Sea level rise: Everything you need to know

This article has been updated.

Homes, livelihoods and, ultimately, lives are under threat from rising sea levels. Indeed, the United Nations (UN) calls it "a global crisis" - and one that is impacting 1 billion people worldwide.

Here’s what you need to know.

Sea level rise refers to the increase in the average height of the ocean’s surface, measured from the centre of the Earth. This phenomenon is primarily driven by two main factors: the melting of glaciers and ice sheets, and the thermal expansion of seawater as it warms. As global temperatures rise due to climate change, ice sheets in Greenland and Antarctica are melting at an accelerated rate, contributing significantly to sea level rise.

Additionally, as seawater warms, it expands, further increasing the sea level. This rise in sea level is a critical indicator of climate change, with far-reaching impacts on coastal communities, ecosystems and economies worldwide.

There was an unexpectedly fast rising of the global sea level in 2024, NASA-led analysis has found. Scientists were anticipating a rise of 0.43 centimetres, but instead recorded a rate of 0.59cm.

Pacific island nations like Tuvalu, Kiribati and Fiji have been battling rising sea levels for years now and NASA predicts they will experience a further 15cm of sea level rise in the next three decades, even if greenhouse gas emissions are brought under control.

Representatives from small-island and low-lying countries came together for the UN General Assembly’s (UNGA) High-Level Week in 2024, which for the first time featured a dedicated meeting on Sea Level Rise to address this urgent issue.

“Today is our historical opportunity to turn the global tide and to embark on a common path that secures prosperity, dignity and rights to all affected countries and communities,” said the Prime Minister of Tuvalu.

The key initiatives discussed at the meeting were:

Traditionally, sea level is measured with a tide gauge, which you can see in ports and harbours around the world. But now satellites can carry out this task more accurately by bouncing radar signals off the sea surface to measure changes in sea level.

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

The World Economic 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.

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 9 billion litres of ice an hour, according to the Geological Survey of Denmark and Greenland.

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.

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.

The two main factors causing sea level rise are melting ice from glaciers and seawater expanding because of rises in global temperatures, according to 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 2023/2024.

Since 1971, oceans have absorbed over 90% of excess heat in the Earth system caused by rising greenhouse gas emissions.

Climate change is the primary driver of global sea level rise.

As the Earth’s temperature increases, the polar ice caps and glaciers melt, releasing vast amounts of water into the oceans. This melting ice contributes directly to the rising sea levels.

Furthermore, the warming of the ocean causes the water to expand, a process known as thermal expansion, which also contributes to sea level rise.

The relationship between sea level rise and climate change is complex. Understanding it is crucial for predicting future sea level rise scenarios and developing strategies to mitigate its impacts.

As global warming continues, the rate of sea level rise is expected to accelerate, posing significant challenges for coastal regions around the world.

In the Forum's Global Risks Report 2025, 'Critical change to Earth systems' is the third-biggest threat to the world in the coming decade - and sea level rise from collapsing ice sheets is identified as a key contributing factor.

The effects of global sea level rise are profound and multifaceted, impacting both human and natural systems. Rising seas threaten infrastructure, including roads, bridges and buildings, leading to increased costs for maintenance and repair.

As coastal flooding becomes more frequent and severe, it will exacerbate erosion and cause saltwater intrusion into freshwater sources, which can compromise drinking water supplies and agricultural productivity. The Forum's Water Futures: Mobilizing Multi-Stakeholder Action for Resilience white paper addresses the issue of water pollution as a result of extreme water-related events and lays out five pathways to water resilience.

Additionally, sea level rise poses a significant threat to coastal ecosystems such as mangroves, coral reefs and salt marshes, which provide critical habitats for numerous species.

The displacement of people living in low-lying areas due to rising seas can lead to social and economic challenges, including loss of property, livelihoods and increased pressure on social services.

Addressing these impacts requires comprehensive adaptation strategies to protect vulnerable communities and ecosystems.

The economic and social impacts of sea level rise are significant and far-reaching. Rising seas can lead to increased costs for coastal protection measures, such as building sea walls and surge barriers, and repairing damage to infrastructure.

The loss of property and livelihoods due to coastal flooding and erosion can have devastating effects on communities, particularly in vulnerable regions. Additionally, sea level rise can exacerbate social and economic challenges by displacing people, disrupting economic activities and straining social services.

For example, communities that rely on tourism, fishing and agriculture may face significant economic losses as rising seas threaten their way of life.

Understanding these economic and social impacts is critical for developing effective adaptation strategies and mitigating the effects of sea level rise on vulnerable populations.

Throughout Earth’s history, sea levels have fluctuated significantly, with major changes occurring during the last ice age and the subsequent warming period. However, the current rate of sea level rise is unprecedented.

Since 1890, the global average sea level has risen by approximately 21-24cm, a rate much faster than historical averages, according to the US National Oceanic and Atmospheric Administration. This rapid increase is largely attributed to human-induced climate change, driven by the burning of fossil fuels and the resulting increase in greenhouse gas emissions.

Understanding past sea level rise and its historical context is essential for predicting future changes and developing effective adaptation strategies.

By studying historical data, scientists can better understand the natural variability of sea levels and the extent to which current trends are influenced by human activities.

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.

NASA says the East Coast and Gulf Coast of the US, as well as Asia and islands, are at high risk from the rising ocean. But it's not just the changing sea level that's a threat, it says. "Storm surges are amplified by sea-level rise, causing them to hit higher water levels and allowing the surges to reach farther inland".

According to Reuters, sea levels around Tonga are rising at almost twice the global average rate. In Europe, sea level rise is expected to go above 10cm "prior to 2050", says the European Environment Agency.

While 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.

Developed nations need to double climate adaptation finance to at least $40 billion a year, according to the Glasgow Climate Pact. But even if this was achieved, the adaptation finance gap of $187-359 billion per year would only be reduced by 5%, says the United Nations Environment Programme.

In the meantime, countries and cities around the world are 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.

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, while six have already been moved to safer ground, The Guardian reports.