Microsoft and other firms attending the Rio+20 business forum are falling over each other to prove their corporate responsibility credentials, but critics remain highly skeptical about their commitments.

About 1,000 business chiefs from around the world are attending a four-day Corporate Sustainability Forum, organized by the Global Compact.

The Compact, a UN initiative to encourage businesses worldwide to respect human rights, labor, environment and anti-corruption principles, has 7,000 corporate participants in 135 countries.

Scores have already responded to a call to do the right thing and commit to actions and partnerships that advance progress along the forum's six core themes.

These are energy and climate, water and ecosystems, agriculture and food, social development, urbanization and cities, economy and financing.

Sunday, US technology titan Microsoft announced plans to achieve net zero emissions for its data centers, sofware development centers, software development labs, offices and employee air travel by boosting energy efficiency and buying renewable energy.

"We said we would be carbon neutral starting July 1," Rob Bernard, Microsoft's chief environmentalist strategist, told a press conference.

This would be achieved in part through offset, meaning balancing a measured amount of carbon released with an equivalent amount sequestered, or buying enough carbon credits to make up the difference.

Luxembour-based ArcelorMittal, the world's largest steelmaker, says it will reduce its CO2 emissions by 8 percent for every ton of steel produced by 2020, based on a 2007 baseline.

In Brazil, Netafim, a global leader in smart drip and micro-irrigation solutions says it is working with the ministry of integration to install 1000 family drip systems on small-scale farms in the northeastern state of Piaui by 2014.

Drip irrigation helps save water and fertilizer by allowing water to drip slowly to the roots of plants, either onto the soil surface or directly onto the root zone.

US chemicals giant Dupont is committing $10 billion by 2020 to research and development and plans to launch 4,000 new products by the end of 2020 to produce more food, enhance nutrition and food and farming sustainability worldwide.

South Africa's state-owned utility Eskom and US Duke Energy have pledged to assist the development of an electrification roadmap to ensure 500 million people across Africa and developing countries have access to energy by 2025.

These are some of the more than 100 corporate commitments which organizers say will be announced at the close of the forum Monday along with recommendations for Rio+20 summit leaders due to meet here from Wednesday to Friday.

But critics have accused the Global Compact of acting as a marketing tool for big business.

The Compact rejects the charge, saying its scheme incorporates a strict accountability mechanism under which signatories must report annually on their implementation or risk expulsion.

On the commitments made by Eskom and Duke Energy, Daniel Mittler, political director of Greenpeace International, told AFP: "(They) are trying to look good here at Rio, but they are amongst the worst polluters and are actively holding back sustainable development."

Greenpeace is also taking Microsoft, one of three largest owners of data centers in the world along with Amazon and Apple, to task for not quitting the coal habit.

"Giant data centers which store and send the terabytes of pictures, emails, songs and streaming videos we enjoy every day are now one of the fastest growing sources of new electricity demand in the world," the group said. "Every day, tons of asthma-inducing, climate destroying coal pollution is thrown in the air to keep the Internet humming."

"Rio+20 will be known as Greenwash+20 because governments are failing to hold corporations to account and are serving the interest of polluters not their people," said Mittler.