Behind the information: monitoring rising seas

Rising seas

“In the picture under, you possibly can see the variations in sea degree from 1993 to 2023. Nearly every thing is mild purple, indicating an increase of about two to 4 millimetres per 12 months, so about 11 to 12 centimetres over that thirty-year interval, with some patches of darker purple the place there may be even greater sea degree rise. You can see this in a number of locations, together with the Atlantic Ocean. Other locations are almost white, that are spots the place there was virtually no rise. And then there are a number of locations, resembling west of South America, which can be blue, indicating a lower in sea degree.

“Generally, when we talk about sea level rise, we think of three main contributors. The first is that the ocean is warming, and because warmer water takes up more space than cooler water, the level of a warmer ocean is higher than that of a cooler ocean. This is known as thermal expansion. It is the same thing that happens to mercury in a thermometer – when the surrounding air heats up, the mercury heats up and expands, so it reaches a higher number on the scale.

“The second contributor is the melting of glaciers, which is when frozen water on land melts and flows into the ocean. It is important to keep in mind that melting glaciers contribute to sea level rise but melting sea ice has almost no impact on sea level. This is because sea ice, which floats on the ocean, displaces the same volume in its frozen state as it does in its liquid state. So, whether sea ice remains frozen or melts, the sea level stays almost the same.

“It is a different story when it comes to the water in glaciers. When frozen, that water stays locked on land. But when a glacier melts, that water ends up in the ocean, causing the sea level to rise.

“The third contributor, which has a very small impact globally but can have a noticeable one locally, has to do with the fact that freshwater is less dense than saltwater. Because glaciers and sea ice are mainly composed of freshwater, melting glaciers and melting sea ice contributes more freshwater to the ocean, raising the sea level.

“What you can see in this map is that although the overall trend is that the sea level is rising, it does not do so homogenously across the globe. The ocean is not static – it is moving all the time. Some variations in sea level are caused by ocean currents and El Niño- and La Niña-related events, which impact the temperature of the ocean and sea level unevenly. So, the 30 years of data that we show here is long-term but not enough to compensate for all the variations.

“I remember a study from one of the main sea level experts on the impact of El Niño on sea level rise. He said that we would need more than 50 years of data to compensate for a very big El Niño. So, despite all the data we have already, we still do not have a long enough time series of data to compensate for all the interannual and decadal variability of the ocean. That being said, the data do show that the sea level is rising, and we have further evidence that indicates this is driven by human activity.”