Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Analysis of 2,000 Years of Climate Records Finds Global Cooling Trend Ended in the 19th Century

20th-century warming, researchers say, "reversed" the trend
The most comprehensive evaluation of temperature change on Earth’s continents over the past 1,000 to 2,000 years indicates that a long-term cooling trend--caused by factors including fluctuations in the amount and distribution of heat from the sun, and increases in volcanic activity--ended late in the 19th century.

The study also finds that the 20th century ranks as the warmest or nearly the warmest century on all of the continents, except Antarctica. Africa had insufficient data to be included in the analysis.
Global warming that has occurred since the end of the 19th century reversed a persistent long-term global cooling trend, say the researchers.

A consortium of 78 authors from 24 countries, some of them supported by the National Science Foundation (NSF), also note in research published in the May 2013 issue of the journal Nature Geoscience that there were regional differences in temperature evolution.

"This is an example of a large international team effort, collaborating to synthesize new scientific results from a very large, publicly available dataset," said Paul E. Filmer, program director for the Paleoclimate, Sedimentary Geology and Paleobiology and ArcSEES programs in NSF's Geosciences Directorate.

The researchers are members of the "2K Network" of the International Geosphere Biosphere Program (IGBP) Past Global Changes (PAGES) project. The Swiss National Science Foundation and the US NSF jointly support the PAGES International Project Office.

"Global warming that has occurred since the end of the 19th century reversed a persistent long-term global cooling trend," the researchers write in the report.

Because long-range cooling was caused by natural factors that continued to exist in the 20th century, the authors argue, the warming of the 20th century makes it more difficult to discount the effects of the increase of greenhouse gases in the global increase of temperatures measured in recent decades.

However, the researchers note, their study was not specifically designed to assess the extent to which temperature changes can be attributed to various natural and human-caused factors.

"The new results show that climate change is, as usual, more complicated than we expected: long, millennial natural cooling trends were punctuated by warming episodes that turned out to be more local than we thought," Filmer said.

"The natural forces driving the cooling are still present today, but since the nineteenth century an additional, stronger, warming driver has been added: human activity. We cannot match the temperature records since then without factoring in this new driver."

The PAGES 2K study aggregates proxy data, or information from a variety of sources that stand in for actual temperature measurements of past climate.

These primarily include tree-ring analysis, which provides a picture of growth, which in turn is based in part on air temperatures; tree pollen, which registers changes in dominant species; dome corals, which register sea surface temperatures in their annually banded skeletons; the make-up of water molecules contained in ice cores from the Arctic, Antarctic and glaciers in the temperate regions of the globe; and various physical and biological properties of lake sediments.

Darrell S. Kaufman, an NSF-funded researcher at the School of Earth Sciences and Environmental Sustainability at Northern Arizona University and the lead co-author of the PAGES research, focuses on climate signals as recorded in arctic lake sediments.

His NSF-supported grant, Nonlinearities in the Arctic climate system during the Holocene focuses on how climate feedbacks and perturbations result in rapid changes.

"The predominant long-term cooling trend is common in proxy records we study in Alaska and elsewhere in the Arctic. Finding it at lower latitudes and especially in the southern hemisphere was surprising and has important implications for our understanding of the processes that drive climate change."

Coauthor Nicholas McKay, a postdoctoral scholar working with Kaufman at Northern Arizona University, added "my role in the study was to make sure that the patterns we were observing in the data were robust features of the dataset."

Added McKay: "The primary results: The long-term cooling trend, the century-scale differences between regions, and the warmth of the 20th century, are apparent no matter how you look at the data."

The Division of Polar Programs in the Geosciences Directorate supports both Kaufman and McKay.

The PAGES 2K Network analysis focuses on the last 2,000 years because temperatures are well represented in proxy records. Beyond 2,000 years ago, the abundance of information about climate variability decreases and fundamental features of the climatic system diverge from more recent conditions.

While the researchers do not make explicit correlations in their study between the levels of greenhouse gases in the atmosphere during the 20th century and the increased global temperatures, they note that their analysis will serve as a benchmark for future studies.

"Our reconstructions and proxy data compilation," they write, "will be useful in future studies, serving as a benchmark for comparisons with climate-model simulations aimed at understanding the cause of global cooling, and the extent to which externally forced and unforced variability can explain temperature fluctuations at the continental scale."

Additional information about the study is available at the PAGES Website.

Media Contacts
Peter West, NSF (703) 292-7530
Program Contacts
Paul E. Filmer, NSF (703) 292-8551
Neil R. Swanberg, NSF (703) 292-8029
Principal Investigators
Darrell S. Kaufman, Northern Arizona University (928) 523-7192

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2012, its budget was $7.0 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives about 50,000 competitive requests for funding, and makes about 11,500 new funding awards. NSF also awards about $593 million in professional and service contracts yearly.

Peter West | EurekAlert!
Further information:

More articles from Earth Sciences:

nachricht Receding glaciers in Bolivia leave communities at risk
20.10.2016 | European Geosciences Union

nachricht UM researchers study vast carbon residue of ocean life
19.10.2016 | University of Miami Rosenstiel School of Marine & Atmospheric Science

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>