best contraceptive, or is voluntary contraception the best economic development?"

As for the question of how many people the earth can support, the first to calculate it was the Dutch microbiologist Anton van Leeuwenhoek, who already arrived in 1679 at an estimate of about 13.4 billion people, relying on the population density in his country and the relative size of the rest of the world's countries. Later assessments were no more scientific. They ranged from a billion people to a trillion. "These are political numbers designed to convince people either that there are already too many people or that there is no problem with continuing rapid growth," Cohen wrote in his book "How many people can the world support?" (WW Norton, 1996)

Today the world's population produces enough food to feed all the people alive today and even more. Agricultural farms all over the world produce enough calories to provide a population of 11 billion people with 2,000 calories per day. This happened thanks to man's ingenuity - for example, the modern cultivation of staple grains, such as wheat, in record yields, an event known as the Green Revolution, which has so far overcome environmental limitations.
And yet there are still more than a billion hungry people on Earth today. "The number of people living on less than $2 a day doubled in the 20th century," says Cohen. "Hunger is a choice".

Over seven billion

Adnan Mavic was born on October 12, 1999 in Sarajevo and was declared the 6 billionth citizen on the planet, one of 80 million children born that year. 12 years later, the 7 billionth baby is still one of 78 million children born this year. At the current rate it will take 14 years to reach the 8 billion person and it may take longer to reach the 9 billion person.

However, we have not yet passed the peak, which may reach 10.1 billion people, according to UN demographers. After all, in the 90s, the organization's demographers predicted that the peak would be 7.8 billion people, a number that we would surpass long before the target year of 2030. "The difference of one child per woman throughout her life from now to the year 2050 means a difference of 2.5 billion people worldwide." Cohen said.

As it stands today, the human population will peak and then decline. The world of the 21st century will be an aging world, as seen today in Japan and certain European countries - but there is still a good chance of continued growth in the number of people. The UN recently predicted that we would stabilize at 9 billion people, but now they have corrected themselves and are talking about 10.1 billion in 2100, and it may continue to climb due to the fact that the birth rate has not decreased to the extent and at the rate previously predicted. If the choices we make are slightly different, the numbers will reach 16 billion by the end of the century, a number that may be higher than the Earth can sustain at the current level of life.

"This is both one of the most intimate problems - what people do in bed - and one of the biggest public problems," says Cohen. "What people do in their bed affects many people who are not in their bed."