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

24.04.2013
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 pwest@nsf.gov
Program Contacts
Paul E. Filmer, NSF (703) 292-8551 pfilmer@nsf.gov
Neil R. Swanberg, NSF (703) 292-8029 nswanber@nsf.gov
Principal Investigators
Darrell S. Kaufman, Northern Arizona University (928) 523-7192 Darrell.Kaufman@nau.edu

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:
http://www.nsf.gov
http://www.nsf.gov/news/news_summ.jsp?cntn_id=127658&org=NSF&from=news

More articles from Earth Sciences:

nachricht Modeling magma to find copper
13.01.2017 | Université de Genève

nachricht What makes erionite carcinogenic?
13.01.2017 | Friedrich-Schiller-Universität Jena

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

Im Focus: Bacterial Pac Man molecule snaps at sugar

Many pathogens use certain sugar compounds from their host to help conceal themselves against the immune system. Scientists at the University of Bonn have now, in cooperation with researchers at the University of York in the United Kingdom, analyzed the dynamics of a bacterial molecule that is involved in this process. They demonstrate that the protein grabs onto the sugar molecule with a Pac Man-like chewing motion and holds it until it can be used. Their results could help design therapeutics that could make the protein poorer at grabbing and holding and hence compromise the pathogen in the host. The study has now been published in “Biophysical Journal”.

The cells of the mouth, nose and intestinal mucosa produce large quantities of a chemical called sialic acid. Many bacteria possess a special transport system...

Im Focus: Newly proposed reference datasets improve weather satellite data quality

UMD, NOAA collaboration demonstrates suitability of in-orbit datasets for weather satellite calibration

"Traffic and weather, together on the hour!" blasts your local radio station, while your smartphone knows the weather halfway across the world. A network of...

Im Focus: Repairing defects in fiber-reinforced plastics more efficiently

Fiber-reinforced plastics (FRP) are frequently used in the aeronautic and automobile industry. However, the repair of workpieces made of these composite materials is often less profitable than exchanging the part. In order to increase the lifetime of FRP parts and to make them more eco-efficient, the Laser Zentrum Hannover e.V. (LZH) and the Apodius GmbH want to combine a new measuring device for fiber layer orientation with an innovative laser-based repair process.

Defects in FRP pieces may be production or operation-related. Whether or not repair is cost-effective depends on the geometry of the defective area, the tools...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

Multiregional brain on a chip

16.01.2017 | Power and Electrical Engineering

New technology enables 5-D imaging in live animals, humans

16.01.2017 | Information Technology

Researchers develop environmentally friendly soy air filter

16.01.2017 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>