Warning of repeat of historic climate catastrophe

A SUDDEN and catastrophic change happened to the Earth’s climate about 5,000 years ago and history could be repeating itself today, scientists have warned.

New research suggests that the "monumental" change would have had a major impact on emerging cultures at the time.

The scientists behind the evidence, from Ohio State University, in the United States, warn that the lesson from the past is to beware of "tweaking" the planet’s finely tuned climate system, which can have drastic consequences.

Data from sources ranging from ancient frozen plants to ice core records and pollen deposits suggest a sudden drop in temperature 5,200 years ago, followed by a brief surge.

The most likely explanation is a huge solar oscillation which caused the Sun’s energy output to fall precipitously and then flare up. This had a devastating impact on Earth, the research suggests.

Professor Lonnie Thompson, who led the study, presented yesterday at a meeting of the American Geophysical Union in San Francisco, said: "Something happened back at this time and it was monumental. But it didn’t seem monumental to humans then because there were only approximately 250 million people occupying the planet, compared to the 6.4 billion we now have.

"The evidence clearly points back to this point in history and to some event that occurred. It also points to similar changes occurring in today’s climate. To me, these are things we really need to be concerned about."

One finding supporting the theory was the discovery of perfectly preserved plants that emerged from a massive retreating glacier in the Peruvian Andes. Carbon dating showed that the plants had been buried in ice for about 5,200 years. The climate had to have shifted suddenly and severely at this time for the ice to capture the plants.

The preserved body of a man who died and became trapped in ice at about the same time had also been found in an Alpine glacier.

Further evidence had emerged from a study of tree rings from Ireland and England spanning a period of 7,000 years. The point in that record when the tree rings were narrowest - suggesting the driest period experienced by the trees - was about 5,200 years ago.

In addition, ice cores from the summit of Mount Kilimanjaro in Africa contained oxygen isotopes bearing the signature of dramatically low atmospheric temperatures during the same critical period.

Scientists know that a historic global cooling called the Little Ice Age, which lasted from 1450 to 1850 AD, coincided with two periods of decreased solar activity. Professor Thompson believes the evidence from 5,000 years ago reflected a more catastrophic "blip" in the Sun’s energy output. He warned: "The climate system is remarkably sensitive to natural variability. It’s likely that it is equally sensitive to effects brought on by human activity, changes like increased greenhouse gases, altered land-use policies and fossil-fuel dependence.

"Any prudent person would agree that we don’t yet understand the complexities of the climate system and, since we don’t, we should be extremely cautious in how much we ‘tweak’ the system. The evidence is clear that a major climate change is under way."