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Friday, November 21, 2014

Drop Dead Date

The UN has released the “drop dead” date for CO₂ emissions to be zeroed: 2070. CO2 emissions must be zero by 2070 to prevent climate disaster, UN says in The Guardian:
‘Negative emissions’ are needed globally by second half of century to stave off dangerous climate change, say UN scientists.
The world must cut CO₂ emissions to zero by 2070 at the latest to keep global warming below dangerous levels and prevent a global catastrophe, the UN warns.
By 2100, all greenhouse gas emissions — including methane, nitrous oxide and ozone, as well as CO₂ — must fall to zero, the United Nationals Environment Programme (Unep) report says, or the world will face what Intergovernmental Panel on Climate Change scientists have described as "severe, widespread and irreversible" effects from climate change.
The Unep report published on Wednesday is based on the idea that the planet has a finite ‘carbon budget.’ Since emissions surged in the late 19th century, some 1,900 Gigatonnes (Gt) of CO₂ and 1,000 Gt of other greenhouse gases have already been emitted, leaving less than 1,000 Gt of CO₂ left to emit before locking the planet in to dangerous temperature rises of more than 2°C above pre-industrial levels.
Jacqueline McGlade, Unep's chief scientist, told the Guardian that scientific uncertainties about the remaining carbon budget had diminished and the real uncertainty now was whether politicians had the will to act. "The big uncertainty is whether you can put enough policies in place from 2020-2030 — in the critical window — to allow the least-cost pathways [to lower emissions and temperatures] to still stand a chance of being followed," she said. "The uncertainties have shifted from the science to the politics."
All scenarios in the Unep report now require some degree of ‘negative CO₂ emissions’ in the second half of the century, through technologies such as carbon capture and storage or, possibly, controversial, planetary wide engineering of the climate known as geoengineering. Unep is "extremely interested" in the subject and is planning a report in the months ahead.