A Pew Research Center study shows that Muslims are projected to increase as an important share of Europe’s population, even with no future migration.

To see how the size of Europe’s Muslim population may change in the coming decades, Pew Research Center has modeled three scenarios that vary depending on potential future levels of migration. These are not efforts to predict what will happen in the future, but rather a set of projections about what could happen under different circumstances.

To give an example, between 25% and 30% of the population of Brussels, the “EU’s capital”, is Muslim, mostly first and second generation Moroccans and Turks, and some projections show that this could rise to 50% by 2050.

The baseline for all three Pew Research scenarios is the Muslim population in Europe (defined as the 28 EU countries, plus Norway and Switzerland) as of mid-2016, estimated at 25.8 million (4.9% of the overall population) – up from 19.5 million (3.8%) in mid-2010.

Even if all migration into Europe were to immediately and permanently stop – a “zero migration” scenario – the Muslim population of Europe still would be expected to rise from the current level of 4.9% to 7.4% by the year 2050. This is because Muslims are younger (by 13 years, on average) and have higher fertility (one child more per woman, on average) than other Europeans, mirroring a global pattern.

A second, “medium” migration scenario assumes that all refugee flows will stop as of mid-2016 but that “regular” migration to Europe will continue (i.e., migration of those who come for reasons other than seeking asylum). Under these conditions, Muslims could reach 11.2% of Europe’s population in 2050.

Finally, a “high” migration scenario projects the record flow of refugees into Europe between 2014 and mid-2016 to continue indefinitely into the future with the same religious composition (i.e., mostly made up of Muslims) in addition to the typical annual flow of regular migrants. In this scenario, Muslims could make up 14% of Europe’s population by 2050 – nearly triple the current share, but still considerably smaller than the populations of both Christians and people with no religion in Europe.

While Europe’s Muslim population is expected to grow in all three scenarios – and more than double in the medium and high migration scenarios – Europe’s non-Muslims, on the other hand, are projected to decline in total number in each scenario.

The Pew Research study says that taken as a whole, Europe’s population (including both Muslims and non-Muslims) would be expected to decline considerably (from about 521 million to an estimated 482 million) without any future migration. In the medium migration scenario, it would remain roughly stable, while in the high migration scenario it would be projected to grow modestly.

The impact of these scenarios is uneven across different European countries; due in large part to government policies, some countries are much more affected by migration than others.

The study says:

Countries that have received relatively large numbers of Muslim refugees in recent years are projected to experience the biggest changes in the high migration scenario – the only one that projects these heavy refugee flows to continue into the future. For instance, Germany’s population (6% Muslim in 2016) would be projected to be about 20% Muslim by 2050 in the high scenario – a reflection of the fact that Germany has accepted many Muslim refugees in recent years – compared with 11% in the medium scenario and 9% in the zero migration scenario.

Sweden, which also has accepted a relatively high number of refugees, would experience even greater effects if 2014 to mid-2016 migration levels were to continue indefinitely: Sweden’s population (8% Muslim in 2016) could grow to 31% Muslim in the high scenario by 2050, compared with 21% in the medium scenario and 11% with no further Muslim migration.

By contrast, the countries projected to experience the biggest changes in the medium scenario, such as the UK, tend to have been destinations for the highest numbers of regular Muslim migrants. This scenario only models migration of those who come for reasons other than seeking asylum.

And those countries with Muslim populations that are especially young, or have a relatively large number of children, would see the most significant change in the zero migration scenario; these include France, Italy and Belgium.

Some countries, such as Poland and Romania, would experience little change in any of the scenarios, typically because they have few Muslims to begin with and/or low levels of immigration.

The starting point for all these scenarios is Europe’s population as of mid-2016. The 2016 estimates are based on Pew Research Center analysis and projections of the best available census and survey data in each country combined with data on migration from Eurostat and other sources. Coming up with an exact count of Muslims currently in Europe, however, is not a simple task.

One source of uncertainty is the status of asylum seekers who are not granted refugee status. For the future population projections presented in this report, it is assumed that only Muslim migrants who already have – or are expected to gain – legal status in Europe will remain for the long term, providing a baseline of 25.8 million Muslims as of 2016 (4.9% of Europe’s population). However, Pew Research Center estimates that nearly a million additional Muslim asylum seekers who came to Europe in recent years will not have their applications for asylum accepted, based on past rates of approval on a country-by-country basis. If all of these Muslims who are currently in legal limbo in Europe were to remain in Europe, the 2016 baseline could rise to as high as 26.8 million, with ripple effects across all three scenarios.