"In my view, climate change and the loss of biodiversity are the most alarming challenges on the global agenda," Gabriel said in a speech opening the conference, held once every two years.

He vowed to do all he could to reach accord, saying countries had to answer inconvenient questions and take action rather than produce "huge amounts of paper with little content".

"It will be a Herculean task to get the world community and each individual country on the right path to sustainability," Gabriel said, noting that extinction rates were 100 to 1,000 times higher than natural rates.

Some 5,000 delegates from nearly 200 countries met in Bonn for a two-week Convention on Biological Diversity conference at which they aim to agree on ways to slow rising extinction rates.

A UN summit in 2002 set a goal of slowing the rate of biodiversity loss by 2010 but experts say that goal is far off.

"The truth today is that we are still on the wrong track. If we follow this path we can foresee that we will fail to meet the target," said Gabriel.

The International Union for Conservation of Nature published a report saying one in eight of the world's birds are at risk of extinction as climate change puts birds under increasing pressure, according to data compiled by BirdLife International.

POLITICAL TOPIC

Biodiversity has jumped up the political agenda due partly to a recent surge in food prices, which has been linked to booming demand in fast-growing economies, including China, and the growing use of crops to provide fuel.

Experts say agricultural crops will suffer if wild stocks die out. Without a change in human consumption habits, feeding 9 billion people would be impossible, they warn.

"The world is watching this conference and we cannot fail," the Convention on Biological Diversity Executive Secretary Ahmed Djoghlaf told a news conference.

"Business as usual is no more an option if humanity is going to survive. Losing biodiversity is not just losing trees and species, it is an economic and security loss."

He and Gabriel pointed to a study which put the annual value of the world's protected areas at $5 trillion, in services such as food, timber or water purification, compared to $1.8 trillion in annual revenues for the automotive industry.

Gabriel told the delegates biodiversity affected the lives of the world's poorest people and if no action was taken, commercial fishing would have to end by 2050 -- a devastating scenario for millions of people who rely on fish protein.

Gabriel said a priority of the conference, which ends on May 30, was to agree on the framework for a 2010 deal on binding rules on access to genetic resources and sharing their benefits.

Developing countries want to ensure they get a share of the financial rewards from their natural resources which pharmaceutical and biotechnology firms are keen to tap.

"This summit is a unprecedented opportunity for governments to stop talking and start acting," said Greenpeace International campaigner, Martin Kaiser.