This week people are streaming into Rio de Janeiro for the year's biggest international event the UN Conference on Sustainable Development to be held on Wednesday and Thursday.

It is more popularly known as the Rio+20 Summit, to commemorate the landmark Earth Summit of 1992, which brought the environmental crisis into the mainstream of political life.

Rio+20 is meant to reaffirm the political commitments made then and to come up with new action plans to counter the crises which have become much more serious than 20 years ago. But the developed countries now appear reluctant to make a simple reaffirmation of the original Rio equity principle, or to re-commit to provide finance and technology transfer.

Rio+20 can be a success if it properly addresses some key issues.

The first contested issue is whether the political commitments made in 1992 will be reaffirmed as still valid today. For developing countries, a "must" is the reaffirming of the Rio principles, especially common but differentiated responsibilities.

Under the common but differentiated responsibilities, all countries have the duty to act but developed countries have to do the most in environmental action and must provide finance and technology transfer to developing countries so that they can move toward sustainable development. Failure to endorse this principle would be seen as a big retreat from Rio 92.

The second issue is the green economy, designated as a priority issue for Rio+20. The problem is that there is no internationally agreed definition of this term. Developing countries are concerned that the green economy will replace sustainable development as the key paradigm in the environment-development nexus with the loss of the Rio 92 consensus. They are also worried that the term may be misused as grounds for trade protectionism and aid conditionality.

They want it to be defined as just a tool to achieve sustainable development and not a new policy prescription or framework.

However, developed countries believe the green economy is an important new concept that can lead to changes in the way economies are organized. The Europeans want Rio to endorse a UN green economy roadmap with environmental goals, targets and deadlines. This is facing resistance from many.

The third issue is the sustainable development goals, which are expected to be one of the key "deliverables" at Rio. The developing countries have accepted sustainable development goals as a concept and an operational tool. They want the three pillars (social, economic, environment) to be represented in a balanced way in selecting the goals, and they are concerned that the European Union has put forward only environment goals.

Rio+20 will launch a post-Rio process to decide on the goals and their details, since it is too late to come up with a definitive list. However, most developed countries, especially the EU, want some sustainable development goals (energy, water, oceans, land issues) to be listed as priority goals. However, any list of sustainable development goals must balance the three pillars and there is no agreement yet on how to select the goals.

Another dispute is on who should formulate the sustainable development goals after Rio. Developed countries want the UN Secretary- General and his selected experts to draw up the goals, whereas the G77 wants governments to do it.

A fourth issue is the institutional framework for sustainable development, or how to ensure the institutions are up to the task. There are various proposals, including creating a Sustainable Development Council that meets regularly and a high-level political forum on sustainable development with annual ministerial meetings.

There is also broad agreement that the United Nations Environment Programme has to be strengthened and given more resources. However there is an ongoing dispute as to whether the UNEP should become a UN specialized agency.

Finally a hotly contested issue is providing finance and technology to developing countries to enable their switch to environmentally sound development paths, as was successfully argued 20 years ago.

The developing countries insist that Rio+20 should at least renew the original commitments of new and additional financial resources, and that efforts are made to meet the aid target of 0.7 percent of gross national product. But even these minimal aspects are being resisted by some developed countries, especially the US and Canada.

The developing countries have proposed that developed countries provide at least $30 billion a year until 2018 and $100 billion a year from 2018 onward, and set up a sustainable development fund.

The major developed countries have agreed neither, nor have they vowed to reaffirm the 1992 commitments to provide technology transfer on concessional and preferential terms to developing countries.

Instead they have proposed the term "voluntary transfer of technology on mutually agreed terms". This implies sale of equipment on commercial terms, which is opposed to the technology transfer concept. Even mild language to have a balanced approach to intellectual property rights has been rejected, as has the concept of enhanced access by developing countries to environmentally sound technology.

The above issues will eventually have to be ironed out. Success will require trust to be rebuilt by reaffirming the principles and action framework of Rio 92.

The commitments made on providing finance and technology transfer to developing countries have to be renewed and made relevant to present needs. Action plans for various subjects should be endorsed. A commitment to bring about new or at least stronger institutions has to be made. And agreement has to be reached on the green economy and sustainable development goals, which have consumed a lot of the energy and time in the preparations for Rio+20.

The author is executive director of South Centre, a think tank of developing countries, based in Geneva.