Pope Francis often makes shocking statements. He has shared liberal views about gender and sexuality. He claims atheists can go to heaven. He has even suggested that pets have an afterlife.

This latest statement is just as dramatic. 

Speaking to the public, the PontiffAnother term for the Pope. It derives from the name for the highest ranking priests in the In ancient Roman religion, each devoted to a different god. blasted pet owners who refuse to have multiple children, labelling them "selfish".

Francis' concerns reflect a much wider issue. Although the world population is rising, birth rates in many countries are falling. And this decline will soon become global. 

For the Pope, the problem is close to home. By 2100, Italy's population is expected to shrink from 61 to 28 million. By 2050, the Italian death rate will be twice its birth rate. Demographers are predicting the same problem in at least 22 other countries, including Japan, Spain and Thailand.

There is also a falling fertility rate worldwide. Between 1950 and 2020, this sank from 4.7 to 2.4. In the same timeframe, life expectancy has increased from 45.7 to 72.6 years. Fewer people are being born but those alive are living longer.

Many agree with Francis that these two trends threaten a crisis. As the number of old people grows, the young will have to work harder and pay more to care for them. This could have devastating effects on economies. 

For writer and researcher Robert Colvile, it is already causing problems. The UK, he says, "is turning into an elderly care system with a state attached." The young might become the servants of the old.

Others disagree. Better healthcare might allow elderly people to remain active for longer. And a smaller population could make everyone richer. 

David Attenborough, Miley Cyrus and Prince Harry have all argued that stopping further growth will help save the planet.

Others claim that we should control and reduce the world population. The Earth is past full. Any growth will make our lives worse.

Improvements have often come alongside a growing population. Poverty has decreased as populations grow. 

The human population has always grown. We have never had an overall decline before. The results, whatever they are, will be huge.

Yes, say some. For centuries, population growth has walked in step with better lives. A population decline might lead to the opposite.

No, say others. A smaller population will give each person more space, food and water, and will reduce our effect on the environment.

Or, says a third view, population decline is something to take as it comes. Whether it changes things for the good or the bad is up to us.