Late 20thC was warmest in 1400 years

New climate records show Earth was warmer in the late 20th century than in the previous 1400 years. Source: AAP

EARTH was cooling until the end of the 19th century and a hundred years later the planet's surface was on average warmer than at any time in the previous 1400 years, according to climate records.

In a study spanning two millennia published in Nature Geoscience, scientists say a "long-term cooling trend" around the world swung into reverse in the late 19th century.

In the 20th century, the average global temperature was 0.4C higher than that of the previous 500 years, with only Antarctica bucking the trend.

From 1971-2000, the planet was warmer than at any other time in nearly 1400 years.

This measure is a global average, and some regions did experience warmer periods than that - but only for a time. Europe, for instance, was probably warmer in the first century AD than at the end of the 20th century.

The investigation is the first attempt to reconstruct temperatures over the past 2000 years for individual continents.

It seeks to shed light on a fiercely contested aspect in the global warming debate.

Sceptics have claimed bouts of cooling or warming before the Industrial Revolution - including two episodes in Europe called the Medieval Warm Period and the Little Ice Age - are proof that climate variations are natural, not man-made.

The new study does not wade into the debate about greenhouse gases, but points to two planetary trends.

The first is a clear, prolonged period of cooling. It may have been caused by a combination of factors, including an increase in volcanic activity, with stratospheric ashes reflecting the sunlight, or a decrease in solar activity or tiny changes in Earth's orbit, both of which would diminish sunlight falling on the planet.

The cooling - between 0.1-0.3C per thousand years, depending on the region - went into reverse towards the end of the 19th century, and was followed by an intensifying period of warming in the 20th, the paper said.

Previous research into climate change has pointed to a warming spurt in the 20th century and attributed it to the rise of heat-trapping carbon gases emitted by burning coal, oil and gas.

The warming trend shifted up a gear in the middle of the 1970s, in line with record-breaking levels of carbon dioxide (CO2), according to this past research.

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