The North Sea takes up twice as much CO2 along its coasts as previously thought

15 May 2018, by Johannes Pätsch, CEN

Photo: UHH/CEN/T.Wasilewski

Calm or stormy? Wind speed determines how much CO2 the water can take up.

We have a powerful ally against climate change: the oceans. The world’s oceans take up a third of the greenhouse gases that humans pump into the atmosphere as a result of industry and traffic, curbing their effect and buffering climate change. But they are paying the price – the oceans are becoming more acidic, and this is happening on our doorstep, in the North Sea.

As climate researchers at Universität Hamburg’s Center for Earth System Research and Sustainability (CEN), my colleague Maybritt Meyer and I wanted to investigate how much carbon dioxide (CO₂) the North Sea absorbs in a year. To do so we needed two main pieces of information: firstly the concentration of CO₂ in the air compared to that in the water. If the levels are the same, nothing changes. However, the greater the difference – e.g. a high concentration of carbon dioxide in the air and a low concentration in the water – the higher the “pressure” on the CO₂ to dissolve in the water. An international team collected this data during several excursions.

At the same time, wind plays an important role – something we also investigated closely. The more strongly the wind blows, stirring up the water’s surface, the greater the exchange with the atmosphere. By mixing the sea like a whisk, it allows CO₂ to be more effectively absorbed. However, there is no comprehensive data from all points in the North Sea, so how can the wind be incorporated into the calculations?

34 percent more CO2 uptake for the entire North Sea

To date, we have relied on data from a relatively coarse resolution global model that describes the wind speed at one grid point every hundred kilometers. We used this information to calculate how quickly or slowly the water is able to absorb carbon dioxide. But at the coasts, the wind is particularly changeable, which means that this data hardly reflects the reality.

Our partners from the Helmholtz Center Geesthacht are investigating the coasts with higher resolution models. Using what is known as downscaling – a complex computer simulation – it is possible to meaningfully fill the gaps in the data for regions for which there is little information. The Center calculated a new wind data set for us with a grid spacing of five to ten kilometers for the entire North Sea.

We compared this data with measurements from four stations – two near the coast and two on drilling platforms in the open sea. The results show: the wind at the coasts has previously been greatly underestimated! The high-resolution data paints a much more accurate picture. For the open sea, the measurements correspond well with the older wind data.

We recalculated the CO₂ balance – with astounding results: along the coasts more than twice as much carbon dioxide is absorbed as previously assumed. In a year, the entire North Sea took up 34 percent more of the greenhouse gas than thought.

Acidification is in full swing

But what does that mean? We don’t know when the marine carbon dioxide storage will be full. But the more CO₂ an ocean absorbs, the more acidic it becomes. In the North Sea, acidification is in full swing, and the changes in the water’s pH can have a detrimental effect on the plants and animals there: their metabolisms have to adapt, while mussels and crabs can have problems forming their shells.

Using refined methods, we can provide increasingly accurate predictions, many of which demonstrate the dramatic impacts of our actions. Therefore I would like to call on the German Federal Government to adhere to the climate goals agreed in Paris in 2015 and effectively curb greenhouse gas emissions.

This content was first published as a guest article in the newspaper Hamburger Abendblatt in May 2018.

Johannes Pätsch is a computer scientist and North Sea expert at Universität Hamburg’s Center for Earth System Research and Sustainability (CEN).

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