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A carbon unicorn perhaps?
Climate scientists meeting in Korea are urged to avoid relying on untested technologies to keep the global temperature rise below 1.5 ° C.
The Intergovernmental Panel on Climate Change will soon publish a report on how the world could stay below this limit.
Early drafts indicated that it would require machines to suck carbon from the air.
The ideas are unrealistic, said an expert, calling them "unicorns of carbon".
The IPCC special report, to be released on Monday, is expected to indicate that the use of technology is an essential element of efforts to stay below the safety threshold.
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Previous versions of the document indicated that all solutions to keep the temperature below 1.5 ° C required a rapid reduction in global greenhouse gas emissions, with net zero being achieved by mid-century.
If emissions continue at the current rate, the world will "exceed" 1.5 ° C by 2040.
What are these technological solutions?
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BECCS: Wood pellets are burned in power plants
If this happens, researchers believe that carbon dioxide removal technologies, in one form or another, would be needed to help bring back the temperature of the Earth.
The IPCC report should mention a number of approaches ranging from planting a larger number of trees to direct CO2 capture in the air, via bioenergy with carbon capture and storage (BECCS).
The latter consists in cultivating large quantities of plants that capture CO2, then burning them to produce energy, while capturing and storing the gas emitted.
This has long been a controversial approach – requiring huge amounts of land to grow crops to burn. Previous research had calculated that an area twice as large as India would be needed to help the world stay below the 2 ° C warming threshold of this century.
"It sounds crazy and it's crazy," said Dr. Glen Peters, a researcher in climatology at the Center for International Climate and Environmental Research in Oslo, Norway.
"But it may be the only way to keep temperatures well below 2 ° C.
"I have a hard time understanding how the world can eliminate billions of tons of carbon from the atmosphere for decades, but if we want 1.5 ° C, we have to accept the fact that it's a good thing. perhaps the only way possible. "
Others agree that BECCS is possible but impractical because it diverts huge amounts of land from food production while the world's population is expected to reach 9 billion people.
Where are the forests?
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Planting trees on a large scale may be necessary to limit global warming
Forty leading forestry researchers signed a letter stating that BECCS was not the "first solution".
"To obtain significant amounts of carbon dioxide by using wood as a source of energy and capturing the resulting carbon in geological reservoirs requires technology that has not yet been tested on a large scale" , write the authors.
They believe that the protection and sustainable management of the forests we already have, as well as the restoration of the ones we have lost, are the best use of trees to limit climate change.
"The future climate of our planet is inextricably linked to the future of its forests," they say.
Why not just suck CO2 from the air?
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ENGINEERING CARBON
Some propose to filter the air to eliminate greenhouse gases
The IPCC report will also mention the use of machines that capture CO2 directly in the air. A number of companies around the world have developed this type of technology, with some success.
Earlier this year, the Canadian company Carbon Engineering released a peer-reviewed research paper showing that CO2 can be captured in the air for less than $ 100 per tonne. The company has now raised more than $ 11 million to expand its existing pilot project and design its first commercial plant.
But some environmentalists see a great danger in all these negative emissions ideas. They believe that these are mythical solutions that allow people to continue using coal, oil and gas.
"Some countries whose economies are based on fossil fuels are not yet ready to face the reality and will want to continue digging and selling these fossil fuels for a while," an expert climate scientist told BBC News.
"I suppose they assume that in the future, unicorns will appear and suck up the surplus carbon from the atmosphere!"
Another factor that may complicate the rapid reduction in the use of fossil fuels is the continued growth of coal as a source of energy.
A new analysis by a group of environmental organizations indicates that 1,380 new coal units or plants are planned or under development in 59 countries. If constructed, these plants would add 672,124 megawatts of capacity to the global coal-fired power plant, an increase of 33%.
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The IPCC special report on a temperature rise of 1.5 ° C is called SR15
