As the latest statistics confirm, Canada is the most blessed place on earth, with a dynamic, diverse and relatively young population that will continue to grow until, by mid-century, we will rival some of the largest nations of Europe in size. We can thank three decades of enlightened government for these glad tidings – something to remember the next time we grumble about the fools on the Hill.

Skeptics of multiculturalism – and I'm looking at you, Maxime Bernier, Kellie Leitch and some other Conservative leadership candidates – should do themselves a favour and read through the latest batch of 2016 census data, released Wednesday.

Seniors outnumber children in Canada for the first time in this country's history. The reason that gets all the attention is the aging of the baby boomers. The more important reason, which is generally ignored, is that Canada's fertility rate (the average number of children per woman) is 1.6, half a baby short of the 2.1 children needed to keep a population stable.

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Read more: 2016 census: Canada's seniors outnumber its children for first time in history

Nonetheless, Canada's population grew by 5 per cent between 2011 and 2016, and will continue to grow in the coming decades, reaching 50 million by 2060, thanks to three decades of robust immigration. Back in 1992, Brian Mulroney's government set a target of 250,000 new arrivals a year. Jean Chrétien and Paul Martin generally maintained those levels. Stephen Harper increased them slightly and Justin Trudeau has increased them further still, to 300,000 immigrants and refugees each year. The result, as everyone knows, is that one Canadian in five today was not born in Canada.

This puts us at odds with most developed and many developing countries. By 2060, Canada will have about the same population as Italy, which will have declined from today's 60 million to just over 50 million, according to the United Nations Population Division. A reluctance to accept consistently high levels of immigration, combined with low fertility rates, is hollowing out Europe's population. Some particularly xenophobic Eastern European countries will suffer the most. Bulgaria will lose half its population between now and 2060.

But Europe is not alone. By 2060, Japan's population will be in free fall, having gone from just under 130 million to just over 100 million, on its way to about 80 million by the end of the century. South Korea, Singapore and Thailand will all be losing population. In terms of sheer numbers, China will experience the most severe losses, swooning from a peak of 1.4 billion around 2030 to 1.25 billion by 2060. That's 150 million missing people.

Many demographers believe that national population declines will arrive earlier, and be more severe, than UN projections.

All these people not born will ease strains on the environment. But they will pose economic challenges, as increasing life expectancy and reduced fertility undermine health care and pension systems. A shortage of young couples with children will reduce the market for housing, appliances, diapers. Labour shortages will increase, though productivity will improve to compensate.

Some people believe the solution to population decline is to encourage women to have more babies. But despite aggressive efforts in Sweden, Singapore and elsewhere, no government has succeeded in restoring the fertility rate to 2.1. And if you think about it, trying to bribe a woman to have a third child in the national interest is offensive.

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Immigration alone isn't the answer to population decline. Unless the native population honestly embraces multiculturalism, immigrants may fail to integrate, settling into impoverished and resentful ethnic enclaves – something we also see in parts of Europe.

Canada has largely avoided this trap by bringing in new Canadians from around the world rather than mostly from just one region, ensuring genuine diversity.

But this magic mix of high levels of immigration and multicultural diversity must always be defended and explained. The United States should also grow its population in the coming decades – by the end of this century the population of China could be less than twice that of the United States – but President Donald Trump is putting that future at risk in his efforts to close American borders and minds.

Every day we must make the case for a more multicultural Canada. We must agree to do this together. The alternative is stagnation and decline.