The answer is: everything.
Sustainable development is about meeting the needs of the present without compromising the ability of future generations to meet their own needs. The track we are currently heading down, by ignoring reproductive rights, means that it is extremely unlikely any generation after us will be able to meet their basic requirements.
We are condemning future generations to live in increasing levels of poverty.
The earth's population is growing at an alarming rate. By 2050, it's predicted the global population will reach nine billion people. Our planet's resources simply cannot cope with adding the equivalent of China and India.
The term "population control" is loaded with associations to atrocities committed in the name of ethnic cleansing, eugenics and contempt for the poor.
But Dr Carmen Barroso, of the International Planned Parenthood Federation, believes that it's imperative to talk about it. "As long as women are not empowered to decide when and how many children they have, they will not lead sustainable lives. And as long as women do not live sustainable lives, there is no sustainability," she said.
Dr Barroso is not advocating practices like forced sterilisation. She wants to empower women to control their own sexual and reproductive health. "Comprehensive family planning is the most effective form of population control," she says.
95% of the world's population growth occurs in areas already struggling with illiteracy, poverty, and civil unrest. More growth means more people living with these hallmarks of extreme poverty.
At present we use and degrade the world's resources at an unsustainable level. An extra two billion people can only worsen this.
The UN's Millennium Development Goals (MDG 5A and 6B) recognise empowering women as the single greatest factor in the development of communities, leading to greater employment, better health and nutrition for families, and increases in social status and income. Most importantly, the more women are educated, the fewer children are born and the older they are when they first become mothers.
There are currently 215 million women in the world who lack access to basic reproductive healthcare. Millions more are without due to lack of education, funding and distribution; or for cultural, social and religious reasons which prevent them from accessing sexual health services.
At the current rate of population growth we have no hope of achieving sustainable development. But, there are solutions. Over 100 academies of science have called for the UN to mandate and develop comprehensive population solutions.
Family planning is the most cost-effective method of encouraging sustainable development. For every dollar spent on family planning, six times that is saved, which can then be spent on other development programs.
Joan Castro, of the Global Health Population and Environment Alliance, is particularly passionate about youth access to sexual and reproductive health. Youth sexual health and education is especially pertinent in developing countries, where up to a quarter of women are mothers before age 18. "If young people are the stewards of the environment, they should be able to be the stewards of their own sexuality," says Castro.
Given the statistical evidence in favour of educating and empowering women to make informed choices about their sexual health, and the MDGs on making sexual healthcare universally available, one would think that the UN would embrace sexual health unanimously.
This is not the case: all reference to "reproductive rights" have been cut from the draft outcome text.
The Vatican's representative to the UN is vehemently opposed to mentions of reproductive rights. Technically only a "permanent observer state", the Vatican has proposed over eighty amendments and deletions in the sections of the text relating to gender, health and education; making it one of the most stubborn "countries" in Rio overall. Several states of the G77 group of developing nations have splintered to join the Holy See's position.
When sections of the text mentioning "universal access to reproductive health," and "family planning and sexual health" were agreed upon by all but the Holy See, the UN - who make decisions by consensus - had no choice but to change the text or delete it.
When developing countries, vulnerable to negative events of population growth, side with the Holy See it is a testament to the power of religious and traditional objections to women's rights and family planning.
We proceed from Rio+20 with no international safeguarding of reproductive rights. Instead of the UN, we must look to communities to guarantee healthcare to those in need.
In the words of Dr Joan Castro, whose PATH Foundation delivers family planning to thousands, despite the Philippines' Family Planning Act being stuck in the upper and lower houses of government for nearly ten years: "just because we don't have a family planning policy doesn't mean we can't have family planning."
Hopefully more nations will realise this in future, as the UN process isn't doing much to help them along.
By Genevieve Stewart, photo by Madeline Snow.
Follow Genevieve Stewart on Twitter: www.twitter.com/gen_stewart