Twenty years after the 1992 Earth Summit -- which put the issue of sustainable development into the public spotlight, and produced two legally binding, if widely ignored treaties, plus important agreements such as Agenda 21 -- world leaders are returning to Rio de Janeiro to take another shot at sustainable global development.

Expectations for this year's Rio+20 Summit are far more modest than they were for the 1992 Earth Summit.

This is a year of transition in many countries, with elections or leadership changes in the U.S., Mexico, Russia, China, France and elsewhere that are concentrating on national circumstances. At the same time, many parts of the world remain preoccupied with the financial and economic crisis, which is encouraging more short-term thinking and a reduced focus on the long term.

Many key leaders will be absent from the Rio+20 Summit, including U.S. President Barack Obama, German Chancellor Angela Merkel and UK Prime Minister David Cameron.

In many ways, this is not the best time for a major global gathering on sustainable development, Yvo de Boer, KPMG's special global advisor on climate change and sustainability, said in a recent report.

What is Rio+20?

The three-day (June 20-22) United Nations Conference on Sustainable Development -- its nickname honors the 20th anniversary of the 1992 U.N. Earth Summit in Rio -- aims to advance prospects for global sustainable development.

According to the U.N., the world now has 7 billion people -- by 2050, there will be 9 billion. One out of every five people (1.4 billion) currently lives on $1.25 a day or less. A billion and a half people in the world do not have access to electricity. Two and a half billion do not have a toilet. And almost a billion go hungry every day.

Rio+20, the biggest U.N. conference in years, will draw an estimated 50,000 people from 190 countries, including heads of state and government along with thousands of participants from the world body and its agencies, civil society and the private sector. Over its three days, the conference will feature more than 550 side events organized by the U.N. itself as well as events and presentations by nongovernmental organizations such as environmental advocacy groups.

The summit will focus on two themes: a green economy, in the context of sustainable development and poverty eradication, and an institutional framework for such development.

Seven key areas have been identified by the U.N. as needing urgent attention: creation of jobs, access to energy, building sustainable cities, ensuring food security and sustainable agriculture, access to water, managements of oceans and disaster readiness.

The intended outcome of the conference is an action plan to be adopted by world leaders, entitled The Future We Want. This action plan will be a focused political document designed to ensure coherent international action through voluntary national commitments.

It's never an easy task to gain consensus among almost 200 nations. The negotiations around the wording of the Rio+20 commitments have been prolonged and complex.

Preliminary discussions created a well-received zero draft document that had been trimmed from several hundred pages to a more manageable 20 pages by the end of 2011. However, in recent months the draft has grown again to around 80 pages.

What Did The 1992 Summit Achieve?

Comparisons are inevitably drawn between the 2012 Rio+20 Summit and the Rio Earth Summit in 1992.

Three agreements and two legally binding conventions were agreed at the 1992 Earth Summit:

Agreements. Agenda 21, which is a comprehensive action plan for achieving sustainable development worldwide. The number 21 refers to an action plan for the 21st century; Rio Declaration on the Environment and Development, which is often abbreviated to The Rio Declaration. This agreement comprised 27 wide-ranging principles defining the rights and responsibilities of states; Statement of Forest Principles, which intends to provide the foundation for sustainable management of forests worldwide.

Conventions.The United Nations Framework Convention on Climate Change (UNFCCC), an international treaty that led to binding greenhouse gas (GHG) emission targets for industrialized countries (the Kyoto Protocol); The Convention on Biological Diversity (CBD) is a legally binding treaty with three main goals: to conserve biodiversity on the Earth, to ensure sustainable use of its components, and to ensure fair access to ecosystem and biodiversity resources.

These treaties and agreements created or accelerated many sustainability initiatives and concepts that most businesses today are familiar with: from carbon credits and trading to industry sector sustainability frameworks and international efforts to address forest loss and dwindling fish stocks. As such, the Earth Summit in 1992 arguably changed the world and the way we do business, according to a KPMG report.

A Big Shoe To Fill? Or Not?

Experts have voiced skepticism that this year's event will lead to anything substantial.

Some point to the fact that, this time around, there are no grand treaties on the table that promise to result in international law. Instead, commitments made at Rio+20 will be voluntary and differentiated to take account of variations in development status and economic and social capacity.

Others argue that this year's summit will not amount to much simply because there's no shoe to fill. The 1992 Earth Summit hasn't been well implemented.

Twenty years ago, the atmospheric carbon dioxide concentrations were 357 parts per million. Today they average 395 parts per million (ppm) and readings of 400 ppm have been observed in the Arctic, the Nature magazine reports.

In 1990, the world pumped 22.7 billion metric tons of carbon dioxide into the atmosphere. By 2010 that amount had increased roughly 45 percent to 33 billion metric tons. Carbon dioxide emissions skyrocketed by more than 5 percent in 2010 alone, marking the fastest growth in more than two decades as the global economy recovered from its slump.

Deterioration was also seen on the biodiversity front.

Governments first agreed back in 1992, at the Rio Earth Summit that the ongoing loss of biodiversity needed attention. The Convention on Biological Diversity (CBD) was born there, aiming to preserve the diversity of life on Earth.

However, Ahmed Djoghlaf, executive secretary of CBD at the time, said in 2010, Let us have the courage to look in the eyes of our children and admit that we have failed.

Djoghlaf lamented that countries were nowhere near to meeting the treaty's chief goal of significantly cutting species loss by 2010. Instead, he said, we continue to lose biodiversity at an unprecedented rate.

Some 30 percent of amphibians, 21 percent of birds and 25 percent of mammal species are at risk of extinction, according to the International Union for Conservation of Nature, based in Gland, Switzerland.

This list can go on and on.

So, can the upcoming Rio+20 really achieve something solid? Supporters are rather confident.

In an exclusive interview with China Daily in New York, Chinese diplomat Sha Zukang, secretary-general for Rio+20 and U.N. undersecretary-general for economic and social affairs, expressed confidence the Brazilian meeting won't be just another U.N. conference but will establish concrete goals.

Rio+20 must be the place where decisions on the future of the planet are made for the next 10 or 20 years. It cannot be another talk shop. World leaders need to adopt an ambitious and yet practical outcome that equals the magnitude of today's challenges, Sha said.