The world population surpassed 8 billion in November, according to an estimate by the United Nations.

The evolution of human civilization has been the driving growth of the global population. Technological progress has led to increased food production and made more land and resources available for use.

Big waves of innovation such as the beginning of agriculture and the Industrial Revolution have accelerated population expansion.

Optimists may predict a bright future where people can obtain the things they need more efficiently, thanks to a major spurt of technological innovations, while food and energy will be shared more efficiently to sustain a smaller population.

But clearly there are limits to both the biological resources the Earth can produce and the underground resources that can be developed for consumption.

How many people could this planet sustain now?

EARTH’S ABILITY TO SUSTAIN HUMAN LIFE

There is one indicator that measures the overall environmental impact of the human race. The indicator, called the “ecological footprint,” has been developed and promoted by researchers from Canada and other countries.

The metric tracks the use of productive surface areas including farmland, forests and fishing grounds through economic and other human activities.

Using statistical data, the indicator also factors in the areas needed to produce food and clothing and to absorb the waste we generate, especially our carbon emissions from burning fossil fuels. The indicator shows whether the people on the Earth live within the limits of the productivity of its ecological assets.

According to the Global Footprint Network, an international environmental organization, in 1961, when the global population was slightly over 3 billion, the people in the world needed the regenerative capacity of 0.7 of the Earth to provide the natural resources and ecological services they used. The figure surpassed 1 in 1971 and stands at 1.8 now.

If everyone lived and consumed like the average Japanese, mankind would need at least 2.9 planets to sustain this lifestyle. The comparative figures for the Americans, the Chinese and the Indians are 5.1, 2.4 and 0.8, respectively.

A wealthier lifestyle means more consumption per person. Air travel requires more fuel than traveling by rail or ship over the same distance. Producing beef or pork demands more resources than growing grains. The ecological footprint, of course, is not an absolute measure.

But it shows how wealthy and convenient lifestyles impose heavy burdens on the future.

GROWING SENSE OF CRISIS

At the COP15 U.N. biodiversity summit held in Canada in December last year, countries agreed on a set of new goals to halt the destruction of the Earth’s ecosystems, including protecting 30 percent of the planet for nature by 2030, a goal known as “30-by-30.”

The agreement on these tough goals reflects a growing sense of crisis among nations about the degradation of the environment.

Consumption of fossil fuels and the consequent harmful climate change also impose a serious strain on the Earth. So does cutting down forests to create cropland for food production.

During its 4.6-billion-year history, the Earth has experienced five mass extinction events, including the last one that occurred 65 million years ago and wiped the dinosaurs from existence. Scientists now believe that we are in the midst of a sixth mass extinction.

Currently, the species extinction rate is estimated to be far higher than the rate during the previous mass extinction event. Of the estimated 8 million species on the Earth, about 1 million are currently on the brink.

Species are vanishing at a rate tens or hundreds of times faster than the average for the past 10 million years. Humanity is destroying the planet at a horrifying pace.

TOWARD A RECYCLING-ORIENTED SOCIETY

If the destruction of nature reaches a certain tipping point, recovery would become impossible, threatening the prosperity of mankind.

The concept of “planetary boundaries” shows a threshold for the Earth’s nine key bio-physical subsystems or processes, thresholds that, if we cross, could push the Earth’s natural system into a completely new state, one which might not support humanity.

Four of the nine planetary boundaries are feared to have already been crossed: biodiversity integrity, biogeochemical flows of nitrogen and phosphorus, climate change and land-system change. That means planetary boundaries for a safe operating space for humanity may have been overstepped.

Nitrogen and phosphorus are used as fertilizers to boost food production. But excessive use of these chemicals cause serious pollution of rivers and seas.

The global population is projected to top 10 billion in the 2050s and peak at 10.4 billion in the 2080s. Even if we assume that the number of people living on the Earth continues declining after that toward a stable and sustainable population, we must ask ourselves whether we can avoid crossing the planetary boundaries to ensure the long-term sustainability of humanity.

We need to work together to tackle common global challenges for all countries one by one while reconsidering our social systems and lifestyles for long-term sustainability. We need to build a recycling-oriented society for our own future, not just for the Earth or nature.

As we have passed the 8-billion landmark for the global population, we should reflect anew on the health of the planet and our own lifestyles to think about what we could and should do to leave behind a livable Earth to our offspring.

The Asahi Shimbun, Jan. 10