The difference between the Paris climate agreement's two alternative temperature targets – 1.5°C (2.7°F) and 2.0°C (3.6°F) above pre-industrial levels – may be the difference between life and death for some coastal ecosystems threatened by sea-level rise.
That is a key finding of new research from Tufts University, Rutgers University–New Brunswick, and the Potsdam Institute for Climate Impact Research, published today in the journal Environmental Research Letters.
"Although the 2015 Paris Climate Agreement aims to hold global average temperature to 'well below 2°C above pre-industrial levels, and pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels', projections of global average sea-level rise usually focus on scenarios with a high probability of warming exceeding 1.5°C," said lead author Dr Klaus Bittermann, from Tufts University.
The researchers used statistical modelling to project sea-level changes between now and 2150, under a variety of temperature scenarios that satisfy one of the two Paris Agreement temperature targets.
The team found that stabilising the temperature at 1.5°C instead of 2°C would reduce global average sea-level in 2150 by about 7 inches (17 cm), and reduce peak rates of rise by about 0.7 inches per decade (1.9 mm per year) – more than the average rate of rise over the last century.
Their results showed that delaying the year of peak temperature had little long-term influence on GMSL, but did reduce the maximum rate of sea-level rise significantly.
Dr Bittermann said: "Even among futures that satisfy the 1.5°C or 2°C targets set out in the Paris accord – both of which require very quick reductions of greenhouse gas emissions – there is still significant variation in how sea level responses.
"Although both temperature targets reduce the amount and the rate of sea level rise significantly compared to a future in which we continue to burn fossil fuels, faster reductions in fossil fuels can significantly reduce the peak rate of rise."
Co-author Professor Andrew Kemp, from Tufts University said: "The difference in peak rates of sea-level rise between the scenarios is large enough that it could represent the difference between drowning and survival for some vulnerable ecosystems."
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Klaus Bittermann et al. Global mean sea-level rise in a world agreed upon in Paris, Environmental Research Letters (2017). DOI: 10.1088/1748-9326/aa9def