An urgent appeal to everyone in the Iraq war to think again has been launched by 38 leading scientists.
By Alex Kirby
BBC News Online environment correspondent
They are members of the council of IUCN-The World Conservation Union, representing 70 governments.
A statement by the Swiss-based IUCN urges all involved "to stand back" and see the wider picture.
It says war "is always a tragic failure", leaving immense costs in its wake.
IUCN says: "We find ourselves confronted with events whose impact could undermine sustainability long into the future.
"IUCN has followed with increasing concern the armed conflict in Iraq," the statement says, and it wants to contribute to "averting the humanitarian and environmental tragedy that inevitably follows from war".
The scientists say Protocol 1 of the Geneva Conventions bans the use of methods of warfare intended or expected to cause widespread, long-term and severe damage to the natural environment.
The statement says IUCN concluded the environmental consequences of the 1991 war against Iraq had caused widespread, devastating damage extending far beyond the conflict itself.
Iraq has drained the Mesopotamian marshes
"A repetition of the damage caused then to rivers, wetlands, marshes, the desert and the seas will have disastrous long-term impacts.
"Damage to the natural environment from armed conflict can undermine the natural resource base on which millions of people depend for their livelihood.
"Armed conflict is always a tragic failure. Although in some extreme circumstances it takes force to move through to a new stage of cooperation and progress, the human and ecological price that is paid for modern warfare is colossal, and the debt it leaves behind takes years or decades to pay off.
"While it is difficult in the current atmosphere of crisis to stand back and put the situation in its broader perspective, that is nevertheless what we must do...
"A sustainable future requires a robust economy, social equity and justice, and sound management of the Earth's resources. None of these intimately-related goals can be advanced in time of armed conflict."
Dr Jeff McNeely, IUCN's chief scientist, told BBC News Online: "The environment paid a very high price for Saddam Hussein's expulsion from Kuwait.
"The environmental price to be paid this time may be much heavier than in 1991.
"Conflict is a human tragedy. The combatants need more time - to think.
"A lot of conflict in the region is over resources - not just oil, but especially water. We may be able to help by advising on resource management."
He said IUCN was especially worried about biological weapons. "They could be devastating to both people and animals.
The US' 21,000lb massive ordnance air blast bomb - Moab
"In the Iran-Iraq war rinderpest became a real epidemic in both countries. Nobody knows if it was used as a weapon.
"There's a fungus called Fusarium which attacks palm trees. It first appeared in the area in 1991 - it had been unknown there before.
"Biological weapons have been called 'the poor man's nuclear bomb', and using them in war simply demonstrates how effective they are."
The 38-member council is IUCN's principal governing body between sessions of the World Conservation Congress, the general assembly of its members, who include about 750 non-government organisations.