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Climate Change Two

14 August 2003

What They Don’t Mention About Climate Change

By Gwynne Dyer

On several days last week, it was hotter in London than in Cairo. France has just declared a national emergency because of the extreme heat. But the winemakers of Germany are ecstatic about this year’s vintage, and Asian manufacturers of compact air-conditioning systems are having a boom year for European sales.

That’s how most people see climate change: a gradual warming-up that will hurt some people and benefit others. The people of Tuvalu and quite a lot of the Netherlands will be severely inconveniences as rising sea levels cover their homes, but they will either move or learn to breathe underwater. So no rush, no panic, and don’t take any measures that might hurt economic growth.

But anyone who has been paying attention to the evidence coming out of the Greenland ice cores for the past twenty years should know that the real threat is not gradual warming. It is that the warming will trigger an abrupt and rapid cooling of the global climate, with catastrophic consequences for existing human populations. And the Europeans would be hit first and worst, for the mechanism that would cause this shift is the disappearance of the Gulf Stream.

People talk about the ‘last ice age’ as if it were over, but it’s not. The current cycle of global glaciation began around three million years ago, when the land that is now Panama rose above sea level, closing the old ocean channel between North and South America and forcing a major reorganisation of ocean currents. Since then, ice sheets have covered around 30 percent of the land surface of the planet most of the time, although this has been regularly interrupted by major melt-offs called ‘inter-glacials’ when the ice coverage drops to about 10 percent.

During the past million years these warm, wet episodes have come along approximately every 100,000 years. The present inter-glacial began about 15,000 years ago, and nobody knows for sure how long it will last. We do know, however, that the previous inter-glacial began about 130,000 BC, and lasted for 13,000 years — so we could already be in overtime on this one.

The good news is that we don’t automatically slide back into maximum glaciation. What happened in 113,000 BC was that the global climate flipped into a cool, dry, windy phase that was much less pleasant than our current balmy conditions: average temperature at least 5 degrees C (9 degrees F) lower than the present, and massive droughts all over the place. It took a further push — probably massive volcanic eruptions in Indonesia around 70,000 BC — to start the ice sheets growing again.

The bad news is that even the ‘cool, dry, windy’ phase of the global climate would wreck human civilisation. The whole enterprise of civilisation that has allowed the human population to grow from perhaps 10 million to over 6,000 million has occurred within the warm, wet climatic bubble of the past ten thousand years. At least half the lands that now support agriculture would revert to tundra or semi-desert if we flipped back to the cool, dry and windy climate, and billions would die in the chaos of war and starvation that would follow.

Now for the worse news. When the flip happens, it isn’t gradual at all. The Greenland ice cores, a quarter-million-year record of annual snowfall that also tells us about average temperature, precipitation and even wind speed, contain an alarming message. When the climate mode shifts, global temperatures crash in 10 years or less — and stay down for centuries or millennia. And the very worst news is that the sudden flip into cool-and-dry is caused by gradual global WARMING.

The key to the whole cycle seems to be the Gulf Stream, which normally delivers huge amounts of warmth to the northern North Atlantic and western Europe (which would otherwise have the climate of Labrador). But ocean currents are basically conveyor belts for moving salt around the world’s oceans. If the warm water of the Gulf Stream, made even more dense and saline by evaporation on its long journey north, does not sink to the bottom and flow back south when it reaches the Greenland-Iceland-Norway gap, then the whole conveyor belt shuts down.

What stops the salty water from sinking? Dilution by too much fresh water on the surface, coming either from increased rainfall over the North Atlantic or from glacial melting and sudden outflows of fresh water from the Greenland fjords. What might cause these events? A rise in temperature in the region — and while average global temperature has only risen about one degree in the past century, the rise in the Arctic region has been several times greater.

The evidence in the Greenland ice cores is clear: the abrupt, high-speed flips in global climate known as Dansgaard-Oeschger events have happened many dozens of times. Maybe if we have a couple of more centuries of warm-and-wet conditions, we will learn enough about the fine detail of global climate to postpone the next flip indefinitely. But if it goes over the edge now, it’s a calamity for everybody.

Europeans, whose agriculture could no longer feed even a tenth of their current population, would be hit hardest of all, though nobody would get away with less than a fifty percent loss. So why didn’t this prospect get more media attention during the recent unprecedented heat wave in Europe? Maybe all the science journalists were on vacation.


To shorten to 725 words, omit paragraphs 9 and 10. (“The key…greater”)

Climate Change: Not Clear on the Concept

3 July 2003

Climate Change: Not Clear on the Concept

By Gwynne Dyer

The World Meteorological Organisation normally produces statistics-heavy reports at the end of the year, not news bulletins about today’s weather. Its announcement on 2 July that the record extremes in weather being experienced globally this year are evidence that climate change is actually underway is therefore much more than just another salvo in the long argument about global warming.

In Geneva, where the WMO is based, daytime temperatures have not fallen below 25C (77F) since late May — the hottest June in at least 250 years. In the United States, May brought a record of 562 tornadoes (the previous record for one month was 399). In India, the pre-monsoon heat-wave brought peak temperatures of 45C (113F) and directly caused at least 1,400 deaths. As the WMO statement cautiously observed: “New record extreme events occur everywhere somewhere in the globe, but in recent years the number of such extremes has been increasing.” But there is still no sense of urgency, and hardly anybody addresses the real context of this change.

Two weeks ago, for example, the Bush White House censored a government report issued by the Environmental Protection Agency that analysed global warming and its sources. It eliminated any suggestion that human activities, notably industrial and vehicle emissions, were at least partly responsible for climate change. It removed references to a widely accepted 1999 study showing how sharply temperatures had risen in the previous decade compared with the 1,000-year pattern, and substituted a controversial later study, partly financed by the oil industry, that disputes the evidence. The green lobby complained, and the media covered the story in a desultory way, but everyone continued to behave as though there was lots of time.

The problem is that ‘global warming’ was the first aspect of climate change to catch the public’s attention, and for the vast majority of people it remains the only threat — if indeed it is a threat. After all, warmer isn’t necessarily worse, and anyway it’s a gradual process and we’ll all probably be safely dead before it gets too serious. Climate researchers have known that this is untrue for about twenty years, since the evidence of the Greenland ice-cores became available, but it has still not affected the public debate.

Those cores go down two miles (three km.) into the Greenland ice-cap and bring up year-by-year evidence of weather that goes back a quarter-million years. What the shocked researchers realised when they examined the cores is that climate change — REAL climate change — is not gradual at all. It’s a threshold phenomenon, a sudden flip into a radically different state that may then persist for a very long time. The real danger we face is that gradual warming of the sort we are experiencing now will trigger a sudden cooling that could drop average global temperatures by 5C (9F) in ten years.

The sudden cooling and the accompanying droughts would destroy most of the agriculture that now sustains six billion of us, and at least 90 percent of the human race would be killed by famine and war in a matter of a decade or so. These abrupt climate changes can herald the beginning of the next Ice Age, but climatic flips like this can also occur for lengthy periods even in the midst of warm-and-wet interglacial periods like the present.

We do still live in the Ice Ages, of course. For the past three million years, ever since continental drift closed the channel between North America to South America and changed the ocean currents, glaciers have covered over a third of the planet’s surface almost 90 percent of the time. The recent pattern has been around 100,000 years of freeze followed by a much shorter warm period. The previous interglacial, which ended 117,000 years ago, was only 13,000 years long, so at 15,000 years we’re already into overtime on this one — but we don’t even need a major Ice Age to do the damage.

The process by which the climate flips is now fairly well understood. The trigger is a phase of gradual warming that, either through glacial melting or just more rainfall, increases the amount of fresh water on the ocean surface between Labrador, Greenland and Norway. This critical part of the North Atlantic is where the Gulf Stream’s water, having become salty and dense through evaporation, sinks to the bottom and flows back south — but if it is diluted by too much fresh water on the surface, it doesn’t sink and the circuit is broken.

The whole global climate suddenly flips into a cool, dry phase that can last for many centuries before warmer conditions return: there have been two such episodes, at 12,500 years ago and 8,500 years ago, even since the end of the last Ice Age. Or the cool, dry phase could last for a hundred thousand years if other conditions, like the shape of the earth’s orbit and the tilt of its axis, have already put us on the brink of a new Ice Age.

The flips of the past were caused by natural warming of one kind or another, but by adding man-made warming to the problem we are making it far more dangerous. We have built all of human civilisation, and increased our population a thousandfold, since the last cool, dry episode. All of that is at risk if the climate flips, and yet the public debate is still all about gradual change.


To shorten to 725 words, omit paragraphs 3 and 7. (“Ten…time”; and”We…damage”)