The world's population is increasing and its birth rate is falling.

South Korea already had the world's lowest birth rate.

But this week, new data showed it had fallen further.

Japan also recorded a new low.

The decline of births is in a state of crisis.

I believe we are at a time when we have to take urgent measures.

The birth rate is the average number of children that each woman has and when birth rates are discussed, you'll see this number a lot: 2.1.

This is the birth rate needed to maintain population levels.

South Korea's not close.

Last, year, its rate was 0.72.

Japan is at 1.26.

To put this in context, the EU average is 1.53 and the UK is at 1.49 and that is a record low.

In fact, many countries are now below 2.1.

Even countries with relatively high birth rates are often at half the birth rate of what they were.

And the average person now lives in a country in the world that has a lower than replacement fertility rate.

And birth rates matter because they contribute to long-term changes in our populations, and the consequences that follow.

Low birth rates can cause populations to fall.

Japan's is expected to decrease by 30% by 2070.

South Korea is to halve by the end of the century.

In some countries including the UK, the situation is different.

Populations are projected to increase mainly because of immigration.

But immigration can't counter all the impacts of a low birth rate.

There is no quick fix, there is no one fix to population decline or population aging.

So birth rates affect population growth in the long run.

Whereas immigration can affect in the short run, but immigrants also age.

And as people live longer, combined with low birth rates, elderly people will make up a greater proportion of the population as we've seen in Japan.

It's no surprise that Japan, which has had this very, very long, very low fertility rate and the oldest population in the world has got the worst government finances in the developed world.

Because the government is indeed spending more and more on healthcare and pensions and has fewer and fewer taxpayers.

If that's Japan, in the UK, a shift in the makeup of the population is coming.

By 2070, the number of workers is projected to rise by a million.

The number of pensioners will rise by 5 million.

This will inevitably create pressures.

The economist argues that for countries with low birth rates, the implications are higher taxes, later retirements, lower real returns for savers and possibly government budget crises.

We'll see.

But there's no doubt some governments are increasingly preoccupied with low birth rates and what's causing them.

In South Korea, there are many reasons including the cost of education and expectations of women in the workplace.

Childcare is a consideration too just as it is in the UK.

According to a recent international study, the UK has some of the highest childcare costs in the world.

There's also a shortage of places.

And around the world, the availability of childcare impacts women's decisions.

Research really shows that if you have affordable high quality early childhood education, good daycare for everybody, that is associated with higher birth rates.

This helps explain what's happening.

But by the admission of those who study birth rates, fully explaining what's happening is hard, and it makes responding to low birth rates hard too.

It's difficult for policymakers to address the complexity of the cultural reasons why we are not having as many children.

What really they have in their arsenal is only economic tools and it goes well beyond that.

It's difficult for policymakers but some are acting.

In South Korea, they tried cash incentives and subsidized health care as we've seen that didn't work.

In France in January, President Macron talked of demographic rearmament and announced a plan that includes changes to parental leave.

Or in Italy, which has one of the lowest birth rates in Europe, Prime Minister Maloney has announced a range of initiatives.

But evidence suggests it's very difficult to reverse a falling birth rate, and while some countries try, the global population continues to go up.

And the UN highlights two factors to explain this: the gradual increase in human lifespan and high and persistent levels of fertility in some countries.

There are those to whom this global population growth is the real issue in particular for our climate and who believe low birth rates are welcome.

But as we've seen already, many countries have low birth rates and some want to increase theirs.

Population growth and low birth rates are both demanding attention.

A lot of people are surprised to see that the global population numbers are still growing. The total number of people on the planet, at the same time that we keep talking about birth rates declining.

And I like to think of it as what's on the surface versus what's beneath the surface.

And beneath the surface, those declining birth rates will cause major shifts in the nature of our populations.

Shifts that may lead the global population to start falling in the next century; shifts that for better or worse will have consequences for how our societies function.