Orthodox Christians have been declining as a share of the overall Christian population – and the global population – due to far faster growth among Protestants, Catholics and non-Christians, according to a new Pew Research Center report.

The figures show that over the last century, the Orthodox Christian population around the world has more than doubled and now stands at nearly 260 million, and that in Russia alone, it has surpassed 100 million, a sharp resurgence after the fall of the Soviet Union.

Yet today, overall just 12 per cent of Christians around the world are Orthodox, compared with an estimated 20 per cent a century ago. Of the total global population, four per cent of the total global population is Orthodox, compared with an estimated seven per cent in 1910.

The geographic distribution of Orthodoxy also differs from that of the other major Christian traditions in the 21st century, the Pew data show. Today, nearly four in five Orthodox Christians (77 per cent) live in Europe, a relatively minor change from a century ago (91 per cent).

But only around a quarter of Catholics (24 per cent) and one in eight Protestants (12 per cent) now live in Europe, down from an estimated 65 per cent and 52 per cent, respectively, in 1910.

According to Pew, Orthodoxy's falling share of the global Christian population is connected with demographic trends in Europe, where there are lower overall fertility rates and an older population than developing regions of the world, such as sub-Saharan Africa, Latin America and South Asia.

Meanwhile, Europe's population has long been shrinking as a share of the world's total population, and is projected in coming decades to decline in absolute numbers as well.

The largest Orthodox Christian population outside of Europe today is in Ethiopia, with the centuries-old Ethiopian Orthodox Tewahedo Church having an estimated 36 million adherents – nearly 14 per cent of the world's total Orthodox population. Orthodox Christians in Ethiopia are more religiously observant, by several common measures, than Orthodox Christians in Europe, Pew reported.

On religious observance furthermore, the lowest level comes from Orthodox Christians in the former Soviet Union, perhaps reflecting what Pew calls 'the legacy of Soviet repression of religion'. In Russia, just six per cent of Orthodox Christian adults say they attend church at least weekly, while 15 per cent say religion is 'very important' in their lives, and 18 per cent say they pray daily.

Orthodox Christians in the US, who make up roughly 0.5 per cent of the overall US population and include many immigrants, display 'moderate' levels of religious observance, lower than in Ethiopia but higher than most European countries, according to Pew. Around half (52 per cent) of Orthodox Christian adults in the US say that religion is very important to them, roughly one-in-three (31 per cent) report that they attend church weekly or more, and a slim majority say they pray daily (57 per cent).