A great deal has appeared recently in our media about climate change and its destructive consequences; rising sea levels, bigger and more frequent storms of every description, and seemingly unstoppable wildfires. Granted there persists a number of climate change deniers. Some are loud – shrill even. Almost none are scientists. People who study changes in the climate, aka scientists, have pretty much coalesced around the belief that most of the increases in global temperatures in the last century have been caused by human activity.
Much of the reporting on climate change focuses on the burning of fossil fuels. That is the main source of greenhouse gases in the atmosphere. What is not often reported is the inevitable relationship between increasing greenhouse gas emissions (carbon dioxide and methane) and an unprecedented rise in human population. We tend not to harp on that too much because people are probably not going to significantly slow their rate of reproduction, at least not anytime soon.
The past century has seen a rise in the average global temperature of about 1 degree Celsius accompanied by a six-inch rise in sea levels. The 37-year period between 1950 and 1987 saw the fastest doubling of human population in history, from approximately 2.5 billion to 5 billion.
Fortunately for us, and the planet, the rate of population growth appears to be leveling out somewhat. This has been attributed to a decline in fertility rates, which has only a little to do with an individual’s ability to reproduce, except for the fact that the population has been steadily aging itself out of the reproductive years. The global average lifespan is now about 73 years, and the global median age has risen from 22 years in 1970 to 31 years now.
More telling reasons for the slowing of population growth (fertility rates) are increases in the education and empowerment of women, effective methods of birth control, and more women in the workforce. In the pre-modern era fertility rates were typically as high as 4.5 to 7 births per woman. An Our World in Data report recently printed, “As health improves and mortality rates decrease, we typically see an accelerated population growth. This rapid population growth then comes to an end as fertility rates decline and approach two children per woman.”
Even with the slowdown our population is still growing, albeit at less than the bunny rabbit pace of the 1950s through the mid-1980s. United Nations data analyzed by the Pew Research Center predicts that humans could number about 10.9 billion by the year 2100. If you go all the way back to the 1800 estimate of 1 billion, that amounts to a whopping increase in less than three centuries.
Even if we can achieve a net zero gain in population, can the planet sustain 10 or 11 billion people indefinitely? If the answer turns out to be no, then that will raise an even bigger question because few people will be altruistic enough to line up every so often to jump off the edge of the world. The answer has to be a greater emphasis on birth control combined with a continued quest for cleaner energy practices.
The emphasis on birth control sounds easy enough if you say it real fast, but the idea goes against some deeply held religious and cultural beliefs. Not many parents want teachers telling their students how many kids they should have when they grow up. That’s a hard sell. And maybe the planet can sustain the current population and even the current growth rates. If not, then it’s going to be awkward in the near future to get caught with our pants down.
Temperature and sea level information is from NASA data. The population, aging and fertility rate numbers are from reports in Our World in Data. The 2100 population predictions are from United Nation data analyzed by the Pew Research Center. All these numbers are estimates subject to change with new research, and different data is certainly out there.