4 facts about sea level rise

1. The global rate of sea level rise has increased by 50% in the past 30 years.

The rate of global sea level rise has increased by more than 50% when comparing the rate in the 1990s to the most recent 10 years. That means that the global sea level has been rising 1.5 times faster in the latest decade than during the first ten years of satellite radar altimeter measurements, which determine the ocean surface height (aka sea level). To quantify this: between 1993 and 2002, the global average sea level rose by 24 mm, whereas between 2014 and 2023, it increased by 36 mm.

Jason Box also highlights that while we tend to focus on the gradually upward creeping curves of sea level, coastal inundation already happens with today’s sea level rise under high tides and storm surges.

2. Greenland is the largest global regional source of sea level rise – and the amount of ice it’s losing will surprise you.

The Greenland ice sheet holds 90% of the total land ice volume in the Arctic[1], that is 23 times the current volume of all glaciers around the world. Even if only a small fraction of the Greenland ice is lost, it’s important given that Greenland is the largest regional source of sea level rise. Currently, Greenland loses around 270 gigatons (for reference: one gigaton is a billion metric tons) of its ice mass per year. Jason Box has developed a tool that helps to visualize this enormous amount of ice:

“The annual ice loss of the Greenland ice sheet is the equivalent of each person on the planet filling a bathtub with water every day of the year! That is around 8 billion bathtubs that can hold 100 liters,” Jason Box shares.

While Greenland dominates the Arctic’s contribution to global sea-level rise, land ice in other regions, such as Alaska and Arctic Canada, also plays a significant role. Alaska accounts for 27% of the Arctic’s sea-level contribution, while Arctic Canada adds 12%.

“Collectively, all Arctic land ice masses lose approximately 350 gigatons of ice each year. This amount of meltwater could not only submerge Manhattan Island entirely but could also bury it under a water mass 3 kilometers deep every year,” states Jason Box.

Per second (!) all Arctic glaciers and ice sheets together lose ca. 9.5 tons of ice. “This equals 1.5 times the flow rate of the Danube River during the recent flooding events and 145 times the flow rate of the river Thames,” he explains.

3. Sea-level rise affects coastal communities across the globe, but the global South is disproportionally affected.

The sea level doesn’t rise equally around the globe. In the tropics, the sea level for example rises 30% more than the global average. Why is that the case? Prof. Box outlines two main reasons:

The gravitational fingerprint: When large ice masses melt, they alter the Earth’s gravitational field. As the Greenland ice sheet loses ice, its gravitational pull weakens, causing nearby ocean waters to move away from Greenland towards faraway areas of the planet. This phenomenon, known as the ‘gravitational fingerprint’, results in uneven sea-level changes across the globe.

The land is not rising - compared to, for example, Scandinavia. Parts of Denmark, Norway, Sweden and Finland were covered under a heavy ice sheet during the most recent ice age. As the ice retreated, the landmasses started rising. This is called a postglacial rebound. This rebound is to some extent counteracting the effects of sea level rise in the region. Yet, as the tropics were not covered in ice, they do not experience this rebound effect.

Major cities in the Western Northern Hemisphere, including London, Copenhagen, Dublin, and New York, are projected to experience significant sea-level rise—potentially up to 2 meters by the end of the century if global temperatures would increase by 5 degrees Celsius[2]. “While this will pose costly challenges for northern cities, they generally have more resources to adapt compared to cities and countries in the Global South. Additionally, large river deltas like the Mekong, Nile, and Niger, which are critical agricultural regions feeding millions of people, may be far less resilient to the impacts of rising sea levels,” says Jason Box.

4. Current climate policies are not managing the risk appropriately – most people would not accept this risk factor if their lives would be at stake

There’s a 1:20 risk (5%) that the worst-case scenarios for global sea level rise will happen by the middle or end of this century, which would include drastic destabilization of the Greenland and Antarctic ice sheets. While at the moment, the likelihood is low, the stakes extremely high. Imagine if someone told you that there’s a 1:20 risk that the plane you are about to board could crash – would you go on board?

Current climate policies do, according to Jason Box, not sufficiently reflect the risk of rapid sea level change. Why is that the case? “Because if climate policy would accurately manage risk, this implies an enormous monetary investment, which society probably cannot afford. Instead, we see a widening gap between the commitments parties to the UNFCC have made and the reality of actions being taken,” he says.