News / Science & Technology

Scientists Reconstruct 2,000 Years of Temperature Change

Climate scientist studies ice core from Antarctica. (T. Bauska)
Climate scientist studies ice core from Antarctica. (T. Bauska)
Rick Pantaleo
A team of 78 researchers from around the world published a study on Monday detailing what they call the most comprehensive reconstruction of temperature changes on every continent for the last two millennia.

The research, outlined in the online edition of the journal Nature Geoscience, said there had been an overall cooling trend across nearly all the world’s continents during the last 1,000 to 2,000 years. But that trend came to a halt in much of the world near the end of the 19th century, the study concluded, adding that the period between 1971 and 2000 was the warmest in 1,400 years.

The researchers, coordinated by the Past Global Changes (PAGES) project based in Switzerland, were able to make their conclusions by combining data from records that were taken from sources such as tree rings, pollen, corals, lake and marine sediments, ice cores, stalagmites and assorted historical documents taken from 511 locations throughout Earth’s seven continents.

The researchers said they expect their expansive new dataset will be used in future studies, including comparisons with the output of climate models used to help project future climate change.
 
Noting that climate records from Africa remain sparse, lead study author Darrell Kaufman, a professor at Northern Arizona University in Flagstaff, said, “There were too few records to accurately determine long-term temperature changes for that continent.”

The scientists noted that variations in temperatures across the continents were much more alike within their own hemispheres than between the Northern and Southern Hemisphere.

"Distinctive periods, such as the Medieval Warm Period or the Little Ice Age stand out, but do not show a globally uniform pattern on multi-decadal time scales," says co-author Professor Heinz Wanner of the University of Bern.

The Frozen Thames River 1677. (Painting by Abraham Hondius via Wikimedia Commons)The Frozen Thames River 1677. (Painting by Abraham Hondius via Wikimedia Commons)
x
The Frozen Thames River 1677. (Painting by Abraham Hondius via Wikimedia Commons)
The Frozen Thames River 1677. (Painting by Abraham Hondius via Wikimedia Commons)
The cooling trend was felt throughout the world by approximately 1500 AD when temperatures fell below the long-term mean nearly everywhere.  However, the researchers noted, this drop in mean temperature took place centuries earlier in the Arctic, Europe and Asia than it did in North America and the Southern Hemisphere.

“These new findings will certainly stimulate vibrant discussions within the research community,” says Professor Wanner.
 
The researchers said the most common feature they found throughout the regions of the world was a long-term cooling trend.  The study suggests that a combination of factors such as an increased global volcanic activity, decreased solar activity, changes in land cover, and slow changes to Earth’s orbit all contributed to the cooling trend.

The warming that began in the late 19th to early 20th century was twice as much, on average, in the northern regions of the world as it was in the Southern Hemisphere.
Antarctica has been the only continent so far to buck the warming trend.  

The researchers analyzed the average temperatures over 30-year periods and found that the period from 1971 to 2000 was most likely warmer overall than any other 30-year period over the last 1,400 years.

But looking back further, the researchers found that there were some areas that experienced even warmer 30-year intervals than the 1971 to 2000 period.  Europe during the Roman Empire, for example, was most likely warmer between 21 and 80 AD.
 
Britain's 13th century Berrow Church in the Bristol Channel region was once inundated by sand dunes during the so-called Medieval Warm Period.Britain's 13th century Berrow Church in the Bristol Channel region was once inundated by sand dunes during the so-called Medieval Warm Period.
x
Britain's 13th century Berrow Church in the Bristol Channel region was once inundated by sand dunes during the so-called Medieval Warm Period.
Britain's 13th century Berrow Church in the Bristol Channel region was once inundated by sand dunes during the so-called Medieval Warm Period.
Weaker solar activity and an increase in tropical volcanic eruptions, on the other hand, may have produced some intensely cooler 30-year periods between 830 and 1910 AD.  The researchers noted that both weakened solar activity and increased volcanic activity often took place at the same time which they say led to a drop in the average temperature during five distinct 30 to 90-year intervals between 1251 and 1820.

“Previous attempts to reconstruct temperature changes focused on hemispheric or global-scale averages, which are important, but overlook the pronounced regional-scale differences that occur along with global changes,” said Professor Kaufman.  "A key aspect of the consortium effort was to engage regional experts who are intimately familiar with the evidence for past climate changes within their regions," he added.

"Several mathematical procedures were applied to reconstruct the continental temperature time series and they were compared to assess the extent to which the main conclusions of the study stood up to the different analytical approaches."

This study along with other work performed by the “PAGES” project is funded primarily by Swiss and U.S. national science foundations.

You May Like

Photogallery Oxfam: Ebola Could Be 'Disaster of Our Generation'

Meanwhile, Fidel Castro, the former leader of Cuba, says the Caribbean island nation will 'gladly cooperate' with the US in the fight against Ebola in West Africa More

Multimedia Kobani Fighting Sends 400,000 Refugees to Turkey

Refugees receive help from Turkish authorities and individuals, but say much more is needed More

India’s Ruling Nationalist Party Makes Gains in Regional Elections

Bharatiya Janata Party’s huge margin over its rivals puts it on course to form governments in the northern Haryana and western Maharashtra states More

Featured Videos

Your JavaScript is turned off or you have an old version of Adobe's Flash Player. Get the latest Flash player.
Exclusive: American Joins Kurds' Anti-IS Fighti
X
Zana Omer
October 18, 2014 6:37 PM
The United States and other Western nations have expressed alarm about their citizens joining Islamic State forces in Syria and Iraq. In a rare counterpoint to the phenomenon, an American has taken up arms with the militants' Syrian Kurdish opponents. Elizabeth Arrott has more in this exclusive profile by VOA Kurdish reporter Zana Omer in Ras al Ayn, Syria.
Video

Video Exclusive: American Joins Kurds' Anti-IS Fight

The United States and other Western nations have expressed alarm about their citizens joining Islamic State forces in Syria and Iraq. In a rare counterpoint to the phenomenon, an American has taken up arms with the militants' Syrian Kurdish opponents. Elizabeth Arrott has more in this exclusive profile by VOA Kurdish reporter Zana Omer in Ras al Ayn, Syria.
Video

Video South Korea Confronts Violence Within Military Ranks

Every able-bodied South Korean male between 18 and 35 must serve for 21 to 36 months in the country’s armed forces, depending upon the specific branch. For many, service is a rite of passage to manhood. But there are growing concerns that bullying and violence come along with the tradition. Reporter Jason Strother has more from Seoul.
Video

Video Comanche People Maintain Pride in Their Heritage

The Comanche (Indian nation) once were called the “Lords of the Plains,” with an empire that included half the land area of current day Texas, large parts of Oklahoma, New Mexico, Kansas and Colorado.The fierceness and battle prowess of these warriors on horseback delayed the settlement of most of West Texas for four decades. VOA’s Greg Flakus reports from Lawton, Oklahoma, that while their warrior days are over, the 15,000 members of the Comanche Nation remain a proud people.
Video

Video Turkey Campus Attacks Raise Islamic Radicalization Fears

Concerns are growing in Turkey of Islamic radicalization at some universities, after clashes between supporters of the jihadist group Islamic State (IS) or ISIS, and those opposed to the extremists. Pro-jihadist literature is on sale openly on the streets of Istanbul. Critics accuse the government of turning a blind eye to radicalism at home, while Kurds accuse the president of supporting IS - a charge strongly denied. Henry Ridgwell reports from London.
Video

Video Syrian Defector Leaks Shocking Photos of Torture Victims

Shocking photographs purporting to show Syrian torture victims are on display at the U.S. Holocaust Memorial Museum in Washington. The museum says the graphic images are among thousands of photographs recently smuggled out of Syria by a military policeman-turned-defector. As VOA reporter Julie Taboh reports, the museum says the photos provide further evidence of atrocities committed by the government of Syrian President Bashar al-Assad against its own people.
Video

Video Drought-Stricken California Considers Upgrading Water System

A three-year drought in California is causing a water shortage that is being felt on farms and cities throughout the state. As VOA's Mike O’Sullivan reports, water experts, consumers and farmers say California needs to make changes to cope with an uncertain future.
Video

Video TechShop Puts High-tech Dreams Within Reach

Square, a business app and card reader, makes it possible to do credit card transactions through cell phones. But what made Square possible? VOA’s Adrianna Zhang and Enming Liu have the answer.
Video

Video Church for Atheists Goes Global

Atheists, by definition, do not believe in God. So they should have no need of a church. But two years ago, a pair of British stand-up comedians decided to create one. Sanderson Jones and Pippa Evans told the BBC they envisioned “something like church but without God". Their “Sunday Assembly” movement has grown from a single congregation in London to dozens of churches around the world. Reporter Mike Osborne visited with the members of a Sunday Assembly that now meets regularly in Nashville.
Video

Video Robot Locates Unexploded Underwater Mines

Many educators believe that hands-on experience is the best way to learn. Proving that the method works is a project developed by a group of students at the Stevens Institute of Technology, in Hoboken, New Jersey. They rose up to a challenge posted by the U.S. Department of Defense and successfully designed and built an underwater robot for locating submerged unexploded ordnance. VOA’s George Putic reports.
Video

Video Liberia's JFK Hospital Reopens After Temporary Ebola Exposure

JFK Hospital is Liberia’s largest and one of its oldest medical facilities. The hospital had to close temporarily following the deaths of two leading doctors from Ebola. It is now getting back on its feet, with the maternity ward being the first section to reopen. Benno Muchler has more for VOA News from Monrovia.
Video

Video Hong Kong Protests Expose Generation Gap

Most of the tens of thousands of protesters in Hong Kong are students seeking democracy. Idealistic youths say while the older generation worries about the present, they are fighting for the territory's future. VOA's Daniel Schearf reports from Hong Kong.
Video

Video Liberians Living in US Struggle From Afar as Ebola Ravages Homeland

More than 8,000 Liberians live in New York City, more than in any other city outside of Liberia itself. As VOA’s Bernard Shusman reports, with the Ebola virus ravaging their homeland, there is no peace of mind for these New Yorkers.
Video

Video Kurds See War-Ravaged Kobani As Political, Emotional Heartland

Intense fighting is continuing between Islamic State militants -- also known as ISIS or ISIL -- and Kurdish forces around the Syrian town of Kobani, on the Turkish border. The U.S. said it carried out at least nine airstrikes against Islamic State positions Friday. Meanwhile the U.N. has warned that hundreds of civilians would be massacred if the town falls to the militants. Henry Ridgwell looks at the strategic significance of the city.

All About America

AppleAndroid