Differential climate impacts for policy-relevant limits to global warming: the case of 1.5 _C and 2 _C (25 page pdf,Carl-Friedrich Schleussner, Tabea K. Lissner, Erich M. Fischer, Jan Wohland, Mahé Perrette, Antonius Golly, Joeri Rogelj, Katelin Childers, Jacob Schewe, Katja Frieler, Matthias Mengel, William Hare, and Michiel Schaeffer, Earth System Dynamics, Apr. 21, 2016)
Also discussed here: 1.5°C vs 2°C: Why half a degree matters (Newsletter, International Institute for Applied Systems Analysis, Apr. 21, 2016)
Today we review research using scenarios with global climate models that show the difference in impacts from limiting global warming to 1.5 deg C or to 2.0 deg C by taking action to reduce carbon emissions and how quickly this is done. Many authoritative sources from COP 21 in Paris indicated that unless cuts of the order of 50% are taken within a decade (2025) that the 1.5 deg goal will be breached and unless the cuts reach 100% by 2050 that the 2 deg goal is probably unachievable. The paper examines the consequences of taking action too slowly or to a less than acceptable degree.
The impacts affect the length of heat waves (lasting 2 months more for 1.5C or 3 months for 2C), water availability, sea level rise, coral reefs and reduced crop yields. Perhaps the largest impact, sea level rise, has the largest implications because the processes involved in melting ice sheets are so large and slow moving. Once the Greenland ice sheet begins to breakdown, sea level rises of 5-7 m are inevitable over centuries with warming over 2C and will accelerate beyond 2100, while early action to limit warming to 1.5C would limit the sea level rise to 40 cm. Clearly policy makers at both the international and national/subnational levels need to step up to the challenge and soon.
“At the Paris Climate Summit the world decided to try to limit warming to below 1.5°C, in part because many considered climate impacts at 2°C to be too risky. Our new study provides essential new information about the risks under these two warming levels, and will feed into the ongoing international climate talks, helping policymakers deciding on the priority and urgency of climate action,”
“The additional 0.5°C would mean a 10-cm-higher global sea-level rise by 2100, longer heat waves, and greater risk of killing off tropical coral reefs.”
“On a global scale, the researchers anticipate sea level to rise about 50 cm by 2100 in a 2°C warmer world, 10 cm more than for 1.5°C warming. More importantly, however, is the rate at which sea level continues to rise in 2100. In a 1.5°C warmer world, this rate is about 30% lower than in a 2°C world, reducing our commitment to long-term sea-level rise. “
“Substantial increases of 3 _C and more in TXx [hot extremes] over large parts of the Northern Hemisphere, central South America and South Africa as well as increases in warm-spell durations (WSDI) of 3 months and more are projected under a warming of 2 _C…The regional assessments indicate that the tropical regions in Africa, South America and South-East Asia are projected to experience the strongest increase in land area covered by heat extremes relative to the regional natural variability,”
“For a warming of 2 _C, reductions in water availability of up to 30% are projected in several – mainly subtropical – regions, in particular affecting the Mediterranean, South Africa, Central and southern South America and South Australia”