What causes sea level rise?

Sea level rise isn’t just some distant sci-fi scenario; it’s happening right now. It’s one of the clearest indicators of climate change, and understanding the causes behind it is crucial as we face the future. So, what causes sea level rise? And what are the main factors driving this change?

Thermal expansion

When water heats up, it expands

The first culprit is thermal expansion, a pretty straightforward concept from physics. Water, like most things, expands when it’s heated. 

Since our oceans are absorbing over 90% of the excess heat trapped by greenhouse gases, the water in them is literally expanding, taking up more space. In fact, about half of the sea level rise over the past 25 years is due to this process alone. 

The warmer the oceans get, the more room they need.

Melting glaciers

Goodbye, mountain ice

Glaciers have been melting for ages, but climate change has seriously sped things up. 

In the past, melting was balanced by snow accumulation during winter. But now, the planet’s warming temperatures mean that glaciers, particularly in places like the Himalayas and the Andes, are losing more ice than they’re gaining. 

This runoff ends up in the ocean, adding more water to the mix and pushing sea levels higher.

Ice sheets in Greenland and Antarctica

The big ice blocks

Ice sheets in Greenland and Antarctica are melting fast, and they’re major contributors to sea level rise. 

Greenland’s ice sheet alone loses about 270 billion tons of ice every year. That’s a staggering amount of water pouring into the ocean. 

On top of that, the ice sheets aren’t just melting from the top down. In some areas, meltwater seeps under the ice, effectively “lubricating” it, causing more chunks of ice to slide into the sea faster than before.

Groundwater pumping

Sinking land makes rising seas worse

Human activities are making things worse in certain areas. 

When we pump groundwater to use in cities or farms, we deplete aquifers. The land above those aquifers sinks, and this relative sea level rise—where the water level increases compared to sinking land—is a serious issue in some places. 

Jakarta, for example, is sinking so fast from groundwater pumping that parts of the city are expected to be under water in the near future.

The local twist

Relative sea level rise

Not all sea levels rise at the same rate everywhere. Local factors like land subsidence (sinking land), erosion, and shifting ocean currents can make the sea rise faster in some regions and slower in others. 

For example, the Gulf Coast of the U.S. is seeing some of the fastest sea level rise, while areas like Alaska are seeing sea levels fall, thanks to geological processes that are lifting the land.

So, what’s the outcome?

Rising seas don’t just mean more beach erosion. They bring with them a host of other problems, especially for coastal communities. 

Storm surges from hurricanes and typhoons are made worse by higher seas, pushing water further inland and causing more destruction. Coastal ecosystems are at risk, too, as saltwater invades freshwater sources and disrupts habitats.

If that wasn’t enough, rising seas threaten infrastructure like roads, bridges, and power plants—especially in low-lying areas. And with some parts of the world expected to see sea levels rise by over a foot by 2050, the pressure to adapt is only growing.

The future of sea level rise

How bad will sea level rise get? That depends largely on what we do about climate change. 

Scientists predict that by 2100, we could see sea levels rise anywhere between 10 and 30 inches. But if we continue to burn fossil fuels without making significant cuts, those numbers could be on the higher end—or worse.

The bottom line is that sea level rise is happening, and it’s not going to stop anytime soon. The good news? While we can’t reverse the clock, we can take steps to slow the process. But it’s going to take global cooperation to make it happen.