Climate change: Current warming 'unparalleled' in 2,000 years

The speed and extent of current global warming exceeds any similar event in the past 2,000 years, researchers say.

They show that famous historic events like the "Little Ice Age" don't compare with the scale of warming seen over the last century.

The research suggests that the current warming rate is higher than any observed previously.

The scientists say it shows many of the arguments used by climate sceptics are no longer valid.

 The events were seen by some as evidence that the world has warmed and cooled many times over the centuries and that the warming seen in the world since the industrial revolution was part of that pattern and therefore nothing to be alarmed about.

Three new research papers show that argument is on shaky ground.

The science teams reconstructed the climate conditions that existed over the past 2,000 years using 700 proxy records of temperature changes, including tree rings, corals and lake sediments. They determined that none of these climate events occurred on a global scale.

The "Medieval Warm Period", which ran between AD 950 and AD 1250 only saw significant temperature rises across 40% of the Earth's surface.

Today's warming, by contrast, impacts the vast majority of the world.

"We find that the warmest period of the past two millennia occurred during the 20th Century for more than 98% of the globe," one of the papers states.

"This provides strong evidence that anthropogenic (human induced) global warming is not only unparalleled in terms of absolute temperatures but also unprecedented in spatial consistency within the context of the past 2,000 years."

What the researchers saw is that prior to the modern industrial era, the most significant influence on climate was volcanoes. They found no indication that variations in the Sun's radiation impacted mean global temperatures.

The current period, say the authors, significantly exceeds natural variability.

"We do not focus on looking at what's causing the most recent warming as this has been done many times and the evidence is always agreeing that it is the anthropogenic cause," said researchers.

"We do not explicitly test this; we can only show that natural causes are not sufficient from our data to actually cause the spatial pattern and the warming rate that we are observing now."

Other scientists have been impressed with the quality of the new studies.

 

Lara Khouli

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