Imagine that you take a cruise with your family to Scandinavia (the northern European countries of Norway, Sweden, Finland, and Denmark) one winter. The land is covered in snow but the ocean is free of ice, allowing your ship to move through the water easily. You ogle the dramatic Norwegian fjords (steep sided rocky valleys flooded by the sea) and stop at a port for some delicious Swedish glogg (a yummy, hot, spiced drink). You have such a great time that you decide to go back again when you’re an adult. So, fast-forward about 20 years…you’re on the phone trying to make reservations but you can’t find a single cruise line that goes to Scandinavia in the winter! Why not? It turns out that thanks to global warming, ice-free winter waters a thing of the past in Scandinavia. In fact, all northern European coastal ports are now icebound in winter!

Whoa! Back up here! How can global warming cause Europe to get colder? Well, it’s a bit complicated, but if you think you are up for the challenge, keep reading to find out why! The ocean waters around Europe are currently kept warm by one of the largest warm water currents in the world—the Gulf Stream. This current carries warm water from the tropics all the way to Europe, warming the ocean temperatures even in the winter. Without this current, things would get pretty nippy in northern Europe, and many ports would be locked in ice. So how does climate change fit into all this? Well, a special type of ocean circulation called thermohaline circulation drives the Gulf Stream. Thermo- means temperature and –haline means salt. In other words, differences in the temperature and amount of salt in the water keep this circulation running. Cold, salty water in the polar oceans sinks and displaces (shoves aside) warmer, less salty water. This happens because the colder and saltier the water is, the denser (heavier) it is. The displaced water has to go somewhere, so it shoves more water along, driving the world’s ocean currents, including the Gulf Stream. But as the planet warms, the oceans warm too. Sea ice, which has very little salt in it, starts to melt. This adds salt-free water to the polar oceans, which doesn’t sink! As a result, thermohaline circulation has already started to slow down! Scientists fear it may one day grind to a halt if the Earth keeps warming. If this happens, winter ports in northern Europe will be locked up like giant ice cubes!

Yikes! What’s a poor planet to do? Tune into tomorrow’s post as our sea ice series continues!