The oceans are rising faster than ever before, mainly because of human activities warming the planet, and this will continue to affect coastal communities worldwide.

Key idea: The two main drivers of sea level rise are the expansion of warming ocean water and the melting of land ice.

So, what is making the sea level rise? There are two main reasons. First, as the Earth gets warmer, the ocean water itself gets warmer. Just like most things, water expands when it heats up. This is called thermal expansion. Think of it like heating a pot of water on the stove; the water level goes up slightly even before it boils, simply because the water molecules are moving faster and taking up more space.

The second big reason is the melting of ice. Our planet has huge amounts of ice stored in glaciers (large rivers of ice in mountains) and ice sheets (vast layers of ice covering land, like in Greenland and Antarctica). As the world warms, this ice melts, and the water flows into the oceans, adding to their volume. Between 1993 and 2018, melting ice and thermal expansion each contributed about 42 to 44 percent of the total sea level rise.

It is important to understand that sea level rise does not happen instantly with warming. There is a delay, sometimes decades long, because the oceans take a while to heat up completely. This means that even if we stopped all warming today, sea levels would continue to rise for some time due to the warming that has already happened.

“The speed of sea level rise has dramatically increased, directly linked to climate change caused by human activities.”

Key idea: Scientists use satellites and tide gauges to accurately measure sea level changes, confirming the current rapid rise is unprecedented in recent history.

Scientists use different methods to figure out how much the sea has risen and how much more it will rise. One way is through satellite measurements. Since the early 1990s, satellites like TOPEX/Poseidon have been constantly orbiting Earth, bouncing microwave pulses off the ocean surface. By timing how long it takes for the pulse to return, they can measure the exact height of the sea surface with incredible accuracy.

Another long standing method involves tide gauges. These are instruments placed along coastlines that measure the local water level over time. While satellites give us a global picture, tide gauges provide historical data, with some records going back hundreds of years. For example, the oldest continuous measurements started in Amsterdam in 1675!

By combining these methods, scientists have confirmed that the sea level rise we are seeing today is truly unusual. Data shows that sea level has not risen this fast in at least the last 3,000 years. This helps us understand that the current changes are not just part of a natural cycle, but something new and accelerated.

“By combining satellite data and tide gauge records, scientists have confirmed that the sea level rise we are seeing today is truly unusual.”

Key idea: Future sea level rise depends on greenhouse gas emissions, with higher emissions leading to much greater and more rapid increases.

Looking ahead, how much the sea will rise depends heavily on how much more greenhouse gas emissions we release into the atmosphere. Scientists create different future scenarios, from very low emissions to very high emissions, to predict the range of possible outcomes.

For example, if we make very deep cuts to emissions, sea level rise might slow down between 2050 and 2100. In this best case, sea levels could still rise by about 30 centimeters (1 foot) to 1 meter (3.3 feet) by the year 2100. However, with high emissions, the rise could be much greater, potentially reaching 1.9 meters (6.2 feet) by 2100.

Over an even longer period, like the next 2,000 years, the numbers become even more dramatic. If global warming stays at 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre industrial levels, sea levels could rise by 2 to 3 meters (7 to 10 feet). But if warming reaches 5 degrees Celsius (9 degrees Fahrenheit), we could see a staggering 19 to 22 meters (62 to 72 feet) of sea level rise. This shows the huge impact our choices today will have on the future of our planet.

One common misconception is that sea level rise will stop as soon as we reduce emissions. However, due to the ocean's slow response to warming, sea levels will continue to rise for centuries, even after emissions are cut, making long term planning crucial.

“If warming reaches 5 degrees Celsius, we could see a staggering 19 to 22 meters of sea level rise over the next 2,000 years.”

Key idea: Sea level rise increases flooding, intensifies storm surges, causes coastal erosion, and contaminates freshwater, threatening millions of people and vital resources.

The impact of rising seas is not just a distant problem; it affects people and places right now. Coastal communities face more frequent flooding, even on sunny days during high tides. This is often called 'nuisance flooding' but can cause significant disruption.

Rising sea levels also make storm surges much more dangerous. A storm surge is when strong winds from a storm push water towards the shore, causing sea levels to temporarily rise much higher than normal. With a higher starting sea level, these surges can reach further inland, causing more damage to homes, businesses, and infrastructure.

Beyond immediate flooding, rising seas lead to increased coastal erosion, where land is washed away. It also causes saltwater to seep into freshwater sources, like underground water supplies and agricultural fields, making the water unusable for drinking or growing crops. This can lead to food shortages and force people to leave their homes.

Tens of millions of people living in low lying coastal areas are already at risk of annual flooding by 2050. Without significant changes, this number could grow to hundreds of millions by the end of the century. Cities like Miami, Rio de Janeiro, and Shanghai are particularly vulnerable.

Key idea: Sea level rise disproportionately affects vulnerable communities, highlighting issues of environmental justice and the unequal distribution of resources for adaptation.

The effects of sea level rise are not felt equally by everyone. This is an issue of environmental justice. Often, communities that are already struggling financially or socially, such as low income areas or Indigenous communities, are hit the hardest. They might live in areas more exposed to flooding and have fewer resources to prepare for or recover from these events.

For example, research shows that adaptation strategies, like building sea walls, are often prioritized in areas with higher property values. This means that wealthier areas get more protection, while poorer communities might be left to face the impacts alone, or even be forced to relocate.

This unequal impact can lead to the displacement of entire communities, disrupting cultural practices and social structures that are deeply tied to ancestral lands. It highlights how environmental challenges like sea level rise are connected to existing social and economic inequalities.

Societies can try to adapt in different ways. Some approaches are 'hard' solutions, like building massive sea walls or moving entire towns away from the coast (called 'managed retreat'). Other 'soft' approaches include restoring natural defenses like sand dunes and mangrove swamps, which can absorb wave energy. Often, a combination of these strategies is needed, but poorer nations often struggle to afford the same protective measures as richer ones.