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Grain of Salt
Tue Apr 06, 2004
Listen in RealAudio 
Tropical oceans are becoming saltier, a change that could be linked to global climate
change, and might spell colder temperatures for Europe. Hi, I'm Bryan Yeaton, and this
is The Weather Notebook's weekly segment on global climate change.
Scientists have recently found that, near the equator, the Atlantic Ocean is dramatically
saltier than it was 40 years ago, and near the North and South poles, its waters have
become fresher. That's bad news because the freshness of its water is what drives a
large ocean current that helps keep Europe relatively warm.
What's causing the salinity changes? Global warming is probably partly to blame.
Warmer temperatures near the equator create more evaporation, leaving salt behind.
That water -- about five to 10 percent more over the last five decades -- in turn goes into
the atmosphere where it becomes a greenhouse gas, warming the planet still further.
The moisture eventually precipitates out at higher latitudes which causes the ocean's
polar waters to become fresher.
Because salt water is denser than fresh water, it sinks when it arrives in the North
Atlantic. This sinking starts a conveyor belt, drawing warmer tropical water up from the
equator and warming Europe, especially in the wintertime.
So this new fresh water in the North Atlantic threatens the conveyor belt, which could
shut off the European heat pump. Ironically, the effects of global warming could be a
colder North Atlantic and long-term droughts over other areas of the Northern
Hemisphere. In fact, some climatologists have worried about just such a scenario for a
few decades now, and this research is the first sign that something might be
amiss.
Thanks to David Appell for today's story. The Weather Notebook if funded by Subaru
and the National Science Foundation. Extra help comes from Davis Instruments, at
www.davisnet.com. Thanks to Executive Engineer Sean Doucette.
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