"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
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 reports about: > Ancient Global Cooling > Arctic Ocean > Climate change > Gates Foundation > Geoscience > cooling trend > global cooling > greenhouse gas > lake sediments > long-term cooling trend > long-term global cooling trend > sea surface temperature > temperature change > temperature fluctuation > water molecule
GPM sees deadly tornadic storms moving through US Southeast
01.12.2016 | NASA/Goddard Space Flight Center
Cyclic change within magma reservoirs significantly affects the explosivity of volcanic eruptions
30.11.2016 | Johannes Gutenberg-Universität Mainz
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy