The figure on the World Population Clock yesterday was mesmerising. For the first time, there were more than 8,000,000,000 people on our planet.

There are many other startling figures. It is only 11 years since the world's population reached 7 billion. The UN believes it will hit 9 billion by 2037 and 10.4 billion by the 2080s.

India has 180 million more people than it did a decade ago, taking it to nearly 1.42 million. It is expected to replace China (now on 1.45 billion) as the most populous country in the world next year. 

There are fears that the number of people in sub-Saharan Africa46 countries lie south of the Sahara desert. 95% of all deaths from malaria occur here in this region. will increase by 95% over the next 30 years.¹

But the picture is not clear-cut, because the rate of growth has slowed. This is thanks to the increased use of contraception, and better education and more jobs for girls and women.

Because of this, some very different results have been predicted. Researchers at Washington University believe that the world's population will peak at 10 billion in 2064 and drop to 9 billion by 2100.

But some countries see this as bad news. People are generally living longer after they retire - so need more young people to look after them.

China, which only allowed families to have to one child between 1980 and 2015, is now encouraging them to have three children.

Climate campaigners, however, argue that every extra person puts a further strain on Earth's resources. They say that the biggest single thing you can do for the planet is not have children.

Food production puts huge pressure on the environment. Almost 40% of the world's land surface is used to meet the needs of humans and livestock.²

In 1994 researchers from Stanford University in California worked out that the ideal size of our species would be between 1.5 and 2 billion people.

Yes: Many live in overcrowded places without enough to eat. And the demands on the planet are huge: between 1970 and 2020 the wildlife population fell by two thirds, while the human population doubled.  

No: The problem is not the number of people but the resources they use up. If we can all learn to live more frugally - particularly the richest people, who consume most - the planet need not suffer.

Or... We should not be focusing on the world, but on the whole solar system, as Jeff Bezos has suggested. If we can colonise Mars and other planets, there will be plenty of room for everybody.

Sub-Saharan Africa - 46 countries lie south of the Sahara desert. 95% of all deaths from malaria occur here in this region.