Sat, 05 Jul 2003

Climate change: Not clear on the concept

Gwynne Dyer, Columnist, London

The World Meteorological Organization normally produces statistics-heavy reports at the end of the year, not news bulletins about today's weather. Its announcement on July 2 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 analyzed 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 realized 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 civilization, 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.