Leading climate scientists have warned that the Earth is perilously close to breaking through a 1.5oC upper limit for global warming, only eight months after the target was set.
The decision to try to limit warming to 1.5oC, measured in relation to pre-industrial temperatures, was the headline outcome of the Paris climate negotiations last December. However, figures show that average global temperatures were already more than above pre-industrial levels in the past one year.
Atmospheric heating has been partly triggered by a major El Niño event in the Pacific, with 2016 expected to be the hottest year on record. Temperatures above 50C have afflicted Iraq; India is experiencing one of the most intense monsoons on record; and drought-stricken California has been ravaged by wildfires.
The Paris agreement goal to achieve its 1.5C target indicates that countries should reach zero by the second half of the 21st century, a goal that was accepted as being ambitious but possible – until global temperatures increased dramatically this year.
Many scientists now believe the most realistic strategy is to overshoot the 1.5C target by as little as possible and then, once carbon emissions have been brought to zero, carbon dioxide could be extracted from the atmosphere to start to cool the planet back down to the 1.5C target. In other words, humanity will have to move from merely curtailing emissions to actively extracting carbon dioxide from the air, a process known as negative emissions.
Several techniques have been proposed. One includes spreading crushed silicate rocks, which absorb carbon dioxide, over vast tracts of land. Another involves seeding oceans with iron to increase their uptake of carbon dioxide. Most are considered unworkable at present – with the exception of bioenergy with carbon capture and storage. Under this scheme, vast plantations of trees and bushes would be created, their wood burned for energy while the carbon dioxide emitted was liquefied and stored underground.