From time to time, a new marker is placed. Since 2011, the Middle Passage Ceremonies and Port Markers Project has laid down markers and organized ceremonies in honor of the approximately two million enslaved Africans who perished at sea during the period of the transatlantic slave trade between the sixteenth and nineteenth centuries. In the United States alone, the project has identified 52 ports that were at one point directly involved in the trade. Presently, the group managed to place markers in 20 ports, and organize ceremonies in 22. Each marker is unique and the ceremonies incorporate rituals from different religions intended to address the painful memory and legacies of the slave trade. The markers in particular have the additional purpose of reminding future generations about the history of the traffic. However, in this current age of global warming, and rising sea levels, one may very well wonder: how long until these ports are fully submerged?
Data from a couple of digital resources available to the public may help us address this question. The Gradient Fingerprint Mapping tool of NASA’s Jet Propulsion Laboratory at the California Institute of Technology allows users to simulate local sea level changes overtime caused by the melting of glaciers and ice sheets for a total of 187 locations around the globe. Not all of these places participated in the transatlantic slave trade, of course, but many of them did or are located near ports that did so in Africa, Europe, and the Americas. Users can measure local sea level changes by millimeters per year. They can also view projections calculated for 10, 50, 100, 200, and 1000-year periods. Changes in sea level vary according to the Earth’s gravitational and rotational potentials. Meanwhile, patterns of inundation depend on the location of the drainage system. Ice melted from western Greenland, for example, affects London more than New York. The simulation tool unfortunately lacks data on the elevation of the listed places, but the Falling Rain gazetteer provides comparable information in feet and meters for almost every location of the world. A simple conversion is all that is necessary to calculate how long it will take for each place available in the tool to be completely underwater.
The idea that temperatures around the world have been increasing as a function of human activity has gained significant traction lately. However, scholars debate the origins of this relationship. Some date it to the arrival of Europeans to the Americas in the late fifteenth century. Others favor a more recent date, coinciding with the Industrial Revolution in Britain. Be that as it may, the impact has been huge, resulting in a new chapter or epoch in the geological record, recently dubbed the “Anthropocene.” The transatlantic slave trade played a central role in that process of global warming. It involved the transportation of some 12.5 million enslaved Africans on ships departed from Europe and the Americas over a period of almost four centuries. It spread contagious diseases that contributed to the near annihilation of indigenous populations in the Americas. It destroyed forests, cleared lands, opened mines, changed the course of rivers, and built entire new cities where previously none existed. It created new financial institutions that underpinned the traffic and fostered industrialization in Europe and North America, where many of the crops enslaved Africans produced were processed for sale and consumption throughout the world, including sugar, rice, tobacco, and cotton. The slave trade thus contributed not only to global inequality, but to increased temperatures worldwide as well.
In any case, the sea will claim ports north and south of the Equator. To some of them the threat of inundation is imminent. Although sitting somewhat up the Mississippi River, New Orleans is already below sea level and prone to floodings caused by tropical storms, another hazard intensified by global warming. Charleston, in South Carolina, is another city that should concern government officials. It was the principal port of slave disembarkation in North America. City planners have sought to build an African American museum there, facing the waterfront with views past Fort Sumter toward the Atlantic Ocean, but everything may flood within a century or so. Cities in northeast Brazil, like Recife and maybe Salvador, were leading ports in the transatlantic slave trade and are also at imminent risk of inundation.
Similarly, some ports in the Mediterranean Sea, like Naples and Venice, financed many of the earliest transatlantic slaving voyages in history, but they will soon meet a similar fate as the Africans who perished at sea. Venice, in particular, has long been struggling to keep itself afloat. In northern Europe, Copenhagen, Helsinki, and possibly Edinburgh participated in the traffic variably, but they are also at risk of inundation. Ports in three African regions can flood in a century or so: Upper Guinea, especially the coast stretching from Guinea to Liberia; the Bight of Biafra in southeast Nigeria; and the East African coast comprehending Tanzania and Mozambique. All of these regions were once deeply engaged in the transatlantic trade, with the latter also involved in the Indian Ocean traffic. Northern Mozambique just had a taste of what is to come, after a cyclone inundated communities miles inland last year.
Other ports have more time, but not too much. If everything remains the same, they will submerge within a millennium. In fact, a lot of them will do so by half that time. The entire coast of New England, from where a significant share of the US slave trade was organized, will be underwater within five centuries, including cities like Boston and New York. The Hague, the principal port of departure for ships flying Dutch colors, will submerge within the same period, a quite dramatic outcome, considering that much of the Netherlands is below sea level and the Dutch have long fought hard to prevent inundation. The Netherlands is no doubt the country with the most sophisticated technology in flood prevention. Ports in northern Brazil, like Belém, at the mouth of the Amazon River, and São Luís have little chances of surviving the rising tide. Similarly, ports in the Congo area as well as in southern Africa have their days counted. Citizens of Cape Town, in particular, will soon find themselves pressed against the mountains facing the raging sea.
Unfortunately, data for the Caribbean islands are lacking, but judging from the information available for the Gulf of Mexico, the future is far from bright or, for that matter, dry. Ports there are likely to sink within a millennium. Although scientists debate whether the incidence of hurricanes ravaging the Caribbean has increased over the years, they seem to agree that their intensity has done so, as Cuba, Haiti, Puerto Rico, and the Bahamas have recently witnessed.
It is a bitter irony that many of the ports most deeply involved in the traffic are also among the last to sink. Ports in the Irish Sea, like Dublin, Liverpool, and maybe Bristol, will not flood before the next four millennia. Liverpool alone outfitted some 4,500 voyages, which transported about 1.4 million slaves. It was Britain’s greatest slaving port. London, safe up the Thames River, will remain above water for the next seven millennia. Most if not all of France’s ports will take several millennia to sink, including Nantes, la Rochelle, and Bordeaux. Lisbon in Portugal, as well as Seville, Cádiz, and Barcelona in Spain were pioneers in the transatlantic trade but will remain dry for many millennia to come. Luanda in Angola was by far the largest port of slave embarkation, but will take about two millennia to flood. Rio de Janeiro, its converse in the Americas, received an estimated 2.3 million enslaved Africans between the sixteenth and nineteenth centuries. Rio’s Valongo Wharf recently entered UNESCO’s list of World Heritage Sites. Nevertheless, the sea will claim it no earlier than three to four millennia. Lagos in Nigeria, as well as Montevideo in Uruguay, can be worry free for the next eleven millennia. Although many ports of the US South will flood within a thousand years, others, like Pensacola and Wilmington, will have a lot more time to prepare themselves for the impending calamity.
Slowly but surely all of these ports will sink one day. Scientists are well aware from where flood will come. They monitor nineteen basins containing sufficient water to inundate different places all over the world, including the former ports of the transatlantic slave trade. Much of the water at these basins is presently frozen. However, as temperatures increase, it will melt, flow into the sea, and then gradually swallow one port after another. Three of these basins are particularly concerning, not only because of the amount of water that they contain, but also because the Earth’s movements will deliver their contents directly to the ports in question.
Greenland poses by far the greatest threat. Located between the Arctic and Atlantic oceans, the continent-size island has an area of 2.2 million km2 (836,330 mi2), of which about 80 percent is covered by an ice sheet 1.5 km thick. Combined, Greenland’s glaciers and ice sheets increase the sea levels of the former ports of the slave trade by an average of half a millimeter per year. Antarctic is the second greatest menace. Although distant, the world’s southernmost continent has an area of 14.2 million km2 (5.5 million mi2), of which 98 percent is covered by an ice sheet averaging 1.6 km (1 mi) thick. It has about 90 percent of the world’s ice and increases the sea levels of the former trade ports by a third of a millimeter per year. Alaska seems too far to have any influence in this process, but the available data indicate that it raises the ports’ sea levels by a tenth of a millimeter per year. All other basins contribute in some way or another, but not to the same extent as these three.
In view of such a prospect, what, if anything, will happen to the way we think, remember, or memorialize the slave trade? The traffic lasted about 350 years. The last documented ship to cross the ocean did so in 1866-67. It has been thus approximately 155 years since the traffic ended. Nevertheless, the legacies of the trade are still all around us and will likely continue so in the next couple of centuries. Consequently, the inundation of ports like Charleston, New Orleans, and Recife may bring an acute sense of loss or consternation, which could briefly revive public interest in the history of the trade. By contrast, in half a millennium or more, people will look at that most tragic event from a very different angle. The distance in time might afford some detachment, making historians talk about the trade in a similar way they currently refer to slavery in Antiquity or the Middle Ages. Several millennia down the road is simply too far to make any conjectures. Should all remain the same, most if not all ports associated with the trade will be underwater. Our preoccupations will have changed. We as a species might not be around anymore.
In 1869, Antônio de Castro Alves, a Brazilian poet, cried in his most famous poem, “The Slave Ship:”
Lord God of the unfortunate!
Tell me, Lord God!
If it is madness… or truth
So much horror under the skies?!
Oh sea, why do you not erase
With the sponge of the waves,
From your mantle, this blot?…
Stars! Nights! Tempests!
Roll down from the immensity!
Sweep the seas, typhoon!
Brazil, the single largest destination for enslaved Africans carried across the Atlantic, had by then closed its ports to the traffic some 20 years earlier. The sea never really had a chance of answering the poet’s cry. Moreover, on a planetary scale, everything moves at a slower pace. Thanks to recent human activity, however, the time for reckoning is not very far. Except that, instead of ships, the sea will claim entire ports.
Daniel B. Domingues da Silva is associate professor of African History at Rice University. He is the co-manager of Voyages: The Trans-Atlantic Slave Trade Database and author of the book The Atlantic Slave Trade from West Central Africa, 1780-1867 (New York: Cambridge University Press, 2017).