Chapter 4: Sea Level Rise and Implications for Low Lying Islands, Coasts and Communities

OPPENHEIMER M; GLAVOVIC B; HINKEL J....; ISLA F

SROCC report AR6

IPCC

Lugar: New York; Año: 2019; p. 1 - 169

Executive Summary This chapter assesses past and future contributions to global, regional and extreme sea level changes, associated risk to low-lying islands, coasts, cities, and settlements, and response options and pathways to resilience and sustainable development along the coast. Global mean sea level (GMSL) is rising (virtually certain 1 ) and accelerating (high confidence 2 ). The sum of glacier and ice sheet contributions is now the dominant source of GMSL rise (very high confidence). GMSL from tide gauges and altimetry observations increased from 1.4 mm yr ?1 over the period 1901?1990 to 2.1 mm yr ?1 over the period 1970-2015 to 3.2 mm yr ?1 over the period 1993?2015 to 3.6 mm yr ?1 over the period 2005?2015 (high confidence). The dominant cause of global mean sea level rise since 1970 is anthropogenic forcing (high confidence) (4.2.2.1.6, 4.2.2.5). Global mean sea level was considerably higher than today during past climate states that were slightly warmer than preindustrial, including the Last Interglacial (LIG; 129?116 thousand years ago), when global mean surface temperature was 0.5ºC to 1.0ºC warmer, and the mid-Pliocene Warm Period (mPWP; ~3.3 to 3.0 million years ago), 2º-4º C warmer. Despite the modest global warmth of the Last Interglacial, Greenland and Antarctic ice sheets contributed 6-9 m to GMSL (high confidence), but not more than 10 m (medium confidence). Based on new understanding about geological constraints since AR5, 25 m is a plausible upper bound on GMSL during the mid-Pliocene Warm Period (low confidence). Ongoing uncertainties in paleo sea-level reconstructions and modeling hamper conclusions regarding the total magnitudes and rates of past sea level rise. Furthermore, the long (multi-millennial) timescales of these past climate and sea level changes, and regional climate influences from changes in Earth?s orbital configuration and climate system feedbacks, lead to low confidence in direct comparisons with near-term future changes. (4.2.2, 4.2.2.1, 4.2.2.5, CCB-5, Supplementary Material (SM) 4.1)