Slowing ocean circulation could presage dramatic and chilly
climate change Call it global warming's dirty little secret.
Those much-publicized scenarios of how carbon-dioxide (CO2)
pollution may gradually heat up the earth don't tell you another
key fact: that climate has sometimes changed without warning. It
can go from warm to cold or cold to warm in less than decade,
and stay that way for centuries. Water-circulation data from the
North Atlantic now suggest the climate system may be approaching
that kind of threshold. If man-made warming or natural causes
push it over the edge, the system will chill down many temperate
parts of North America and Europe, even while the planet as a
whole continues to warm. Terrence Joyce, chairman of the
physical-oceanography department at Woods Hole Oceanographic
Institution in Massachusetts, is one of a handful of scientists
trying to raise awareness about this possibility. He says he is
"not predicting an imminent climate change only that once it
started (and it is gettin