The Heat Before the Cold

[Guest guest]

http://www.nytimes.com/2002/04/18/opinion/18JOYC.html

April 18, 2002

The Heat Before the Cold

By TERRENCE JOYCE

WOODS HOLE, Mass. - This week's unexpected heat wave across much of the

Northeast and Midwest, coupled with recent reports about the surprisingly

fast collapse of an Antarctic ice shelf the size of Rhode Island, has

heightened fears of a long-term rise in temperatures brought about by global

warming. But this fear may be misguided. In fact, paradoxically, global

warming could actually bring colder temperatures to some highly populated

areas like Eastern North America and Western Europe.

Here's what might happen: In the North Atlantic, a 10-foot layer of fresh

water - some of which may be coming from melting ice in the Arctic - has

been accumulating and lowering the salinity of the ocean to depths of more

than a mile for the past 30 years. Fresh water in the ocean may not sound

cataclysmic, but it can upset the ocean currents that are the key to our

planet's climate control system.

In February, oceanographers presented new evidence that this northern

freshwater buildup could alter currents in a way that would cause an abrupt

drop in average winter temperatures of about 5 degrees Fahrenheit over much

of the United States and 10 degrees in the Northeast. That may not sound

like much, but recall the coldest winters in the Northeast, like those of

1936 and 1978, and then imagine recurring winters that are even colder, and

you'll have an idea of what this would be like. This change could happen

within a decade and persist for hundreds of years.

Under normal circumstances, the famous warm waters of the Gulf Stream,

carrying heat absorbed in the tropics, move up the East Coast of the United

States and southeastern Canada and then angle toward Europe, warming the

overlying atmosphere and surrounding land as they go. As the Gulf Stream

system carries warm, salty water north, the atmosphere cools it, making it

dense enough to sink to great depths. The plunge of that great volume of

water helps propel a global system of currents sometimes called the great

ocean conveyor. But add too much fresh water, and North Atlantic waters

become less salty and less dense. They stop sinking. The Gulf Stream slows

or is redirected southward. Winters in the North Atlantic region get

significantly colder.

Changes in the conveyor were responsible for some of the most noticeable

climate changes in scientific history. About 12,000 years ago, as the earth

emerged from the most recent Ice Age and the North Atlantic region warmed,

an influx of fresh water - perhaps from melting ice sheets - shut down the

great conveyor and plunged much of the Northern Hemisphere back into ice-age

conditions that lasted 1,000 years. About 500 years ago a reduction of the

ocean conveyors may have turned the climate in northern Europe and the

northeastern United States much colder, during what became known as the

Little Ice Age, which lasted for about 300 years. In America, the Little Ice

Age coincided with the notorious winter at Valley Forge.

There is not enough evidence for scientists to know for sure whether the

influx of fresh water in the North Atlantic has come from an already altered

ocean circulation, changes in rainfall patterns or rivers, or glacial and

Arctic Ocean ice. We don't know the exact threshold at which sinking, and

the great ocean conveyor, could stop. A global ocean-observing system would

greatly enhance our ability to monitor changes that can spawn major,

long-lasting climate shifts like these and lead to reliable predictions of

what may follow. But the evidence we do have suggests that global warming

could actually lead to a big chill.

Terrence Joyce is a senior scientist and chairman of the department of

physical oceanography at Woods Hole Oceanographic Institution.

[Guest guest]

Barbara,

Thanks for this great story. I have been working on a

book since 1992, called EL NINO, WEATHER OR NOT?

So I find any altercation in climate factors

fascinating of course.

Thanks for the update,

Carroll-Bower, NTMC

www.geocities.com/marbme12/NTMC.html

--- bherk@... wrote:

>

http://www.nytimes.com/2002/04/18/opinion/18JOYC.html

>

> April 18, 2002

>

> The Heat Before the Cold

>

> By TERRENCE JOYCE

>

> WOODS HOLE, Mass. - This week's unexpected heat wave

> across much of the

> Northeast and Midwest, coupled with recent reports

> about the surprisingly

> fast collapse of an Antarctic ice shelf the size of

> Rhode Island, has

> heightened fears of a long-term rise in temperatures

> brought about by global

> warming. But this fear may be misguided. In fact,

> paradoxically, global

> warming could actually bring colder temperatures to

> some highly populated

> areas like Eastern North America and Western Europe.

>

> Here's what might happen: In the North Atlantic, a

> 10-foot layer of fresh

> water - some of which may be coming from melting ice

> in the Arctic - has

> been accumulating and lowering the salinity of the

> ocean to depths of more

> than a mile for the past 30 years. Fresh water in

> the ocean may not sound

> cataclysmic, but it can upset the ocean currents

> that are the key to our

> planet's climate control system.

>

> In February, oceanographers presented new evidence

> that this northern

> freshwater buildup could alter currents in a way

> that would cause an abrupt

> drop in average winter temperatures of about 5

> degrees Fahrenheit over much

> of the United States and 10 degrees in the

> Northeast. That may not sound

> like much, but recall the coldest winters in the

> Northeast, like those of

> 1936 and 1978, and then imagine recurring winters

> that are even colder, and

> you'll have an idea of what this would be like. This

> change could happen

> within a decade and persist for hundreds of years.

>

> Under normal circumstances, the famous warm waters

> of the Gulf Stream,

> carrying heat absorbed in the tropics, move up the

> East Coast of the United

> States and southeastern Canada and then angle toward

> Europe, warming the

> overlying atmosphere and surrounding land as they

> go. As the Gulf Stream

> system carries warm, salty water north, the

> atmosphere cools it, making it

> dense enough to sink to great depths. The plunge of

> that great volume of

> water helps propel a global system of currents

> sometimes called the great

> ocean conveyor. But add too much fresh water, and

> North Atlantic waters

> become less salty and less dense. They stop sinking.

> The Gulf Stream slows

> or is redirected southward. Winters in the North

> Atlantic region get

> significantly colder.

>

> Changes in the conveyor were responsible for some of

> the most noticeable

> climate changes in scientific history. About 12,000

> years ago, as the earth

> emerged from the most recent Ice Age and the North

> Atlantic region warmed,

> an influx of fresh water - perhaps from melting ice

> sheets - shut down the

> great conveyor and plunged much of the Northern

> Hemisphere back into ice-age

> conditions that lasted 1,000 years. About 500 years

> ago a reduction of the

> ocean conveyors may have turned the climate in

> northern Europe and the

> northeastern United States much colder, during what

> became known as the

> Little Ice Age, which lasted for about 300 years. In

> America, the Little Ice

> Age coincided with the notorious winter at Valley

> Forge.

>

> There is not enough evidence for scientists to know

> for sure whether the

> influx of fresh water in the North Atlantic has come

> from an already altered

> ocean circulation, changes in rainfall patterns or

> rivers, or glacial and

> Arctic Ocean ice. We don't know the exact threshold

> at which sinking, and

> the great ocean conveyor, could stop. A global

> ocean-observing system would

> greatly enhance our ability to monitor changes that

> can spawn major,

> long-lasting climate shifts like these and lead to

> reliable predictions of

> what may follow. But the evidence we do have

> suggests that global warming

> could actually lead to a big chill.

>

>

> Terrence Joyce is a senior scientist and chairman of

> the department of

> physical oceanography at Woods Hole Oceanographic

> Institution.

>

>

>

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