When discussing how climate change impacts the Baltic Sea, marine scientist Tarmo Soomere says there are two aspects to consider. One is how climate change affects the marine environment and its functioning. The other is how changes in the Baltic Sea's coastlines indicate that the climate has changed. Soomere and his team study the latter.

For example, the extent of climate change in the Baltic Sea can be understood through rising water temperatures. Soomere explained that last spring and summer, the sea temperature during a certain period was about 10 degrees warmer than the multi-year average. Another clear change is the decrease in ice cover. Over the past hundred years, the duration of ice coverage has shortened by nearly two months.

The weaker the sea ice that forms, the more easily the wind pushes it toward Finland, increasing the workload for Finnish icebreakers. "If the ice disappears entirely, wave energy increases by one and a half times. This means that those who have built houses on the shore will soon find themselves in deep water. Likewise, those who use maritime routes will have to dredge waterways more frequently," the marine scientist explained.

Warmer water temperatures also have environmental consequences. The northern part of the Baltic Sea frequently suffers from oxygen deficiency, which is exacerbated by climate warming. When the surface layer is fresher and warmer, while the deeper layer is colder and saltier, the lighter warm freshwater does not push oxygen-rich water to the seabed. As a result, less oxygen reaches the seafloor, endangering marine life as oxygen levels become insufficient for aquatic organisms.

From a coastal perspective, it is important to consider how water levels, waves, and ice — or the lack thereof — interact. Soomere explained that the Baltic Sea is a young sea, just 10,000 years old in its current boundaries. This means that its coastlines are still developing rapidly.

"One peculiarity of the Baltic Sea is that in the regions of Estonia, Latvia, and Lithuania, waves hit the shore at a very steep angle. This means that even small waves can transport a significant amount of sand and gravel, several times more than waves of the same height do in the ocean, precisely because of the steeper approach angle," Soomere said.

The direction in which waves travel has changed over time. In other words, storms now more frequently arrive from different directions than before.

"Right now, we are trying to understand exactly what will happen. However, we can already see a very strong sign of climate change in the shifting wind directions. Some new types of storms have emerged, blowing from different directions and shifting sand and gravel along the coast in the opposite direction," he said.

Waves along the Latvian coast are capable of moving up to a million cubic meters of sand and gravel per year. Soomere said this is an enormous amount compared to the open ocean. The decreasing ice cover only amplifies this process because the less ice there is, the more waves there are.

The scientists noted that Estonia is located in a relatively favorable spot. However, in the long run, rising sea levels will affect the region. Along Tallinn's coast, the land rises by about 2–2.5 millimeters per year, which is roughly the same rate at which global sea levels are rising. This, in itself, is not a direct problem.

"The problem arises when storms push water levels extremely high, as we are seeing along Estonia's coasts, especially in the eastern Gulf of Finland and along the Estonian coast of the Gulf of Riga. The annual maximum water level has risen by about a centimeter per year," Soomere explained.

Model calculations allow for an assessment of the situation.

"This rise is the fastest in the entire Baltic Sea and is nearly as rapid as in the so-called fastest-sinking areas of the world. This does not mean that this year's water level will be exactly one centimeter higher than last year's, but it does mean that if the January storm of 2005 were to happen again, the water would no longer just lap at the floor, it would, figuratively speaking, reach the windows," Soomere described.

In other words, storms are now coming from unexpected directions, and the water is reacting accordingly.

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