Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Slowdown of global warming fleeting


The recent slowdown in the warming rate of the Northern Hemisphere may be a result of internal variability of the Atlantic Multidecadal Oscillation -- a natural phenomenon related to sea surface temperatures, according to Penn State researchers.

"Some researchers have in the past attributed a portion of Northern Hemispheric warming to a warm phase of the AMO," said Michael E. Mann, Distinguished Professor of Meteorology. "The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming temporarily."

According to Mann, the problem with the earlier estimates stems from having defined the AMO as the low frequency component that is left after statistically accounting for the long-term temperature trends, referred to as detrending.

"Initial investigations into the multidecadal climate oscillation in the North Atlantic were hampered by the short length of the instrumental climate record which was only about a century long," said Mann. "And some of the calculations were contaminated by long-term climate trends driven or forced by human factors such as greenhouse gases as well as pollutants known as sulfate aerosols. These trends masqueraded as an apparent oscillation."

Mann and his colleagues took a different approach in defining the AMO, which they report online in a special "Frontier" paper in Geophysical Research Letters. They compared observed temperature variation with a variety of historic model simulations to create a model for internal variability of the AMO that minimizes the influence of external forcing -- including greenhouse gases and aerosols. They call this the differenced-AMO because the internal variability comes from the difference between observations and the models' estimates of the forced component of North Atlantic temperature change. They found that their results for the most recent decade fall within expected multidecadal variability.

They also constructed plausible synthetic Northern Hemispheric mean temperature histories against which to test the differenced-AMO approaches. Because the researchers know the true AMO signal for their synthetic data from the beginning, they could demonstrate that the differenced-AMO approach yielded the correct signal. They also tested the detrended-AMO approach and found that it did not come up with the known internal variability.

The detrended approach produced an AMO signal with increased amplitude -- both high and low peaks were larger than in the differenced-AMO signal and in the synthetic data. They also found that the peaks and troughs of the oscillation were skewed using the detrending approach, causing the maximums and minimums to occur at different times than in the differenced-AMO results. While the detrended-AMO approach produces a spurious temperature increase in recent decades, the differenced approach instead shows a warm peak in the 1990s and a steady cooling since.

Past researchers have consequently attributed too much of the recent North Atlantic warming to the AMO and too little to the forced hemispheric warming, according to the researchers.

Mann and his team also looked at supposed "stadium waves" suggested by some researchers to explain recent climate trends. The putative climate stadium wave is likened to the waves that go through a sports stadium with whole sections of fans rising and sitting together, propagating a wave around the oval. Random motion of individuals suddenly becomes unified action.

The climate stadium wave supposedly occurs when the AMO and other related climate indicators synchronize, peaking and waning together. Mann and his team show that this apparent synchronicity is likely a statistical artifact of using the problematic detrended-AMO approach.

"We conclude that the AMO played at least a modest role in the apparent slowing of warming during the past decade," said Mann. "As the AMO is an oscillation, this cooling effect is likely fleeting, and when it reverses, the rate of warming increases." Others working on this project were Byron A. Steinman, postdoctoral fellow in meteorology, and Sonya K. Miller, programmer/analyst, meteorology, Penn State.

The National Science Foundation supported this work.

A'ndrea Elyse Messer | EurekAlert!
Further information:

Further reports about: Atlantic Hemispheric estimates gases greenhouse individuals oscillation synthetic temperature waves

More articles from Earth Sciences:

nachricht Rapid plankton growth in ocean seen as sign of carbon dioxide loading
27.11.2015 | Johns Hopkins University

nachricht Revealing glacier flow with animated satellite images
26.11.2015 | European Geosciences Union

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Climate study finds evidence of global shift in the 1980s

Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.

Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...

Im Focus: Innovative Photovoltaics – from the Lab to the Façade

Fraunhofer ISE Demonstrates New Cell and Module Technologies on its Outer Building Façade

The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...

Im Focus: Lactate for Brain Energy

Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.

In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...

Im Focus: Laser process simulation available as app for first time

In laser material processing, the simulation of processes has made great strides over the past few years. Today, the software can predict relatively well what will happen on the workpiece. Unfortunately, it is also highly complex and requires a lot of computing time. Thanks to clever simplification, experts from Fraunhofer ILT are now able to offer the first-ever simulation software that calculates processes in real time and also runs on tablet computers and smartphones. The fast software enables users to do without expensive experiments and to find optimum process parameters even more effectively.

Before now, the reliable simulation of laser processes was a job for experts. Armed with sophisticated software packages and after many hours on computer...

Im Focus: Quantum Simulation: A Better Understanding of Magnetism

Heidelberg physicists use ultracold atoms to imitate the behaviour of electrons in a solid

Researchers at Heidelberg University have devised a new way to study the phenomenon of magnetism. Using ultracold atoms at near absolute zero, they prepared a...

All Focus news of the innovation-report >>>



Event News

Fraunhofer’s Urban Futures Conference: 2 days in the city of the future

25.11.2015 | Event News

Gluten oder nicht Gluten? Überempfindlichkeit auf Weizen kann unterschiedliche Ursachen haben

17.11.2015 | Event News

Art Collection Deutsche Börse zeigt Ausstellung „Traces of Disorder“

21.10.2015 | Event News

Latest News

Siemens to supply 126 megawatts to onshore wind power plants in Scotland

27.11.2015 | Press release

Two decades of training students and experts in tracking infectious disease

27.11.2015 | Life Sciences

Coming to a monitor near you: A defect-free, molecule-thick film

27.11.2015 | Materials Sciences

More VideoLinks >>>