Sea level rise projections increasing

(Hat tip to Zeke Hausfather)


The new National Climate Assessment from the Trump administration shows more severe high-end sea level rise scenarios than were featured in the last IPCC report: up to 8 feet (2.4 meters) by 2100:

Since 1900, global average sea level has risen by about 7–8 inches (about 16–21 cm). The rate of sea level rise over the 20th century was higher than in any other century in at least the last 2,800 years, according to proxy data such as salt marsh sediments and fossil corals. Since the early 1990s, the rate of global average sea level rise has increased due to increased melting of land-based ice.  As a result, almost half (about 0.12 inches [3 mm] per year) of the observed rise of 7–8 inches (16–21 cm) has occurred since 1993.

Over the first half of this century, the future scenario the world follows has little effect on projected sea level rise due to the inertia in the climate system. However, the magnitude of human-caused emissions this century significantly affects projections for the second half of the century and beyond. Relative to the year 2000, global average sea level is very likely to rise by 0.3–0.6 feet (9–18 cm) by 2030, 0.5–1.2 feet (15–38 cm) by 2050, and 1–4 feet (30–130 cm) by 2100. These estimates are generally consistent with the assumption—possibly flawed—that the relationship between global temperature and global average sea level in the coming century will be similar to that observed over the last two millennia. These ranges do not, however, capture the full range of physically plausible global average sea level rise over the 21st century. Several avenues of research, including emerging science on physical feedbacks in the Antarctic ice sheet (e.g., DeConto and Pollard 2016, Kopp et al. 2017) suggest that global average sea level rise exceeding 8 feet (2.5 m) by 2100 is physically plausible, although its probability cannot currently be assessed (see Sweet et al. 2017, Kopp et al. 2017).

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Note how each successive estimate of the likely rise in sea level has been higher than the previous one, and how the range has increased.  It's tempting to hope that the actual rise is at the low end of the projections.  But why should it be that way?  It could just as easily be at the high end of projections.  Consider what will happen to Miami if sea level rise by 2100 is actually 2.4 metres, more than the height of even the tallest man.