Dear EarthTalk: If the ice caps are melting, what is happening to the salt content of the oceans? And might this contribute to weather patterns or cause other environmental problems?
—George Boyer, via e-mail
It’s true that the melting of the polar ice caps as a result of global warming is sending large amounts of freshwater into the world’s oceans. Environmentalists and many climate scientists fear that if the climate heats up fast enough and melts off the remaining polar ice rapidly, the influx of freshwater could disturb ocean currents enough to drastically change the weather on the land as well.
The Gulf Stream, a ribbon of ocean water that delivers heat from the tropics up to the North Atlantic, keeps northeastern U.S. and northwestern Europe weather much milder than other areas at the same latitude around the globe. In theory, less salt in the ocean could stall out the Gulf Stream and rob some of the world’s greatest civilization centers of their natural heating source, plunging the two continents into a cold snap that could last decades or longer—even as the rest of the globe warms around them.
The Gulf Stream keeps running because the warmer water travelling north is lighter than cold water, so it floats on top and keeps moving. As the current approaches the northern Atlantic and disgorges its heat, it grows denser and sinks, at which point it flows back to the south, crossing under the northbound Gulf Stream, until it reaches the tropics to start the cycle all over again. This cycle has allowed humans and other life forms to thrive across wide swaths of formerly frozen continents over thousands of years. But if too much dilution occurs, the water will get lighter, idling on top and stalling out the system.