Climate Action

Sea level rise: Everything you need to know

Two main factors that cause sea level rise are melting ice from glaciers, and seawater expanding because of rises in global temperatures

Two main factors that cause sea level rise are melting ice from glaciers, and seawater expanding because of rises in global temperatures Image: Unsplash/Thomas Vimare

Victoria Masterson
Senior Writer, Forum Agenda
Stephen Hall
Writer, Forum Agenda
Madeleine North
Senior Writer, Forum Agenda
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This article was first published in September 2022 and most recently updated in September 2024.

  • Over 410 million people could be at risk from rising sea levels by 2100 as a result of the climate crisis - global sea levels have already risen by more than 10cm over the last decade.
  • The UN General Assembly (UNGA) is holding a High-Level Meeting on sea-level rise on 25 September to address its existential threats.
  • Climate change, nature and the energy transition will be under the spotlight at the World Economic Forum's annual Sustainable Development Impact Meetings, which coincide with UNGA's General Debate.

"Since the start of the 20th century, global-mean sea level has risen faster than over any prior century in at least the last 3,000 years, and the rate of increase is accelerating," warns 'Surging Seas in Warming World' - a new United Nations (UN) report on the current and future impacts of sea level rise.

It was released in anticipation of the 79th UN General Assembly (UNGA) in New York, which includes a High-Level Meeting on the existential impacts of this pressing global issue.

Homes, livelihoods and, ultimately, lives are under threat from rising sea levels.

By 2100, up to 410 million people could be at risk from coastal flooding as the climate crisis causes sea levels to rise even higher.

Here's what you need to know.

Why is the spotlight on sea level rise now?

For the first time, the UN General Assembly's High-Level Week 2024 will feature a dedicated meeting on Sea-Level Rise on September 25, encompassing four multi-stakeholder thematic panel discussions. Collectively, they will address the legal, financial, socio-economic and scientific aspects of sea-level rise, covering its impacts on livelihoods, adaptation strategies and decision-making processes.

Climate change, nature and the energy transition will also be under the spotlight at the World Economic Forum's annual Sustainable Development Impact Meetings (SDIM24) in New York 23 to 27, which coincide with UNGA's General Debate.

Uniting leaders from politics, business and civil society, SDIM aims to drive innovation on the UN Sustainable Development Goals, focusing on climate action, digital literacy, and economic inclusion. Only 17% of the SDGs are on track, underscoring the urgent need for accelerated progress.

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How is sea level measured?

Sea level is the measurement of the sea’s surface height. Between the 1800s and early 1990s, tide gauges attached to structures such as piers measured global sea level, as research organization the Smithsonian Institution explains.

Now satellites carry out this task by bouncing radar signals off the ocean’s surface. The Forum's work on Amplifying the Global Value of Earth Observation highlights monitoring changing sea levels as a key application of the technology to support vulnerability analysis.

Because local weather conditions and other factors can affect sea level, measurements are taken globally and then averaged out.

NASA chart showing sea level rise 1993-2024
Sea levels have risen by over 10cm between 1993 and 2024. Image: NASA

In 2021, scientists discovered a sea-level "fingerprint" from the Greenland ice sheet, confirming fears about the extent to which ice is melting.

These fingerprints are "detectable patterns of sea level variability around the world resulting from changes in water storage on Earth’s continents and in the mass of ice sheets", according to NASA.

The Greenland ice sheet is now losing around 30 million tonnes of ice an hour, reports The Guardian, and a recent study predicts its total collapse could happen by 2025.

How much are sea levels rising?

With the ice sheet at "a tipping point of irreversible melting", scientists currently expect an unavoidable sea level rise of 1-2 metres.

Global sea levels have already risen by over 10cm between 1993 and 2024, according to NASA, which says sea levels have been rising at unprecedented rates over the past 2,500 years.

The US Space Agency and other US government agencies warned in 2022 that levels along the country’s coastlines could rise by another 25-30cm by 2050.

The global sea level has risen by about 21cm since records began in 1880. While measuring in centimetres or even millimetres might seem small, these rises can have big consequences. This is particularly true where storm surges sweep further inland than they would have previously.

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What causes sea level rise?

Two main factors cause sea level rise. These are melting ice from glaciers, and seawater expanding because of rises in global temperatures, explains the US National Oceanic and Atmospheric Administration.

There are also likely negative feedback loops that could speed up glacier ice melt. For example, the Thwaites Glacier in Antarctica is disintegrating more quickly than anticipated. It’s nicknamed the ‘doomsday glacier’ because sea levels could rise more than three metres without it and its supporting ice shelves.

Heat stored in the ocean is responsible for between a third and half of global sea level rise, NASA says. The past decade has been the ocean’s warmest since at least 1800, and ocean temperatures reached a new high in 2023.

Since 1971, oceans have absorbed over 90% of excess heat in the Earth system caused by rising greenhouse gas emissions, the UN's Surging Seas report reveals.

Which countries will be most affected by rising sea levels?

Bangladesh, China, India and the Netherlands were singled out by the UN in 2023 as being at high risk from rising sea levels, with nearly 900 million people living in low-lying coastal areas in acute danger.

In its Surging Seas report, the organization highlights the dangers facing the communities of the Pacific Small Island Developing States: "The Pacific SIDS, especially those in the western tropical Pacific (e.g., Kiribati, Tuvalu, and the Republic of the Marshall Islands), are particularly vulnerable to SLR [sea level rise] because of: (i) high exposure to tropical cyclones and other tropical storms; (ii) high shoreline-to-land area ratios; (iii) high sensitivity to changes in sea level, waves, and currents; and (iv) its many low-lying coral atolls or volcanically-composed islands."

In Europe, sea level rise is expected to go above 10cm "prior to 2050", says the European Environment Agency.

While recent research in the US has found that almost 1,100 critical buildings in coastal communities could be at risk of monthly flooding by 2050. Some communities could become unliveable within two to three decades, the report says.

Sea level rise is one of the 'critical changes to Earth systems' - the second-highest threat to the world in the coming decade.
Sea level rise is one of the 'critical changes to Earth systems' - the second-highest threat to the world in the coming decade. Image: World Economic Forum Global Risks Perception Survey 2023-2024

How are areas at risk of rising sea levels adapting?

In its Global Risks Report 2024, the World Economic Forum added the category 'Critical change to Earth systems' as one of the top two threats to the world in the coming decade - and sea level rise from collapsing ice sheets is identified as a key contributing factor.

Adaptation is vital, it says, but "efforts are falling short", with a finance gap currently estimated at $194 billion to $366 billion a year.

Countries and cities around the world are nevertheless putting strategies into action. In New Zealand, climate adaptation policies are being designed to ensure public housing is not built near areas prone to climate hazards.

Sea walls, surge barriers and other coastal defences are being built and strengthened in several countries including Denmark, Germany and the United Kingdom.

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What's the World Economic Forum doing about the ocean?

South Korea and the islands of the Maldives in the Indian Ocean are experimenting with floating homes, while China, India and other nations are finding ways to absorb and store storm water for reuse.

More drastic action is taking place in Fiji, where government officials are making plans to relocate whole villages because of rising sea levels - 42 villages have been recommended for relocation in the next five to 10 years, while six have already been moved to safer ground, The Guardian reports.

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The views expressed in this article are those of the author alone and not the World Economic Forum.

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