Science News
Last 100 years warmest since 9th century, say British researchers
By DPA
Feb 10, 2006, 12:51 GMT

London - Findings by British scientists support earlier evidence that climate change has contributed to the warmest temperatures in the northern hemisphere since the 9th century, research published Friday showed.

Researchers at the University of East Anglia (UEA) in eastern Britain, measured changes in fossil shells, tree rings, ice cores and other past temperature records or 'proxies' to reach their findings, which were published in the journal Science Friday.

They also looked at people's diaries from the last 750 years.

Timothy Osborn and Keith Briffa of UEA analysed instrument measurements of temperature from 1856 onwards to establish the geographic extent of recent warming.

Then they compared this data with evidence dating back as far as 800 AD.

The analysis confirmed periods of significant warmth in the northern hemisphere from about 890 to 1170 AD - the so-called Medieval Warm Period - and for much colder periods from about 1580 - 1850, known as the Little Ice Age.

The UEA team showed that the present warm period is the most widespread temperature anomaly of any kind since the 9th century.

The scientists used 14 sets of temperature records from different locations across the northern hemisphere.

The records included long life evergreen trees growing in Scandinavia, Siberia and the Rocky Mountains which had been cored to reveal the patterns of wide and narrow tree rings over time. Wider rings related to warmer temperatures.

The chemical composition of ice from cores drilled in the Greenland ice sheets revealed which years were warmer than others.

Finally, the researchers used proxy data developed from the diaries of people living in the Netherlands and Belgium during the past 750 years that revealed, for example, the years when the canals froze.

'These records extend over many centuries and even thousands of years. We simply counted how many of those records indicated that, in any one year, temperatures were warmer than average for the region they came from,' said Osborn.