Booming population growth in regions where child marriage and female genital mutilation are common threatens to undermine progress on tackling both abuses, which blight the lives of hundreds of millions of girls, experts say.
The number of girls mutilated is likely to soar and there will be no decline in child marriage unless the world dramatically scales up action, the U.N. children's agency UNICEF said ahead of an international summit on FGM and child marriage on Tuesday.
Worldwide, more than 130 million girls and women have undergone FGM and more than 700 million women alive today were married as children. Of these more than a third were married before they turned 15.
"The numbers tell us we must accelerate our efforts. And let's not forget that these numbers represent real lives," said UNICEF Executive Director Anthony Lake. "We can't let the staggering numbers numb us - they must compel us to act."
The populations of some countries in sub-Saharan Africa are expected to double or triple within a generation.
Data released by UNICEF shows that by 2050 nearly one in three births will occur in the 29 countries in Africa and the Middle East where FGM is most common.
The number of women married as children in sub-Saharan Africa is likely to double by 2050 and the region will overtake South Asia in having the largest number of child brides.
FGM, which involves the partial or total removal of the female genitalia, causes a host of physical and psychological problems and has been internationally condemned as a gross human rights abuse.
Child marriage deprives girls of education, traps them in poverty and increases the chance of dangerous or fatal childbirth complications. Child brides are also more likely to be victims of sexual and domestic abuse.
"FGM and child marriage profoundly and permanently harm girls, denying them their right to make their own decisions and to reach their full potential," said Lake.
"Girls are not property; they have the right to determine their destiny. When they do so, everyone benefits."
An adolescent girl today is about a third less likely to undergo FGM than she would have been 30 years ago. However, even if this rate of decline is kept up, the impact of population growth means up to 63 million more girls could be cut by 2050, UNICEF data shows.
Even if the rate of decline doubles, the number of girls and women affected by FGM will remain roughly at today's levels.
On child marriage, even if rates of decline seen in the past three decades are sustained, the number of women married as children will remain the same in 2050 as they are today.
Lake said solutions must be driven by communities, families and girls themselves to change mindsets and break the cycles that perpetuate FGM and child marriage.
Surveys show that nearly two thirds of people in countries affected by FGM think the practice should stop, but many families continue cutting their daughters because of strong social pressure.
UNICEF said encouraging public discussions about FGM would help expose hidden attitudes in favour of abandoning the practice which would hasten its demise.
Data from some countries reveal a more positive picture. Ghana, for example, is on course to virtually eliminate FGM by 2030 and it should be possible to end the practice in Kenya within a generation.
However, the picture looks bleak in countries like Somalia where FGM is almost universal and Mali where nearly nine in ten girls are cut.
Somalia's female population is expected to more than double by 2050 and Mali's will nearly triple, meaning millions more girls will be subjected the practice.
Editing by Ros Russell, firstname.lastname@example.org