Surprisingly accurate nautical maps created the 17th to 19th centuries strongly suggest coastal land area in both hemispheres were quite similar to today’s. There is even evidence relative sea levels were higher than now back then.
Image Source: Etsy.com
Globally, coasts have grown since the 1980s
Between 1985 and 2015, satellite observations indicate the world’s coasts gained 13,565 km² more land area than they had lost to the seas (Donchyts et al., 2016).
This means more coastal land area is above sea level today than in the 1980s.
This surprises 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)
Duvat (2019) also identified a global trend in island shoreline net growth since the 1980s despite recent sea level rise, as none of the globe’s islands larger than 10 ha – and just 1.2% of the 334 islands larger than 5 ha – have decreased in size since the 1980s.
These recent trends would appear to be the opposite of what would be expected with modern global warming.
Are relative sea levels lower now than during the 1800s?
As the climate warms and glaciers and ice sheets melt, it’s assumed coasts should be much smaller today than they were during the much colder and more glaciated Little Ice Age (1400-1900 A.D.).
But shorelines are not clearly smaller today according to highly detailed maps dated to the 17th to 19th centuries.
Below are 4 examples of direct comparisons between today’s Google Maps images of islands and maps from 1802, 1873, 1893, and even 1640. Each suggest there may have been slightly more land area underwater during the Little Ice Age than today.
1. An 1893 nautical map of the UK’s Isle of Man shows there was more land area underwater in 1893 than in 2019.
Image Source: Antique Maps Online
2. Here is an 1802 nautical map of New York City and Long Island. There may have been more open waters in this region during the Little Ice Age than in 2019.
Image Source: Amazon.com
3. A 1640 Dutch map of Taiwan shows this land area was no larger than it is today during the Little Ice Age. It even seems small nearby islands were further underwater 380 years ago than they are now.
Image Source: Wikipedia
4. An 1873 nautical map of Tasmania shows similar-sized to smaller coastal land area nearly 150 years ago when compared to images from today.