"The Big Chill", Why an Ice age may come within 20 yrs.. was Re: NRC: Warmere aarde niet door zon

[Henk op xp]

REPLY TO: D66 at nic.surfnet.nl

Steven Rieder schreef:
>  REPLY TO: D66 at nic.surfnet.nl
>
>  Uit de NRC van dinsdag en NRC Next van woensdag:
>
> > Minder vlekken, minder straling Door onze redacteur Karel Knip
> >
> > *Als de zon van invloed was op opwarming, zou de aarde nu juist
> > afkoelen*

"The Big Chill" - Documentary

http://www.youtube.com/watch?v=7FQptadK8rE
Why an Ice age may come to Britain within 20 yrs - Pt 1 of 4

http://www.youtube.com/watch?v=D0EeTgTHHrs
Why an Ice age may come to Britain within 20 yrs - Pt 2 of 4

http://www.youtube.com/watch?v=JHZWcrx9aa0
Why an Ice age may come to Britain within 20 yrs - Pt 3 of 4

http://www.youtube.com/watch?v=VZz8_3m8L3M
Why an Ice age may come to Britain within 20 yrs - Pt 4 of 4

"
A growing number of scientists believe we could have our future climate 
completely wrong. The ice age is coming to UK & EU within 20 yrs as Gulf 
conveyor stops. The conveyor is rapidly turning shutting down due to 
Greenland's glaciers melting as a result of global warming. Eventually 
numerous large rivers will be sending huge amounts of fresh water into 
the conveyor causing it to cease altogether which means no more warm 
water flows north.

Another side effect of the Gulf conveyor ceasing will be severe droughts 
in many areas around the equator causing a huge displacement of people. 
The Amazon rainforest will turn to grassland and many other 
catastrophies will result.

Film excerpts are from "The Big Chill" - Documentary

Documentary narrated by Jack Fortune.
...
"

http://www.bbc.co.uk/science/horizon/2003/bigchilltrans.shtml
"
The Big Chill - transcript

NARRATOR (JACK FORTUNE): In thirty years time they say Britain’s summers 
could be like the South of France. By the end of the century we could be 
as hot as Greece. This they say is what global warming could bring us. 
But a growing number of scientists believe we could have our future 
climate completely wrong.

PROF BILL MCGUIRE: I can only describe it as catastrophic. It’s clearly 
going to influence every single one of us every day of our lives.

Dr RICHARD WOOD: You could expect to see sea ice off the coast of South 
East England, probably several miles off shore.

BOB GASGOSIAN: The implications are huge. The economic implications, the 
political implications, and the national security implications, for all 
countries.

NARRATOR: If these scientists have it right forget the Riviera, Britain 
could be heading for a climate like Alaska’s. And it could all happen in 
the just the next twenty years.

NARRATOR: In the Atlantic waters north of Scotland a fisheries 
researcher was the first to record a warning from the deep. Bill Turrell 
has spent his career studying the ocean currents. Until recently his 
concern has been how they affect fish stocks. But ten years ago he began 
to see something in the water that really alarmed him.

DR BILL TURRELL (Marine Laboratory, Aberdeen): We really worried when we 
saw these results, we’d never seen a change like this ever before. 
Changes that don’t occur quickly and don't stop quickly.

NARRATOR: Turrell believes that he has found evidence that a climate 
catastrophe could be heading right towards us.

DR BILL TURRELL: These changes are fundamental, they’re substantial. 
They are going to impact our climate and the climate our children have 
to live in.

NARRATOR: If he is right then Britain could be heading for a massive 
drop in temperatures. It seems we could be heading for something like an 
ice age. The ice ages were one of the greatest forces nature has 
unleashed on our planet.

PROF BILL MCGUIRE (University College London): They simply were the most 
dynamic, destructive phenomenon that’s ever hit the planet. They involve 
glaciers hurtling down from mountainous regions, pouring out from the 
polar regions and devastating everything in their paths, grinding rock 
to nothing, lowering mountains, filling valleys.

NARRATOR: More than twenty times in the earth’s history ice sheets have 
come down from the North Pole, the last one struck a hundred thousand 
years ago. Britain was buried in a tomb of ice.

PROF BILL MCGUIRE: Effectively they wiped the slate clean in the 
northern hemisphere, over twenty times in the last two million years.

NARRATOR: These events were so terrible that for years scientists 
wondered what had caused it, and could they ever threaten us again.

NARRATOR: In the search for answers they turned to the sun, our ultimate 
source of heat. They discovered that the pattern of ice ages matched 
strange wobbles in the earth’s orbit around the sun. These altered how 
the sun’s heat shone upon the earth. They allowed the ice to grow and 
retreat.

Prof RICHARD ALLEY (Penn State University): And these wiggles in earth’s 
orbit are very regular, they’re very predictable, they make sense and so 
there’s this long slow bumpy slide in to an ice age and then a climb out 
of an ice age.

NARRATOR: They found that the ice ages didn’t happen at random. They 
followed a slow and predictable pattern. It took ninety thousand years 
to grow an ice sheet and about ten thousand years to melt it. That 
predictability allowed scientists to calculate when the next one was 
due. It was reassuring news, not for thousands of years.

Prof RICHARD ALLEY: For a big ice age, a big climate change, we don’t 
expect anything to happen on human time scales of a few dozen generations.

NARRATOR: The message from the sun seemed to be clear. We had no reason 
to fear a massive drop in temperatures, at least that’s what 
conventional theory said.

NARRATOR: Then fifteen years ago Richard Alley came to Greenland to 
study how our climate had changed since the last ice age.

Prof RICHARD ALLEY: When we started working in Greenland we knew we were 
on to something big. We really expected that we were going to find 
things that might surprise us.

NARRATOR: Greenland is like an ancient thermometer, a unique record of 
what has happened to the weather. Every single year for the last a 
hundred thousand years. It’s all because the ice is preserved in layers, 
the further down you drill the older the snow.

Prof RICHARD ALLEY: If you took all these pieces of core that have been 
collected and put them end to end they’re about two miles long and this 
is a sort of two mile time machine.

NARRATOR: Each layer records what was happening in the earth’s 
atmosphere at the time the ice was formed. Whether it’s the traces of a 
huge natural disaster or pollution from human activity, it’s all frozen 
and perfectly preserved.

Prof RICHARD ALLEY: We can see this, this ice core is beautifully 
layered and we can ask of it what happened, what was coming through the 
atmosphere at that time. Is there ash and acids from a big volcano, is 
there lead from Roman lead refining or what have you? So there’s this 
history of what was blowing through the air and piling up on top of the 
Greenland ice sheet, sitting here on these beautiful layers.

NARRATOR: But the most important measurement preserved in the layers is 
the temperature. The ice that Ally brought back to the lab was in effect 
the annual weather reports since the beginning of the last ice age. What 
he was looking for was changes in the amount of so called heavy water 
held in the ice. The basic rule, the more heavy water the warmer the 
climate. If the conventional wisdom about climate change was true then 
when he plotted the results he would expect to see slow changes in heavy 
water as the world warmed and cooled during the last ice age. But that’s 
not what he found.

Prof RICHARD ALLEY: This flabbergasted us, I think this flabbergasted a 
lot of people.

NARRATOR: The changes were anything but slow. He saw that temperatures 
could drop suddenly and catastrophically. And it happened far more often 
than was predicted by the passage of ice ages.

Prof RICHARD ALLEY: The world sometimes did change in the slow grand 
sleeps and sometimes it changed like a light switch.

NARRATOR: The earth’s past was full of devastating climate jilts, none 
as bad as a full ice age but enough to turn Britain in to Alaska. The 
search was on to find out what could trigger these climatic disasters. 
They searched through the ice record for clues. Had huge volcanoes 
blotted out the sun? There was no evidence for that. A succession of 
asteroid impacts? Again, no evidence. More wobbles in the sun’s orbit? 
That didn’t fit. In fact no one could account for what Ally had 
discovered. Except for one man who thought he could. Wally Broecker is 
the guru of climate science. He was convinced that it was all to do with 
the oceans.

Prof WALLY BROECKER (Columbia University): I’m convinced that the ocean 
is at the core of the whole thing. The trigger lies in the ocean.

NARRATOR: Not everyone saw it his way.

Prof WALLY BROECKER: And of course you started out was three allies in a 
hundred people, who think it’s nuts.

NARRATOR: Broecker’s attention was drawn to one ocean current in 
particular, the gulf stream. Britain bathes in its heat. It begins south 
of the equator and as it flows along the gulf of Mexico it absorbs heat 
from the tropics. It continues on past the coast of Britain.

Prof WALLY BROECKER: It’s roughly equal to all the rain in the world. 
Fifteen million cubic meters per second.

NARRATOR: The current carries the heat of a million power stations. It 
means we can swim in the sea at the same latitudes that Canada has polar 
bears. But the most important thing about it happens further north. It 
sinks.

Prof WALLY BROECKER: When it gets up in to the northern regions of the 
Atlantic, cooled and make denser and it sinks in to the deep sea and 
goes back the other way.

NARRATOR: This sinking is caused by salt in the water. When the salty 
water cools near Greenland it becomes so dense that it plummets to the 
bottom of the ocean. The water then heads back south to where the gulf 
stream began, and the whole process begins again. It’s a continuously 
circulating belt of water and heat, that’s why it’s called the conveyor. 
The sinking off Greenland is vital, this is what keeps Britain forever 
warm. So Wally began to speculate what would happen if the conveyor 
ceased to flow. Could that explain those dramatic falls in temperature? 
Trouble was most scientists were convinced that the oceans never changed 
at all.

Prof WALLY BROECKER: People tended to think about it as something that 
went on and on and on and on. We assume that the properties of the ocean 
are at a steady state, but if it’s changing then you can't assume that 
anymore and it makes real chaos.

NARRATOR: Then came something that shocked everyone out of their 
complacency. Something so small it might have been completely 
overlooked. Lloyd Keigwin spends his time examining mud samples from the 
bottom of the ocean. Mud cores just like the ice in Greenland can tell 
the history of activity in the ocean and what was going on in the 
conveyor. In particular Keigwin was looking for tiny sea shells called 
forams. These lurk on the ocean floor feeding on nutrients that sink to 
the sea bed.

Dr LLOYD KEIGWIN (Woods Hole Oceanographic Inst.): The forams build 
their shells out of calcium carbonate like any sea shell you’d find on 
the beach. And when they take carbon and oxygen and other elements out 
of the water to make their shell the chemistry of their shell reflects 
the chemistry and the physical properties of the water.

NARRATOR: When the conveyor flows most of the nutrients get swept past 
the forams, and so their shells are usually poor in nutrients.

Dr LLOYD KEIGWIN: When the conveyor is on the deep water of the north 
Atlantic is continually being flushed out and there aren’t a lot of 
nutrients that have accumulated. But if the conveyor went in to an off 
mode or a reduced mode um more nutrients would accumulate.

NARRATOR: Keigwin developed a way of measuring how much nutrients the 
forams must have absorbed.

Dr LLOYD KEIGWIN: We add a little more liquid nitrogen here, and this 
trap will capture the carbon dioxide produced as this sample falls in 
the hot acid. And soon we’ll know was the conveyor circulation on or off 
at this particular time.

NARRATOR: To his surprise he found massive variations in the composition 
of the shells. In other words at times in the past the conveyor must 
have switched off. When this work was published Wally Broecker knew 
exactly what it meant. It was the clue he had been looking for.

Prof WALLY BROECKER: The greatest joy to a scientist is discovery. It’s 
almost as if nature is trying to prevent us from uncovering her secrets.

NARRATOR: So he put it all together. The huge drops in temperature seen 
in the Greenland ice, the shells that said the conveyor had been cut 
off, they had to be connected.

Prof WALLY BROECKER: Well it was, it was this merging two parts of my 
science, the understanding of the ocean and the understanding of the 
climate. It popped in to my head that one way you could do that would be 
by turning on and off the what’s now called the conveyor belt, the deep 
water formation in the north Atlantic. And so I got the idea well hell 
if you turned that on and off or up and down, that could make at least 
in Europe very large climate changes.

NARRATOR: Broecker believed this explained the massive jolts in 
temperature seen in Greenland, the conveyor had switched off.

STATION ANNOUNCEMENT: We can only apologise to passengers for the 
inconvenience caused and for the disruption to services this morning.

NARRATOR: And if it had happened before it could happen again. And if it 
did Britain would be plunged in to a bitterly cold climate. But then 
someone pointed out one obvious flaw in the theory. This isn’t the age 
of global cooling but of global warming. Eight of the ten warmest years 
on record fell in the last decade. Climate experts are predicting 
temperatures to rise faster than at any time since the last ice age.

Dr RICHARD WOOD (Met. Office): The models that are used to make the 
predictions of global warming suggest that by the end of the century the 
warming we would see will be between about one and a half degrees and 
around six degrees. And really to go to see that in historical context 
you’d have to go back hundreds of thousands, maybe even millions of 
years to see a climate in the past that was that warm.

NARRATOR: The effects of global warming are being felt across the 
planet. The talk is not of ice but about how to prepare for hotter 
weather and the extremes that would bring.

PROF BILL MCGUIRE: Global warming should make the UK a more hazardous 
place to live. Particularly during the winter when we have not only more 
rain but we have more heavy precipitation, bursts of extreme rainfall. 
This is going to mean that for example river flooding is much more 
common, much more frequent and its implications will be much more serious.

Dr RICHARD WOOD: They’ll be changes in er frequency of things like 
tropical cyclones. And possible storms in the er outside the tropics and 
there are some latitudes to the UK and Europe.

NARRATOR: These are the changes our government is urgently planning for 
in the coming century. But recent discoveries suggest we might have to 
gear up for ice, not heat and rain. But our understanding of global 
warming maybe too simplistic. One of the most important of these 
discoveries was made by a team of NASA scientists based inside the 
arctic circle. Bill Krabill and his team have spent the last decade 
monitoring the effect of global warming upon the vast Greenland ice sheet.

BILL KRABILL (NASA, Wallops Island): This particular area, you can think 
of it as a huge ice cube that nicely offers global climate, an ice cube 
that’s a thousand miles long, four hundred miles wide and two miles 
thick in the centre.

NARRATOR: For years accurate measurements of the effects of global 
warming across the ice sheet were impossible. It was just too huge and 
inhospitable to measure from the ground. So they took to the air. 
Greenland is one of the biggest blocks of frozen water in the world. And 
if it started to melt the effects would be felt worldwide.

BOB THOMAS (NASA, Wallops Island): It comprises enough water to raise 
sea level by about six or seven metres if it all were to melt.

NARRATOR: They mapped the ice with a combination of global positioning 
satellites and lasers. The satellite measures the height of the plane 
and the laser measures the distance from the plane to the ice.

BILL KRABILL: There are five thousand individual beams per second that 
are being projected in to that scan there and then down in a pattern on 
the surface, measures the surface at ten centimetre accuracy.

NARRATOR: At five year intervals they have flown the same route across 
the island, each time they have measured the height of the ice. By 
comparing the two measurements they can see if the ice is growing or 
shrinking.

BILL KRABILL : There’s definitely changes taking place here, all over 
the margin of the Greenland ice sheet it is thinning. It’s equivalent to 
fifty cubic kilometres of ice and snow that are disappearing off the 
Greenland ice sheet each year.

NARRATOR: This fifty gigotonnes of water melting from Greenland was the 
first evidence that global warming might be effecting the ice sheet 
here. But one change really shocked them. They started to measure one of 
the island’s biggest glaciers.

BOB THOMAS: Less than ten years ago, five years ago, it was moving at 
about six, seven kilometres per year. And that was more or less in 
balance with the snowfall. Now in the five years since then the speed is 
almost doubled.

NARRATOR: It’s now advancing at twelve kilometres a year. The increase 
seems to be linked to global warming. It’s the fastest moving glacier on 
the planet. It dumps enough fresh water in to the sea each day to supply 
London for several months. Global warming seems to be reshaping the 
whole landscape of one of the biggest ice sheets on earth.

BOB THOMAS: Well I myself am convinced that global warming has affected 
the dynamics of the Greenland ice sheet and um that is possibly because 
increased melt water is creeping to the bed through crevasses and 
boullans and lubricating the bed and making it far more easy for the er, 
for the ice to flow.

NARRATOR: NASA have recently doubled their estimates of how much fresh 
water is coming off Greenland. To a hundred cubic kilometres per year. 
And much of that fresh water is flowing towards the sinking zone of the 
conveyor. Scientists began to wonder just what could be the effect of 
all that fresh water on the conveyor. They began to realise that because 
the conveyor was driven by the salty water sinking then too much fresh 
water would dilute the salt and so if the salt was diluted too much the 
conveyor wouldn’t sink.

Dr TERRY JOYCE (Woods Hole Oceanographic Inst.): What’s amazing about 
this is that how well fine tuned the system is. Where only a one percent 
chance in the salinities maybe significant, may tip us over in to this 
regime where the water is too fresh at higher altitudes to sink and the 
conveyor will stop.

NARRATOR: Cut off the conveyor and a climate catastrophe would happen. 
The only question was just how much fresh water would it take. The truth 
is that no one quite knows. What they do know is that Greenland isn’t 
the half of it. There is another even bigger source of fresh water 
heading straight for the sinking zone. Predictions are that global 
warming will lead to a much wetter world, because warm air can hold more 
moisture. And when it heads north and cools it should lead to more rain. 
In 2000 a team of American scientists travelled to Siberia. They studied 
the effects of global warming on some of the biggest rivers in the world.

Dr BRUCE PETERSON (MBL, Woods Hole): If you took the Ob, the Enesai and 
the Elena rivers and put them side by side you’d have a volume of 
discharge equivalent to three Mississippi rivers.

NARRATOR: The rivers collect rain that has fallen over a vast area of 
land. They already carry nearly twenty times the amount of fresh water 
towards the sinking zone, then drains from the ice in Greenland. 
Peterson wanted to find out if global warming had led to more water in 
these rivers. The warming in the last hundred years is only about half a 
degree. He measured how the flow of water had changed.

Dr BRUCE PETERSON: An increase in annual discharge of a hundred and 
twenty eight cubic kilometres per year. You probably can not imagine 
what a hundred and twenty eight cubic kilometres per year’s like. It’s a 
large volume of water.

NARRATOR: And in the coming century we’re expecting up to ten times more 
global warming. So Peterson decided to calculate how much more fresh 
water that could bring.

Dr BRUCE PETERSON: At the end of the next hundred years we expect 
approximately fifty percent increase in the discharge that these rivers 
would occur.

NARRATOR: It’s a horrifying prospect. A fifty percent increase in some 
of the world’s biggest rivers. If Peterson’s projections are true a vast 
wall of fresh water will soon come flooding through northern Siberia. An 
extra thousand cubic kilometres a year more could flow in to the salty 
waters of the conveyor. The impact could be immense. And that was the 
warning that Bill Turrell had seen in the deep. He’s been monitoring the 
saltiness of the conveyor as it flows past the Faro Isles north of Scotland.

DR BILL TURRELL: This is the device we use to measure the salinity in 
the ocean. These bottles here collect the water samples that we bring 
back to the ship to analyse, to collaborate the electronics which are 
down here. This package measures temperature, salinity, about twenty 
five times a second as we lower it down from the surface down to the seabed.

NARRATOR: If the saltiness of the water is dropping it’s a sign that the 
driving force of the conveyor is weakening.

DR BILL TURRELL: This graph shows the salinity or saltiness of the 
bottom water. It’s the saltiness from 1900 to the present day.

NARRATOR: Until the 1970s the salinity had been almost constant. But 
then it began to drop.

DR BILL TURRELL: After the late seventies we began to see a freshening 
of the bottom water. So much so that we, we began to doubt our own 
results. We took further samples, we checked with other countries who 
are sampling the same water, until eventually we became convinced that 
this change was actually happening.

NARRATOR: Turrell had measured the largest and most dramatic change 
recorded in the era of modern instruments. And there was worse. He took 
measurements from the very bottom of the ocean, from the return leg of 
the conveyor. Its flow had fallen by a massive twenty percent.

DR BILL TURRELL: It’s the first changes that we’d expect to see if we 
thought that global warming was beginning to effect the conveyor belt. 
Er a few years ago I probably wouldn’t have said that because global 
warming was far more iffy, it wasn’t so significant, it wasn’t so 
certain. Now we really do know that fresh water input to the Arctic is 
increasing. The Siberian rivers are pumping out more fresh water. The 
Arctic ice sheets are melting and there is more release of fresh water. 
It, it’s the most fundamental change I’ve observed in my career.

NARRATOR: The process that could cut off the conveyor has begun. We 
don’t know where the cut off point is, we just know we’re getting closer 
to it.

Prof RICHARD ALLEY: I don’t think that an abrupt sudden trip and fall 
down the stairs is the most likely outcome. But I think that the 
probability of that is high enough that we should really think about it.

Dr TERRY JOYCE : The likelihood of having an abrupt change is increasing 
because of global warming is moving us closer and closer to the brink. 
We don’t know where that is but we know one thing, we’re moving towards 
the edge. And so I would say within the next hundred years it’s very 
likely. In other words a fifty percent probability that this might happen.

NARRATOR: So there could be a fifty percent probability that the 
conveyor will stop flowing past the shores of Britain. Perhaps a one in 
two chance that one of the most important sources of heat in the world 
will just disappear. What would happen to us if the heat of a million 
power stations were to cut off? The answer depends crucially on how soon 
it happens. The Met Office has run a series of possible scenarios. In 
the first they examined what would happen if the conveyor cut off in 
fifty years. They have balanced the effects of fifty years of global 
warming against the regional cooling caused by the conveyor cutting off. 
In this scenario the area around Britain does indeed get colder.

Dr RICHARD WOOD: Cooling due to the ocean circulation collapsed is even 
stronger than the global warming. We’re still looking at a climate which 
is a lot colder than today’s.

NARRATOR: But how much colder? This was the coldest winter in the past 
century. A freak event not easily forgotten.

PROF BILL MCGUIRE: The winter of 1962 to 1963 is something that people 
of my age particular remember because from Boxing day ‘til March there 
was very deep snow on the ground across much of England.

NARRATOR: Blizzards lashed the country for day after day. In places snow 
lay eight meters deep. And temperatures fell to minus twenty two degrees.

Dr RICHARD WOOD: That would have had a huge impact on, on people’s 
lives. There’s a lot of disruption to all sorts of infrastructure, 
people were snowed in for long periods, over quite a wide part of the 
country.

NARRATOR: The electricity supply failed across the whole south east. 
Crops had to be drilled out of the ground. We asked the Met. Office to 
examine their scenario and calculate how often we could expect a winter 
like this. Their answer, once every seven years. But there is a second 
scenario the scientists have been examining.

PROF BILL MCGUIRE: Well I can only describe it as catastrophic.
BOB GASGOSIAN: The implications are huge.

PROF BILL MCGUIRE: It’s clearly going to influence every single one of 
us every day of our lives.

BOB GASGOSIAN: The economic implications, the political implications, er 
and the national security implications, for all countries.

NARRATOR: This scenario is that the gulf stream conveyor cuts off, not 
within fifty years but twenty. It’s described as a low probability, high 
impact event. The whole of north west Europe gets a lot colder.

Dr RICHARD WOOD: This is really a huge change in climate, a massive 
cooling. If this was to happen we would certainly have a future which 
was very cold, very different from what we have today.

NARRATOR: The coastline of Britain would become unrecognisable.

Dr RICHARD WOOD: You could expect to see er sea ice off the coast of, 
off the coast of south east England probably several miles off shore.

NARRATOR: We would struggle to keep our coastline open and our ports 
working. But the effects of a shutdown could be even greater on land. 
Winter blizzards would bring us entirely new hazards.

PROF BILL MCGUIRE: We’d expect to see ice storms. Now these are severe 
winds but they bring with them either frozen rain or snow which clogs up 
and builds up on cables, power cables, telephone cables, brings them 
down very effectively. These conditions can persist for days and can 
really bring a country to its knees.

NARRATOR: Our infrastructure would be in danger of collapse.

PROF BILL MCGUIRE: The power lines would ice up, they’d snap, they’d 
collapse and this could happen virtually country wide during the worst 
of these storms.

NARRATOR: With enough warning we could make plans and adapt to our new 
landscape. The trouble is there wouldn’t be any warning.

Dr TERRY JOYCE: It’ll be quick and suddenly one decade we’re warm, the 
next decade we’re in the coldest winter that we’ve experienced in the 
last hundred years, but we’re in it for a hundred years.

NARRATOR: Winters like this would be commonplace.

PROF BILL MCGUIRE: I think we’d be extraordinarily poorly equipped to 
deal with a gulf stream shutdown. If we’re dealing with a situation 
where snow is on the ground for perhaps thirty days a year or maybe up 
to a hundred days a year, with temperatures regularly down in the minus 
twenties, I think we’ll find it very, very difficult to cope with that.

NARRATOR: It could mark the end of the British way of life as we’ve 
known it. But there is something even more disturbing about the conveyor 
cutting off. Something that suggests it could cause a catastrophe of 
truly global proportions if it were to happen. The Met Office have run 
another computer simulation. It shows a clear link between a conveyor 
cut off and patterns of rainfall across the world.

Dr RICHARD WOOD: One thing that’s really surprised us was the fact that, 
that the impact is not just confined to our part of the world.

NARRATOR: The dark red areas of his map suffer massive drops in rainfall.

Dr RICHARD WOOD: The main rain band in the tropics would move quite a 
bit south so all these countries in the red region here would lose a 
very large proportion of their rainfall and that could impact on a large 
number of people in those parts of the world.

NARRATOR: Central America would be one of the worst hit regions. It 
could lose up to forty percent of its rainfall.

Dr RICHARD WOOD: The model suggests that the present er vegetation in 
the rainforest wouldn’t be sustainable in that situation, and the forest 
would die and be replaced by grassland.

NARRATOR: While we shivered through long and bitter winters huge tracks 
of forest would die away. Well that’s what the computer model said. And 
then came evidence that it had actually happened before. The clues came 
from within Richard Alley’s ice cores. They contained bubbles of ancient 
air, evidence of how the atmosphere has changed. Alley’s attention 
focussed on one gas that was present in the bubbles, methane. It’s 
produced naturally by bacteria in the tropics when they receive plenty 
of rainfall, and it disappears at times of drought.

Prof RICHARD ALLEY: And so you can ask of those bubbles how many swamps 
were there on earth. And this is wonderful because it tells you 
something that’s happening across a whole bunch of the land area. If the 
world dries up partially they’ll be much less methane in the air and it 
will show up, right there.

NARRATOR: He found that the methane levels plummeted at the same time as 
temperatures had dropped in the past. It seemed the conveyor cut off 
made the world drier.

Prof RICHARD ALLEY: And when the north Atlantic has been cold in the 
past the monsoon seems to have weakened or failed in places in Asia. 
Chill out the northern Europe and you dry a lot of places around a lot 
of millions of people with that.

NARRATOR: The monsoon is a lifeline to hundreds of millions of people 
living across the Asian subcontinent. Agriculture depends on its heavy 
rains. Should this scenario ever happen it would bring disaster on an 
unimaginable scale. There would be famine, economic collapse and 
refugees on the move.

DR BOB GASGOSIAN: We had only three billion people on this earth in 
1962, we have over six billion now. Where are these people going to go 
if there are economic hard times? If we were to get on the same scale of 
the Irish famine today, that occurred then, I am very concerned at what 
would happen at that time.

NARRATOR: And there is a final twist to these scenarios. Switching the 
conveyor off can happen at speed. But switching it back on is altogether 
harder.

TERRY JOYCE: We’re moving along and suddenly we drop down, how do we 
switch it back on? Well we would have to climb this cliff. There’s an 
enormous amount of energy required to climb that cliff.

Prof WALLY BROECKER: And there’d be nothing in the meantime we could do 
to change it.

TERRY JOYCE: We have to reveres this effect of global warming by 
hundreds of years.

NARRATOR: We are now preparing for more heat and more rain. But our new 
understanding of how climate change works challenges all that. It 
suggests our defences could be pointing the wrong way.
"

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