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taken from sources such as tree rings, pollen, corals, lake and marine sediments, ice cores, stalagmites and assorted historical documents taken from 511 locations throughout Earth’s seven continents.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

WHO: Anti-Ebola Efforts Should Focus on West Africa

Official says WHO is 'reasonably confident' countries bordering those hardest hit by the Ebola outbreak are not seeing the virus crossing their borders More

South Sudan Crisis Threatens Development

Economic costs and lost development opportunities in South Sudan have erased what little progress the country has made since independence in 2011 More

Ukraine PM Warns Russia May Try to Disrupt Sunday Poll

Arseniy Yatsenyuk orders full security mobilization for parliamentary election to prevent ‘terrorist acts’ from being carried out More

Featured Videos

Your JavaScript is turned off or you have an old version of Adobe's Flash Player. Get the latest Flash player.
After Decades of Pressure, Luxembourg Drops Bank Secrecy Rulesi
X
October 21, 2014 12:20 AM
European Union finance ministers have reached a breakthrough agreement that will make it more difficult for tax cheats to hide their money. The new legislation, which had been blocked for years by countries with a reputation as tax havens, was approved last week after Luxembourg and Austria agreed to lift their vetoes. But as Mil Arcega reports, it doesn’t mean tax cheats have run out of places to keep their money hidden.
Video

Video After Decades of Pressure, Luxembourg Drops Bank Secrecy Rules

European Union finance ministers have reached a breakthrough agreement that will make it more difficult for tax cheats to hide their money. The new legislation, which had been blocked for years by countries with a reputation as tax havens, was approved last week after Luxembourg and Austria agreed to lift their vetoes. But as Mil Arcega reports, it doesn’t mean tax cheats have run out of places to keep their money hidden.
Video

Video Kobani Refugees Welcome, Turkey Criticizes, US Airdrop

Residents of Kobani in northern Syria have welcomed the airdrop of weapons, ammunition and medicine to Kurdish militia who are resisting the seizure of their city by Islamic State militants. The Turkish government, however, has criticized the operation. VOA’s Scott Bobb reports from southeastern Turkey, across the border from Kobani.
Video

Video China Political Meeting Seeks to Improve Rule of Law

China’s communist leaders will host a top level political meeting this week, called the Fourth Plenum, and for the first time in the party’s history, rule of law will be a key item on the agenda. Analysts and Chinese media reports say the meetings could see the approval of long-awaited measures aimed at giving courts more independence and include steps to enhance an already aggressive and high-reaching anti-corruption drive. VOA’s Bill Ide has more from Beijing.
Video

Video US ‘Death Cafes’ Put Focus on the Finale

In contemporary America, death usually is a topic to be avoided. But the growing “death café” movement encourages people to discuss their fears and desires about their final moments. VOA’s Jerome Socolovsky reports.
Video

Video Ebola Orphanage Opens in Sierra Leone

Sierra Leone's first Ebola orphanage has opened in the Kailahun district. Hundreds of children orphaned since the beginning of the Ebola outbreak face stigma and rejection with nobody to care for them. Adam Bailes reports for VOA about a new interim care center that's aimed at helping the growing number of children affected by Ebola.
Video

Video Young Nairobi Tech Innovator on 'Track' in Security Business

A 24-year-old technology innovator in Nairobi has invented a tracking device that monitors and secures cars. He has also come up with what he claims is the most robust audio-visual surveillance system yet. As Lenny Ruvaga reports from the Kenyan capital, his innovations are offering alternative security solutions.
Video

Video Latinas Converting to Islam for Identity, Structure

Latinos are one of the fastest growing groups in the Muslim religion. According to the Pew Research Center, about 6 percent of American Muslims are Latino. And a little more than half of new converts are female. VOA’s Carolyn Presutti travelled to Miami, Florida -- where two out of every three residents is Hispanic -- to learn more.
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 North Carolina Emerges as Key Election Battleground

U.S. congressional midterm elections will be held on November 4th and most political analysts give Republicans an excellent chance to win a majority in the U.S. Senate, which Democrats now control. So what are the issues driving voters in this congressional election year? VOA National Correspondent Jim Malone traveled to North Carolina, one of the most politically competitive states in the country, to find out.
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.

All About America

AppleAndroid