Rising sea levels aren’t something most of us notice. Lying on the beach or enjoying a refreshing swim during a recent summer vacation, we would be aware of high and low tides but probably not of whether the height of the water was any different from when we were children. The so-called global mean sea level (GMSL) is a parameter none of us non-marine scientists can measure anyway. But if we lived on a Pacific atoll like Kiribati we’d have an existential interest in high tides and, like the citizens of other Pacific island states, be extremely worried about rising sea levels. So what are the facts?

The facts

140 countries of the world face the sea. Their total coastline is around 1.6m kilometres. Two-thirds of the world’s largest cities are on such coasts and a billion people live on land no more than ten metres above sea level. Unlike other indications of climate change (rising average temperatures, more frequent extreme weather or increasing greenhouse gas emissions, all of which are developments contested by well-known world leaders and a very small body of scientists) GMSL is an uncontested statistic thanks to accurate satellite measurements since 1993. It is also an alarming one. GMSL rose by 2.7–3.5mm a year between 1993 and 2017. That probably doesn’t sound like much, but to raise GMSL by just one centimetre you have to melt some three-trillion tonnes of ice!

The threat of melting ice

As the world gets hotter, melting ice will contribute most to rising sea levels. Just consider what happened when the ice sheets covering western Eurasia and most of North America melted at the end of the most recent ice age: GMSL rose by around 120 metres! Whereas the media focus up to now has been on melting Arctic ice, and in particular the fate of polar bears, the more dramatic future threat will come from the huge ice sheets of Greenland and Antarctica. The science behind melting terrestrial ice sheets is complicated but suffice to say, if the West Antarctica ice sheet were the collapse – and it is already become unstable – GMSL would rise by around 3.5 metres. And of the two Antarctic ice sheets the western one is small compared to the East Antarctica ice sheet.

The predictions

There may be some dispute about just how fast sea levels are rising, but there is general agreement among scientists on the fact that the rate of sea-level rise is increasing due to global warming. The Intergovernmental Panel on Climate Change (IPCC) reports that sea levels rose by about 19cm during the 20th century and expects a rise of about twice that during the 21st century. The authors of a study that investigated forecast sea level rises over 40 years say the IPCC experts tend to err on the side of caution. If sea levels rise by a metre by 2100, little more than the IPCC predicts, the consequences will be dire.

The cost

Island states such as Kiribati – where the average ‘altitude’ of the land is less than two metres – or The Seychelles will pay the ultimate price. But even in developed nations such as the United States the financial impact will be huge. A report published in 2014 estimated that by 2100 property worth between $20-200tn could be at risk of flooding. The Union of Concerned Scientists, an American NGO, estimates that coastal properties worth $1.1tn today could face fortnightly flooding. And what will be the impact on the ocean freight industry, on port infrastructure, and on trading routes?

Endangered ports

Seaports and harbours are, by definition, low-lying structures designed to enable speedy loading and unloading of ocean-going vessels at the interface of sea and land freight. As a result, rising sea levels will impact seaports earlier than most other land-based structures. Some port authorities have taken precautionary action. London’s Thames Barrier, a movable flood defence, was built in response to the fatal North Sea tidal surge in early 1953 that reached 5.6 meters above mean sea level and cost hundreds of lives. It was closed just eight times between 1982 and 1990 but since then the increasing frequency of closures has taken the total figure to 184 (as of March 2019). And concerns are already being expressed that the Thames Barrier may not be high enough to protect future generations of Londoners against flooding.  

Another highly spectacular flood defence measure inaugurated in 1997, the Maeslant Barrier, is at the mouth of the canal leading to Europe’s biggest port, Rotterdam. 80% of that city is below sea level. The Dutch, past masters at building dykes, levees and seawalls (40,000km of them, no less), were also responding to the 1953 disaster that cost thousands of lives and put 9% of the country’s farmland under water. The Maeslant Barrier swings shut whenever the sea surges above three meters. When designing the Barrier, this was considered to be a once-a-decade occurrence. Now it is happening more frequently. The Mayor of Rotterdam is quoted as saying that the rising threat is a result of climate change.

The author of this blog is unaware of similar schemes to tackle the rising sea-level threat at other major seaports. Hamburg, for example, which lost over three hundred of its citizens to a storm surge in 1962, has heightened the dykes along the River Elbe, which connects the Port of Hamburg with the North Sea. The effect of that flood defence measure, however, will be to channel a much greater volume of water into the low-lying port facilities if a high spring tide surge is driven upriver by a powerful northwesterly storm.

The impact on ocean shipping

For the ocean shipping industry one of the most promisingly positive side effects of global warming and melting Arctic ice is the prospect of new shipping lanes opening up through the previously frozen north. In future summers, shipping times between Europe and the Far East will be drastically reduced as containerships safely navigate the Northeast Passage along the Arctic coasts of Norway and Russia. But there is, as yet, no answer to the question of whether these containerships will be able to take on or discharge cargo at existing port facilities when GSML rises significantly.

Global shipping giant Maersk is driving progress towards a carbon-neutral future of ocean freight and associated intermodal logistics. According to CEO Søren Toft, Maersk is aiming for net-zero emissions by 2050 and investing around $1bn a year and engaging more than 50 engineers to develop and deploy energy-efficient solutions. Maersk’s efforts are in line with the IMO’s strategy for reducing greenhouse gas emissions from shipping. But Maersk is well aware that the company cannot go forward alone and is calling for partners to join the search for sustainable solutions in ocean shipping. That will certainly contribute to the global efforts to slow down the rise in greenhouse gas emissions, but will it be enough to stop sea levels from rising further? Probably not. And then we are entitled to ask what port authorities worldwide are doing to improve their flood defences.

Ocean Insights, as the name says, exists to supply business-relevant insights and reliable data. True to our mission, we will continue to keep you informed on issues of existential importance to the ocean freight industry.

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