Rapid Sea Level Rise Was Supposed To Shrink Earth’s Coasts. It Hasn’t

“Over the past decades, atoll islands exhibited no widespread sign of physical destabilization in the face of sea-level rise.

“88.6% of islands were either stable or increased in area, while only 11.4% contracted.

“It is noteworthy that no island larger than 10 ha decreased in size.

These results show that atoll and island areal stability is a global trend, whatever the rate of sea-level rise.”- Duvat, 2019

Image Sources: Donchyts et al., 2016 and BBC (press release)

I. Despite sea level rise, “the coasts are growing all over the world”

Sea levels aren’t rising fast enough to deleteriously affect coastal areas on a net global scale.

Satellite observations indicate there have been 13,565 km2 of net growth in the land area across the globe’s coasts between 1985-2015.

In other words, the Earth’s coasts gained more land area then were lost to rising sea levels.

“Earth’s surface gained 115,000 km2 of water and 173,000 km2 of land over the past 30 years, including 20,135 km2 of water and 33,700 km2 of land in coastal areas.” (Donchyts et al., 2016)

As a visual example, Ahmed et al. (2018) find that Bangladesh’s coastal land area grew by 7.9 km² per year during 1985-2015.

“This paper draws upon the application of GIS and remote sensing techniques to investigate the dynamic nature and management aspects of land in the coastal areas of Bangladesh. … This research reveals that the rate of accretion [coastal land growth] in the study area is slightly higher than the rate of erosion. Overall land dynamics indicate a net gain of 237 km² (7.9 km²annual average) of land in the area for the whole period from 1985 to 2015.”  (Ahmed et al., 2018)

Image Source: Ahmed et al., 2018

II. Even with ~4 mm yr⁻¹ local sea level rise, Pacific islands grew in size during 1971-2014

Between 1958-2014, the globe’s sea levels rose at a rate of about 1.4 mm yr⁻¹ , or 14 centimeters (5.5 inches) per century (Frederikse et al., 2018).

Ice melt from Greenland and Antarctica contributed a grand total of 1.5 cm of the 7.9 cm (3.1 inches) of sea level rise during those 56 years.

“The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr⁻¹ over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr⁻¹ for the sum of contributors.” (Frederikse et al., 2018)

However, there are regions of the world where sea levels are rising at rates two or three times the global average.

Tuvalu, representing over 100 islands located in the central west Pacific, has undergone “twice the global average” rate of sea level rise (~3.90 ± 0.4 mm yr⁻¹) since the 1970s.

It would be expected that such high rates of local sea level change would result in shrinking island coasts and overall land area during this period.

But the opposite has occurred. There has been a net increase in the coastal land area of Tuvalu between 1971-2014 in 8 of 9 atolls.

“We specifically examine spatial differences in island behaviour, of all 101 islands in Tuvalu, over the past four decades (1971–2014), a period in which local sea level has risen at twice the global average. Surprisingly, we show that all islands have changed and that the dominant mode of change has been island expansion, which has increased the land area of the nation.”

“Using remotely sensed data, change is analysed over the past four decades, a period when local sea level has risen at twice the global average (~3.90 ± 0.4 mm yr−1). Results highlight a net increase in land area in Tuvalu of 73.5 ha (2.9%), despite sea-level rise, and land area increase in eight of nine atolls.” (Kench et al., 2018)

III. The stability or coastal net growth of islands in recent decades to century “is a global trend”

Coastal stability and expansion for atoll and island land area is not just a regional trend, but a global one.

A comprehensive (709 islands) review of coastal changes that have been observed in the last decades to this century (Duvat, 2019) reveals that no atoll island destabilization has occurred due to the effects of rising sea levels.

In fact, 88.6% of the globe’s islands have coasts that are either stable or expanding in size.

Further, not a single island larger than 10 hectares [1 ha = 10,000 square m, or 2.5 acres] has decreased in size in recent decades.

None of these observed trends affirm the popularized claim that modern sea level rise is currently threatening the globe’s coasts.

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