Humanity may not be to blame for global warming after all

Published on Monday 12 May 2003 01:00

LAST week, the European Environment Agency revealed that the EU was lagging, quite significantly, in achieving its targets for reducing emissions of greenhouse gases under the Kyoto Protocol, because of a particularly cold winter, which required consumers to use more energy.

Based on a sense of dread, Europeans have been led to believe that drastic measures such as Kyoto are necessary to prevent the risk of negative outcomes from a changing climate. Unfortunately, it is more likely that resources are being misallocated to a problem which is not vetted in scientific facts.

Thermometers across the world have recorded a globally-averaged surface warming trend of approximately 0.6C during the 20th century, although much of that trend occurred early in the century, before the major increase in human-caused emissions.

A drawback of the globally-averaged surface temperature record obtained from thermometers is its brevity - the record begins in the mid-19th century. The climate change debate has been fuelled by the misconception that the 19th century is "normal" and that the late 20th century warming trend (about 0.1C per decade) is unusually strong. However, the earth’s climate changes naturally, and this is the backdrop against which the influence of human beings must be judged.

The UK has one of the longest-running instrumental measurements of temperature: the Central England Temperature Record, which started in 1659 and encompasses roughly the area of London, Bristol and Preston. That shows a gradual and natural warming trend of 0.8C over the past 300 years, 200 years before the increase in greenhouse gases.

To go back further, teams of researchers have mined ecological reservoirs that hold information on past climate change. These include glaciers, tree growth, coral growth, sea floor sediment, boreholes, ice sheet cores, insects, pollen, stalactites and stalagmites, as well as documentary records. Nearly all yield historical information on local climate.

A recent review of more than 240 scientific articles using this proxy data by a team from Harvard University shows that the climate in most locations was not extreme or unusual during the 20th century. The warmest, or most extreme, climate occurred in the Medieval Warm Period, between the 9th and 14th centuries.

HH Lamb, the founder of the climatic research unit at East Anglia University, studied how climate influenced human affairs. He found that during the 12th and 13th centuries, England's climate was warm enough to support more than 50 vineyards, signifying that May frosts were rare. More than ten vineyards flourished for more than 100 years. About 1150 AD, William of Malmesbury noted in De Pontificibus: "No county in England has so many or so good vineyards as this Gloucester."

But this was short-lived. A cooling period known as the Little Ice Age began by 1300, and it persisted in some regions until 1900. Western Europe experienced more frequent acute winters, early frosts and more climate variability from year to year. The Little Ice Age intensified from about 1550 to 1700. All seasons experienced low temperatures on average, accompanied by high variability from year to year. Extreme storms occurred in the North Sea and central Europe, with the 1690s being perhaps the most severe decade. During 1693- 1700, Scotland suffered its worst famine when crops failed for seven out of eight years.

By the 19th century, the Little Ice Age had largely abated. To some extent, early 20th century warmth can be seen as a natural recovery from the harsh cold of previous centuries, and the 20th century is neither extreme nor unusual compared to the last 1,000 years. Little firm knowledge exists to explain the broad climate extremes of the last millennium, making forecasts of future climate highly uncertain.

The scientific data from the past millennium suggest a context for the debate about climate change - namely, that a trend of human-induced warming does not exist. Politicians and interest groups are keen to scare the public into believing that they are the cause of a warming climate, and that costly policies are necessary to mitigate the risks. The debate needs scientific facts - not psychological instincts - to inform its course of action.

Dr Baliunas is an astrophysicist at the Harvard-Smithsonian Centre for Astrophysics.