The world's science academies on Thursday warned the upcoming Rio Summit that Earth faced a dangerous double whammy posed by voracious consumption and a population explosion.

The warning was issued by 105 academies ahead of the June 20-22 UN conference on sustainable development, where leaders will debate the planet's worsening environmental health and its entrenched poverty.

The signatories include the paramount scientific academies in North America, Europe and Asia.

"Increasing population growth and unsustainable consumption together pose two of the greatest challenges facing the world," their statement said.

"Current patterns of consumption, especially in high-income countries, are eroding natural capital at rates that are severely damaging the interests of future generations," it said.

Earth's population is expected to roughly triple by 2050 compared to a century earlier.

It stood at three billion in 1950, reached seven billion in 2011 and is likely to reach about 9.5 billion by 2050 -- a rise that will occur especially in the poorest countries, according to UN estimates.

"Rapid population growth can be an obstacle to improving standards of living in poor countries, to eliminating poverty and to reducing gender inequality," the joint statement said.

It emphasised the need to help millions rise out of poverty, brake trends of reckless consumption and address population growth through voluntary means such as education for women and access to contraception.

"If the right conditions are in place, measures that reduce fertility rates while respecting human rights can stimulate and facilitate economic development, improve health and living standards, and increase political and social stability and security," it said.

About 115 heads of state and government are expected for the conference, which marks the 20th anniversary of the Rio Earth Summit that placed the environment on the world's political agenda.

The meeting will hear grim news about the state of the environment, ranging from an alarming increase in climate-altering greenhouse gases to depletion of the oceans and deforestation.

Scientists have become increasingly outspoken about population growth, saying it has an obvious role in environmental damage and exposing countries to the risks of drought, floods and storms.

Yet the issue is often dormant or sidelined in international politics.

The summit will cap more than a week of meetings gathering as many as 50,000 activists, business executives and policymakers.