From the following NatGeo article's comment section:
"[...] Using biochar for fertilizer instead of chemicals increases food output by almost 800%, and biochar is not even the best organic method for increasing production. Read Fred Pearce's The Coming Population Crash, in which he proves that the trends are already locked into place that will reduce the global population by about 4 billion during the next 30 years without any draconian measures, panic or government programs." (Rod Van Mechelen)
I've never heard of biochar (neither did the reader who replied to Van Mechelen) or Fred Pearce and I won't take the time now to look into his argument, but it would present a striking contrast to the population estimates from mainstream demographers, which, from the excerpts I feature from the NatGeo article, are in considerable disagreement.
As World’s Population Booms, Will Its Resources Be Enough for Us?
New projections of escalating growth increase the tension between humanity’s expanding needs and what the planet can provide.
By Dennis Dimick, National Geographic
PUBLISHED SEPTEMBER 21, 2014
There are more than 7 billion people on Earth now, and roughly one in eight of us doesn't have enough to eat. The question of how many people the Earth can support is a long-standing one that becomes more intense as the world's population—and our use of natural resources—keeps booming.
We've been on a big growth spurt during the past century or so. In 1900, demographers had the world's population at 1.6 billion, in 1950 it was about 2.5 billion, by 2000 it was more than 6 billion. Now, there are about 7.2 billion of us.
In recent years we've been adding about a billion people every 12 or 13 years or so. Precisely how many of us are here right now is also a matter of debate, depending on whom you consult:The United Nations offers a range of current population figures and trends, the U.S. Census Bureau has its own estimate, and the Population Reference Bureau also tracks us.
The new UN study out this week projects that the world's population growth may not stop any time soon. That is a reversal from estimates done five years ago, when demographers—people who study population trends—were 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 declines—or a reduction in the number of children per mother—in most parts of sub-Saharan Africa that are still experiencing rapid population growth. As Rob Kunzig wrote for National Geographic, the new study estimates that "there's an 80 percent chance . . . that the actual number of people in 2100 will be somewhere between 9.6 and 12.3 billion."
Measuring Our Rising Impact
As a result of this massive expansion of our presence on Earth, scientists Ehrlich, John Holdren, and Barry Commoner in the early 1970s devised a formula to measure our rising impact, 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 resources each person uses. The graphic above, which visualizes IPAT, shows that the rise in our cumulative impact since 1950—rising population combined with our expanding demand for resources—has been profound.
IPAT is a useful reminder that population, consumption, and technology all help shape our environmental impact, but it shouldn’t be taken too literally. University of California ecologist John Harte has said that IPAT ". . . conveys the notion that population is a linear multiplier. . . . In reality, population plays a much more dynamic and complex role in shaping environmental quality."
One of our biggest impacts is agriculture. 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 new 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 the 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."