Can Global Warming Cause Cooling?
While many parts of the world can expect warmer weather, global warming might have the opposite effect in some places. Western Europe is quite warm for its latitude. This is because the Gulf Stream, a warm ocean current, reaches into the North Atlantic. Winds passing over the warm water and onto land have a moderating effect on the climate. For example, the average winter temperature in London, England, is about 4°C (39°F). Calgary, in western Canada, is at about the same latitude but has an average winter temperature of -9°C (16°F). The Norwegian port of Tromso and the Russian port city of Murmansk are ice-free year round even though they are in the Arctic. The Gulf Stream is part of a worldwide circulation of ocean water known as the thermohaline circulation. Thermo refers to temperature and haline to salinity. Temperature and salinity both affect the density of water.
As the Gulf Stream waters flow northward, water evaporates. This causes an increase in salinity because the same amount of salt is now held by less water. At the same time, the waters cool.