This column is a reaction to an article in Scientific American Earth 3.0, a quarterly magazine devoted to the environment and humanity's future prospects.

"Population and Sustainability" by Robert Engelman considers our world in 2050 with an estimated 9 billion humans (compared to 6.8 billion currently). The worst problems facing humans four decades from now will be inadequate food for billions and even more people with water unfit for human sustenance.

Currently 900 million humans are malnourished and over a billion have their water infested with disease carrying bacteria. These numbers are sure to grow with 2 more billion people on Earth in the lifetime of some readers of this column. It is useful to consider the history of human numbers.

In the first millenium (1 AD or CE to 1000 CE), the global human population scarcely changed, being about 300 million. This is approximately our United State's current population.

By the year 1500, the world's population grew to 500 million. It took a little more than 300 years to reach 1 billion people, about the time that our nation's area doubled with the Louisiana Purchase. In 1927, humans reached 2 billion people. The third billion was achieved in 1960, only 33 years later.

We reached 4 billion in 1987, a mere 17 year interval. In only a dozen years, humanity surged to 6 billion people. In the past 10 years, we have added 800 million people to Spaceship Earth, a growth of 80 million a year; this yearly growth is a little less than the population of either Egypt or Germany. So it is likely that in 3 years, humans will reach the 7 billion mark.

To have such gains in population, the number of births must exceed the number of deaths each year. For example in the United States for 2007, there were 4.3 million births versus 2.4 million deaths for a net gain in our population of 1.9 million people.

Around the world, there are typically twice as many births as deaths. So to have 80 million additional humans each year, there would be about 160 million births versus 80 million deaths.

So there would be about 5 births and 2.5 deaths every second around the world. If you take 2 minutes to read this column, during that time there would be 300 births and 150 deaths.

Why is this increase in population troubling? Isn't the world big enough for a lot more people?

When we look around our Tri-State area, human settlements occupy about 10 percent of the land, the rest being farms or forests. But this is a rural area, while half of the world's population now live in cities or heavily populated urban areas.

For each human, there are 0.6 acres of arable land globally, only half as much land per person as in 1961. There has been a worldwide migration of people from rural areas to urban areas because of jobs and higher income than staying in the country.

In many parts of the world, water quality is bad. As I mentioned in a previous column, our Mexican neighbors have unhealthy public water so most Mexicans drink bottled beverages.

But there are serious problems with water supply in many countries in the Middle East (Saudi Arabia, Iran and Yemen among them); here the underground aquifers are being drawn down rapidly and major rivers are suffering because of melting of glaciers (needed for year long flow).

In some large Asian cities (Beijing among them), wells go down 3,000 meters (0.6 of a mile) to get water for their population's water. These wells use much energy to pump the water to the surface. Once the aquifers are exhausted and the glaciers gone, water will be much scarcer.

The worst thing about global population patterns is that the population growth is highest in countries where most of the people currently have low living standards. Pakistan in 2007 had 169 million people, which are projected to grow to 295 million people by 2050.

Nigeria's population may nearly double (to 282 million) in the same time span. My feeling is that these developing countries in Africa and Asia surging in population will suffer catastrophic shortages of food and water in the next few decades; they will likely reach the mid century mark with about the population as they now have.

The reduced supply of petroleum in future decades will also play a role in population growth. There will be many more field hands in industrialized countries as there will be less mechanized farming.

But hopefully, there will be new crops suited for the reduced supply of water in many agricultural areas. Climate change will shift our Midwestern wheat belt into Southern Canada. The prospects for big cities dwellers in parched U.S. states such as Nevada and Arizona are dismal.

Tomorrow and Tuesday evening the moon is full (exact time of full moon is in the 5:20 a.m. dawn of Tuesday). Tomorrow’s evening moon will be just off the teapot of Sagittarius. This early summer full moon has the lowest sky path of the year, reaching only a quarter of the way up in the South (from horizon to top of the sky).

Bob Doyle is available to present free Planetarium programs to camps and clubs. He is also interested in giving informal presentations to clubs on any topics treated in his columns including education, our civilization in future decades and various space issues (among them alien life prospects, Near Earth Asteriods and December 21, 2012). Leave a message at (301) 687-7799 or by email to Asteroids@frostburg.edu .