Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Leading climate scientists reaffirm view that late 20th Century warming was unusual

08.07.2003


Warming resulted in part fromfrom human activity



A group of leading climate scientists has reaffirmed the "robust consensus view" emerging from the peer reviewed literature that the warmth experienced on at least a hemispheric scale in the late 20th century was an anomaly in the previous millennium and that human activity likely played an important role in causing it. In so doing, they refuted recent claims that the warmth of recent decades was not unprecedented in the context of the past thousand years.

Writing in the 8 July issue of the American Geophysical Union publication Eos, Michael Mann of the University of Virginia and 12 colleagues in the United States and United Kingdom endorse the position on climate change and greenhouse gases taken by AGU in 1998. Specifically, they say that "there is a compelling basis for concern over future climate changes, including increases in global-mean surface temperatures, due to increased concentrations of greenhouse gases, primarily from fossil-fuel burning."


The Eos article is a response to two recent and nearly identical papers by Drs. Willie Soon and Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics, published in Climate Research and Energy & Environment (the latter paper with additional co-authors). These authors challenge the generally accepted view that natural factors cannot fully explain recent warming and must have been supplemented by significant human activity, and their papers have received attention in the media and in the U.S. Senate. Requests from reporters to top scientists in the field, seeking comment on the Soon and Baliunas position, lead to memoranda that were later expanded into the current Eos article, which was itself peer reviewed.

Paleoclimatologists (scientists who study ancient climates) generally rely on instrumental data for the past 150 years and "proxy" indicators, such as tree rings, ice cores, corals, and lake sediments to reconstruct the climate of earlier times. Most of the available data pertain to the northern hemisphere and show, according to the authors, that the warmth of the northern hemisphere over the past few decades is likely unprecedented in the last 1,000 years and quite possibly in the preceding 1,000 years as well.

Climate model simulations cannot explain the anomalous late 20th century warmth without taking into account the contributions of human activities, the authors say. They make three major points regarding Soon and Baliunas’s recent assertions challenging these findings.

First, in using proxy records to draw inferences about past climate, it is essential to assess their actual sensitivity to temperature variability. In particular, the authors say, Soon and Baliunas misuse proxy data reflective of changes in moisture or drought, rather than temperature, in their analysis.

Second, it is essential to distinguish between regional temperature anomalies and hemispheric mean temperature, which must represent an average of estimates over a sufficiently large number of distinct regions. For example, Mann and his co- authors say, the concepts of a "Little Ice Age" and "Medieval Warm Period" arose from the Eurocentric origins of historic climatology. The specific periods of coldness and warmth differed from region to region and as compared with data for the northern hemisphere as a whole.

Third, according to Mann and his colleagues, it is essential to define carefully the modern base period with which past climate is to be compared and to identify and quantify uncertainties. For example, they say, the most recent report of the Intergovernmental Panel on Climate Change (IPCC) carefully compares data for recent decades with reconstructions of past temperatures, taking into account the uncertainties in those reconstructions. IPCC concluded that late 20th century warmth in the northern hemisphere likely exceeded that of any time in the past millennium. The method used by Soon and Baliunas, they say, considers mean conditions for the entire 20th century as the base period and determines past temperatures from proxy evidence not capable of resolving trends on a decadal basis. It is therefore, they say, of limited value in determining whether recent warming in anomalous in a long term and large scale context.

The Eos article started as a memorandum that Michael Oppenheimer and Mann drafted to help inform colleagues who were being contacted by members of the media regarding the Soon and Baliunas papers and wanted an opinion from climate scientists and paleoclimatologists who were directly familiar with the underlying issues.

Mann and Oppenheimer learned that a number of other colleagues, including Tom Wigley of the University Corporation for Atmospheric Research (UCAR) in Boulder, Colorado; Philip Jones of the University of East Anglia’s Climatic Research Unit in Norwich, United Kingdom; and Raymond Bradley of the University of Massachusetts in Amherst were receiving similar media requests for their opinions on the matter. Their original memorandum evolved into a more general position paper jointly authored by a larger group of leading scientists in the field.

Mann says he sees the resulting Eos article as representing an even broader consensus of the viewpoint of the mainstream climate research community on the question of late 20th century warming and its causes. The goal of the authors, he says, is to reaffirm support for the AGU position statement on climate change and greenhouse gases and clarify what is currently known from the paleoclimate record of the past one-to-two thousand years and, in particular, what the bearing of this evidence is on the issue of the detection of human influence on recent climate change.

Harvey Leifert | AGU
Further information:
http://www.agu.org/

More articles from Earth Sciences:

nachricht NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center

nachricht Steep rise of the Bernese Alps
24.03.2017 | Universität Bern

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>