New Study Finds 12 Of 15 Islands In Florida Bay Have GROWN In Size Since 1953, Continuing A Global Trend

Instead of inundation from sea level rise, 80% of assessed Florida Bay (USA) islands grew in area during 1953-2014, prototyping a global-scale trend in island resistance to rising seas.

Image Source: Zhai et al., 2019

Back in 1989, the United Nations issued a dire warning: either reverse the ongoing global warming by the year 2000, or “entire nations could be wiped off the face of the Earth by rising sea levels” and “coastal regions will be inundated“.

The U.N. specifically referenced Bangladesh’s looming fate, forecasting coastal flooding will dispace 23 million Bangladeshi people.

Now, forty years later, we can assess the effect global warming has had on Bangladesh.

From 1985 to 2015, not only did the coastal regions avoid inundation from rising sea levels, Bangladesh’s coastal land area grew at a pace of 7.9 km² per year during this span!

Image Source(s): AP News (1989) and Ahmed et al., (2018)

The trend in stable or growing coastal land area amid rising seas has not just been limited to Bangladesh. Indeed, the overall expansion of coastlines for both islands and mainlands has been global in scope.

Between 1985 and 2015, for example, satellite observations indicated the world’s coasts gained 13,565 km²  more land area than they had lost to the seas. This surprised scientists, as they “expected the coast would start to retreat due to sea level rise,” but instead they observed “coasts are growing all over the world.”

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

An analysis of 709 islands from across the globe revealed that no island larger than 10 ha (~25 acres) – which includes the “vulnerable” Maldives, Tuvalu, Fiji, etc. – has decreased in size since the 1980s. In fact, 89% of islands assessed are stable or growing.

Image Source: Duvat et al., 2019

A new paper assessing the area of 15 Florida Bay islands between 1953 and 2014 finds 12 of the 15 grew in size during this timespan, which is consistent with the global trend.

The authors are keen to point out that much of this expansion can be attributed to heavy mangrove forest growth. They apparently don’t view mangrove expansion as a positive development (an “unhelpful resiliance”) due to the tendencies for mangroves to crowd out non-mangrove habitats.

Regardless, Zhai et al. (2019) adds to the growing body of evidence indicating rising seas haven’t been the inundation disaster threat they’ve been made out to be for the last 40 years.

Zhai et al., 2019

Remote sensing of unhelpful resilience to sea level rise caused by
mangrove expansion: A case study of islands in Florida Bay, USA

“To estimate the resilience influences on 15 islands in Florida Bay (Florida, U.S.), our study used indicators (areas of the 15 islands and their mangrove forests) by analyzing 61-yr high-resolution historical aerial photographs and a 27-yr time-series of Landsat images.”

“Comparative spatial analysis of the historical aerial images showed that the island area significantly increased from 1953 to 2014. For example, Joe Kemp Key had the largest area increase from 0.34 km2 to 0.37 km2. Moreover, the similar increased patterns of island area were found for annual total areas of the 15 islands from 1984 to 2011 by analysis of Landsat images. The total areas showed a significant increasing pattern with time. Therefore, results from the analysis of both aerial and satellite images revealed increases in island area, which indicate the island resilience to inundation caused by SLR. However, three islands […] decreased in area.”

“The long-term island area increases estimated by our analysis supported the resilience of Florida Bay islands to SLR inundation. Moreover, both the positive relationship between the increases of island area and mangrove expansion, and previous field studies in the Florida Bay and nearby Caribbean mangroves suggested the contribution of the mangrove expansion were at the expense of non-mangrove habitats.”

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