20th century warmer than any other time in nearly 1400 years

A major scientific research project has found that warming over the 20th century produced the hottest global average temperatures in 1400 years.

Using proxy records such as tree-ring measurements, pollen sampling, coral reefs, ice cores and historical records, an international team of scientists reconstructed temperatures over the past 2000 years.

The study, published in the journal Nature Geoscience, found that the global warming that began in the late-19th century reversed a long cooling trend across the planet that lasted well over 1000 years, the Sydney Herald reported.

“The striking feature about the sudden rise in 20th century global average temperature is that it comes after an overall cooling trend that lasted more than a millennium,” Dr Steven Phipps from the University of NSW's ARC Centre of Excellence for Climate System Science, one of the authors of the paper, said.

When the reconstructed temperatures are averaged across the planet, the best estimate of past temperatures finds 1971–2000 was warmer than any other time in nearly 1400 years.

But some of the seven different regions studied may have experienced similar or warmer temperatures at other times.

The researchers said the findings do not consider uncertainty associated with the temperature estimates, and the reconstruction for each area covered different periods within the 2000 years, depending on the availability of data.

In Australia and Asia, the reconstructed temperature was highest during 1971–2000 than at any other period over the studied timelines.

Professor Jonathan Overpeck, visiting fellow of the Victorian Centre for Climate Change Adaptation Research, said it confirmed that recent global and continental-scale warming was “very unusual” in recent Earth history and was driven mostly by human emissions of greenhouse gases.