Agriculture is part of the solution to the world's environmental challenge and must play a key role at next June's Rio summit on sustainable development, the Brazilian head of the UN food agency said here Tuesday.

"Agriculture ministers from the entire world must be present at the Rio+20 meeting (in June) so that agriculture commits itself to helping clean up the planet," Jose Graziano da Silva, the new boss of the Food and Agriculture Organization (FAO), said.

"Agriculture contributes 30 percent of the greenhouse gases that cause global warming and we must raise the awareness of our farmers," he added during an event organized by local authorities ahead of the opening of the World Social Forum (WSF) here later Tuesday.

The Rio+20 summit next June, the fourth major summit on sustainable development since 1972, will call on world leaders to commit themselves to creating a social and "green economy," with priority being given to eradicating hunger.

The WSF, which runs through Sunday, brings together tens of thousands of anti-capitalist militants opposed to the World Economic Forum, the annual gathering of the world's economic and political elites being held at the same time in the Swiss resort of Davos.

Forum participants are to mull alternative solutions to the global economic crisis and prepare the ground for a peoples' summit of social movements to be held in parallel to next June's Rio+20 summit on sustainable development.

"Agriculture is not just part of the problem, it is also part of the solution to the environment issue. It can contribute a lot to the planet's sustainable development, by finding techniques less harmful to the environment, by helping with clean energy and with a better redistribution of production," Graziano said.

Graziano is a former Brazilian food security minister and the first Latin American to head FAO, a UN agency which battles hunger affecting over a billion people globally.

He is internationally acclaimed for his role in designing and implementing Brazil's "Zero Hunger" ("Fome Zero") program, which helped lift 24 million people out of extreme poverty.

In his address, the 61-year-old professor, who was elected last June and took up his post early this month, pledged to open FAO doors to civil society.

"FAO must open its doors to society. We are trying to create space for dialogue with society to break the monopoly of dialogue with governments, with some specific governments, as occurred over the past few years," Graziano noted.

Stressing that social movements were seeking reality, not utopia, he added: "Utopia is to think that solution exists on the margins of society, that there can be sustainable development without food security, that we can live in peace with nearly one billion of starving people in the world."

He criticized what he called the "roulette" of world commodities prices.

He said farm production would need to grow five times bigger and pointed out that 90 percent of this increase could be achieved with better productivity and not at the expense of the environment.

And Graziano urged Brazil, now the world's sixth largest economy, to "assume its international responsibility" in the fight against world hunger "with a new form of international cooperation" that respects developing countries.