Thursday, October 26, 2017

Sea-Level Rise

Coastal cities around the world could be devastated by 1.3m of sea level rise this century unless coal-generated electricity is virtually eliminated by 2050, according to a new paper by Alexander Nauels from the University of Melbourne.


In 2016, Robert DeConto from the University of Massachusetts Amherst revealed that Antarctica could contribute to massive sea level rise much earlier than thought, suggesting ice sheet collapse would occur sooner and identifying a new process where huge ice cliffs would disintegrate. But that paper only examined the impact of Antarctica on sea level rise, ignoring other contributions, and didn’t examine the details of what measures society needed to take to avoid those impacts. According to the new paper that combines the latest understanding of Antarctica’s contribution to sea level rise and the latest emissions projection scenarios it confirms again that significant sea level rise is inevitable and requires rapid adaptation.
John Church, a leading sea level rise expert from the University of New South Wales who was co-convening lead author of the chapter on sea level in the third and fifth IPCC Assessment Reports, told the Guardian the work was further confirmation that the world needed to prepare now for substantial sea level rises. “Under all scenarios we are going to have to adapt,” Church said. “We cannot stop all sea level rise.”
 Using simplified physical models that allowed them to explore all known contributions to sea level rise, and pair them with the new generation of emissions scenarios which the Intergovernmental Panel on Climate Change (IPCC) will use in the next set of reports. They found that if nothing is done to limit carbon pollution, then global sea levels will rise by an estimated 1.32m. That is 50% more than was previously thought, with the IPCC’s AR5 report suggesting 85cm was possible by the end of the century.
But the extra contribution from Antarctica would not kick in if warming was kept at less than 1.9C above preindustrial levels, the researchers found. Temperatures above that threshold risked triggering the additional processes in Antarctica identified in the 2016 paper, causing much greater sea level rise. The work, published in the journal Environmental Research Letters, showed that the current carbon reduction pledges which governments have made as part of the Paris Agreement by 2030 – their Nationally Determined Contributions (NDCs) – are so weak they would require very deep cuts between 2030 and 2050 to avoid triggering those extra processes in Antarctica.
The authors used the next generation of emissions scenarios (the “Shared Socioeconomic Pathways”), which include assumptions about socioeconomic factors that are driving emissions – such as energy demand, energy generation, population growth and GDP – they were able to examine what actions could be taken to avoid the sea level rise.
 If coal could only make up 5% of the world’s energy mix by 2050 if sea level rise is to be limited to about half a metre.
Similarly, a global carbon price would have to be well over US$100 per tonne, since at that cost, sea level would rise by 65cm by 2100.

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