More than 100 science academies around the world have called on world leaders to take action on population and consumption at the Rio+20 summit.
They say past failures on these issues threaten the natural world and prospects for future generations.
The science academies include the UK's Royal Society as well as its peers in countries at all stages of development.
Preparatory talks for next week's summit have opened but sources report slow progress on unresolved issues.
The science academies' public declaration is particularly notable as experts in both developed and developing countries have joined forces on what used to be a divisive topic.
"The overall message is that we need a renewed focus on both population and consumption - it's not enough to look at one or the other," said Prof Charles Godray from the Martin School at the University of Oxford, who chaired the process of writing the declaration.
The developed world is mainly responsible for the world's record consumption levels, the scientists also said that the global population is currently around seven billion, and most projections suggest that it will probably lay between eight and 11 billion by 2050.
"Global consumption levels are at an all time high, largely because of the high per-capita consumption of developed countries."
If the billion poorest people are to have adequate access to food, water and energy, the academies say, developed countries will have to reduce their own consumption of natural resources.
They say this can be done without reducing prosperity so long as different economic models are followed.
Failing to make these changes "will put us on track to alternative futures with severe and potentially catastrophic implications for human well-being".