ARE Muslims taking over the world, or at a minimum, transforming Europe into Eurabia? Whatever your hopes or fears for the future of the world's religions, a report published this week has plenty to stoke them. “The Future of the Global Muslim Population”, produced by the Pew Research Centre, a non-profit outfit based in Washington, DC, reckons Muslim numbers will soar from 1.6 billion in 2010 to 2.2 billion by 2030. In other words, from 23.4% to 26.4% of the global total.

At the heart of its analysis is the ongoing effect of a “youth bulge” which peaked in 2000. In 1990 Islam's share of the world's youth was 20%; in 2010, 26%. In 2030 it will be 29% (of 15-to-29-year-olds). But the Muslim world is slowly heading towards paunchiness: the median age in Muslim-majority countries was 19 in 1990. It is 24 now, and will be 30 by 2030. (For French, Germans and Japanese the figure is 40 or over.) This suggests Muslim numbers will ultimately stop climbing, but later than the rest of the world population.

The authors call their calculations demographic, not political. Drawing on earlier Pew research, they say conversion is not a big factor in the global contest between Islam, Christianity and other faiths; the converts balance out. Nor do they assess piety; via the imperfect data of the United Nations, the European Union and national statistics, they aim simply to measure how many people call themselves Muslim, at least culturally, if asked.

New numbers, they say, will change the world map. As Indonesia prospers, its birth rate is falling; South Asia's remains very high. By 2030, 80m extra mouths in Pakistan will boost its Muslim numbers to 256m, ousting Indonesia (with 239m) as the most populous Islamic land. India's Muslim minority will be nearly as large at 236m—though growth is slowing there too. And in 2030 India's Muslims will still constitute only a modest 15.9% of that country's swelling total, against 14.6% now.

The report asserts no causal link between Islamic teaching and high fertility rates, although it notes that poverty and poor education are a problem in many Muslim lands. In Muslim countries such as Bangladesh and Turkey, it observes, the lay and religious authorities encourage birth control. Better medical care and lower mortality boost poor-country population numbers too.

Some bleak findings concern Nigeria, where Muslim numbers are seen rising to 117m in 2030 from 76m now, edging up from 47.9% to 51.5% of the population. Illiteracy among Nigerian women of child-bearing age is three times as high among Muslims (71.9%) as among others (23.9%). Two-thirds of Nigerian Muslim women lack any formal education; that goes for just over a tenth of their non-Muslim sisters. The fertility rate is between six and seven children per Muslim woman, versus five for non-Muslims. It is hard to prove that these factors are related, but they do seem to form a pattern.

Eurabian nights

The total Muslim share of Europe's population is predicted to grow from 6% now to 8% in 2030: hardly the stuff of nightmares. But amid that are some sharp rises. The report assumes Britain has 2.9m Muslims now (far higher than the usual estimates, which suggest 2.4m at most), rising to 5.6m by 2030. As poor migrants start families in Spain and Italy, numbers there will rocket; in France and Germany, where some Muslims are middle-class, rises will be more modest—though from a higher base. Russia's Muslims will increase to 14.4% or 18.6m, up from 11.7% now (partly because non-Muslims are declining). The report takes a cautious baseline of 2.6m American Muslims in 2010, but predicts the number will surge by 2030 to 6.2m, or 1.7% of the population—about the same size as Jews or Episcopalians. In Canada the Muslim share will surge from 2.8% to 6.6%.

How will liberal democracies accommodate such variety? The clarity of a written constitution may give America an advantage over many European countries, where unwritten custom has more sway. Jonathan Laurence, an Islam-watcher and professor at Boston College, thinks Europe could rise to the challenge, but failure is also easy to imagine. Europe's Muslims should, by 2030, have become articulate and effective political bargainers. But with nativism on the march, it is also highly possible that Muslims will come to feel they have less in common with their fellow citizens than with their growing band of co-religionists elsewhere.