By Richard Black
Environment correspondent, BBC News website, Barcelona
The congress takes place as environment indicators worsen
Businesses must change their attitude to environmental issues if the tide of ecological decline is to be halted.
That was the message from Valli Moosa, president of the International Union for the Conservation of Nature, opening the World Conservation Congress.
The former South African minister said all companies should have directors with environmental experience.
The 10-day IUCN congress in Barcelona will debate global environmental problems and potential solutions.
The organisation numbers almost all the world's governments, environment groups and business representatives among its members.
Mr Moosa spoke frankly about his view that unfettered markets and businesses are largely responsible for the world's current environmental ills.
"Leading entrepreneurs and markets have certainly contributed to the growth of the global economy; yet while individuals may be moral, markets are not," he told delegates.
"The damage industries and commerce do to people and the environment is real, it is considerable, and it is unacceptable."
But, he added, it was also unnecessary.
Concerns over climate change are now widespread
Businesses had a short-term interest in saving money through saving energy, and every boss had a different kind of interest in leaving the world an environmentally sound place for their children.
Every business, he said, should include at least one non-executive director with a working knowledge of environmental issues, just as they should include someone with a working knowledge of accountancy.
But while business practices must change, said Mr Moosa, governments too had a key role in bringing about change if our global society was to switch to a more sustainable path.
One vital task was to reach a binding deal on constraining greenhouse gas emissions, he said - a task that looks more difficult now that eastern European countries are challenging EU moves to cut emissions and deploy renewable energy, and with a report out last week suggesting that emissions globally are rising faster than ever.
The congress, which marks IUCN's 60th anniversary, takes place against the backdrop of increasing evidence that almost all global environmental indicators point downwards.
This was the picture starkly painted by the United Nations Environment Programme (Unep) last year in its five-yearly Global Environmental Outlook.
The report concluded that the current high rate of species loss, climate change, deforestation, overfishing, desertification and pollution, coupled with population growth, meant that future generations would inhabit a less healthy planet.
Tamas Marghescu, IUCN's director for Europe, agreed with the diagnosis.
"The potential area for nature and biodiversity is disappearing, the foundation of our sustainable life is disappearing," he told BBC News.
"So my conclusion is that the world is not going in a sustainable direction, and we need a new paradigm of sustainability."
He suggested that part of the solution could lie in adequately valuing the services that natural resources perform for humanity, such as processing out waste, regulating the Earth's temperature and providing fresh water.
Just as the Stern Review outlined the economic costs of not mitigating climate change, a major exercise under the aegis of the European Commission is attempting to quantify the costs of not stemming the loss of species, estimated to be running at between 100 and 1,000 times the natural rate.
Mr Moosa suggested that the number of people and institutions sceptical of humanity's role in environmental decline was shrinking.
Within the last two years, he related, the World Economic Forum had signalled its concern on climate change, and the US Pentagon warned that consequences of global warming would include the spread of disease, harsher storms and environmental refugees.
"It seems as though the former sceptics are mainstreaming what we have always known," he said.