The United Nations should impose a moratorium on "geo-engineering" projects such as artificial volcanoes and vast cloud-seeding schemes to fight climate change, green groups say, fearing they could harm nature and mankind.
The risks were too great because the impacts of manipulating nature on a vast scale were not fully known, the groups said at a major U.N. meeting in Japan aimed at combatting increasing losses of plant and animal species.
Envoys from nearly 200 countries are gathered in Nagoya, Japan, to agree targets to fight the destruction of forests, rivers and coral reefs that provide resources and services central to livelihoods and economies.
A major cause for the rapid losses in nature is climate change, the United Nations says, raising the urgency for the world to do whatever it can to curb global warming and prevent extreme droughts, floods and rising sea levels.
Some countries regard geo-engineering projects costing billions of dollars as a way to control climate change by cutting the amount of sunlight hitting the earth or soaking up excess greenhouse gas emissions, particularly carbon dioxide.
"It's absolutely inappropriate for a handful of governments in industrialised countries to make a decision to try geo-engineering without the approval of all the world's support," Pat Mooney, from Canada-headquartered advocacy organisation ETC Group, told Reuters on the sidelines of the Oct. 18-29 meeting.
"They shouldn't proceed with real-life, in-the-environment experimentation or the deployment of any geo-engineering until there is a consensus in the United Nations that this is okay."
Some conservation groups say geo-engineering is a way for some governments and companies to get out of taking steps to slash planet-warming emissions.
The U.N. climate panel says a review of geo-engineering will be part of its next major report in 2013.
Some of the geo-engineering schemes proposed include:
-- Ocean fertilisation. Large areas are sprinkled with iron or other nutrients to artificially spur growth of phytoplankton, which soak up carbon dioxide. But this could trigger harmful algal blooms, soak up nutrients and kill fish and other animals.
-- Spray seawater into the atmosphere to increase the reflectivity and condensation of clouds so they bounce more sunlight back into space.
-- Placing trillions of tiny solar reflectors out in space to cut the amount of sunlight reaching the Earth.
-- Artificial volcanoes. Tiny sulphate particles or other materials are released into the stratosphere to reflect sunlight, simulating the effect of a major volcanic eruption.
-- Carbon capture and storage. Supported by a number of governments and involves capturing CO2 from power stations, refineries and natural gas wells and pumping it deep underground.
Mooney said the U.N. Convention on Biological Diversity (CBD) should expand its de-facto moratorium on ocean fertilisation agreed in 2008 to all geo-engineering, although the proposal was resisted by some countries, including Canada, earlier this year.
Canada said in Nagoya that it would work with the CBD.
"Canada was simply concerned about the lack of clarity on definitions including what activities are included in 'geo-engineering'," Cynthia Wright, head of the delegation, said in an email response.
"Canada shares concerns of the international community about potential negative impacts of geo-engineering on biodiversity and is willing to work with other CBD Parties to avoid these impacts," she said.
Environmentalists said geo-engineering went against the spirit of the Nagoya talks, which aims to set new targets for 2020 to protect nature, such as setting up more land and marine protected areas, cutting pollution and managing fishing.
"We are certainly in favour of more (geo-engineering) research, as in all fields, but not any implementation for the time being because it's too dangerous. We don't know what the effects can be," said Francois Simard of conservation group IUCN.
"Improving nature conservation is what we should do in order to fight climate change, not trying to change nature."