Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New Findings On Climate Show Gradual Shift To Modern But Increased Sensitivity To Perturbations

21.05.2004

Earth’s climate system is more sensitive to perturbations now than it was in the distant past, according to a study published this week in the journal Nature. The findings suggest a previously unrecognized role for tropical and subtropical regions in controlling the sensitivity of the climate to change.

Christina Ravelo, an ocean scientist at the University of California, Santa Cruz (UCSC) , and her coauthors at UCSC and Boise State University, Idaho, focused on the Pliocene epoch, from about 5 million to 1.8 million years ago, when the climate was significantly warmer, sea levels were higher, and polar ice sheets were smaller than they are today. During the late Pliocene, the climate shifted to the much cooler regime of the Pleistocene, characterized by episodes of extensive glaciation in the Northern Hemisphere. Today’s climate is a relatively warm period within this generally cool climate regime.

The findings have implications for understanding modern climate change. The Pliocene is the most recent period in Earth’s history with warmer temperatures than today and comparable concentrations of greenhouse gases, so it offers a tempting analogy for future climate change. But the Pliocene was a very different time in terms of circulation patterns and sensitivity to climate change, Ravelo said.

Traditional explanations for the transition from the warm Pliocene to the cool Pleistocene have focused on single events- such as the uplifting of mountain ranges or separation of ocean basins--that may have altered global circulation patterns and tipped the climate system beyond some threshold, resulting in a new climate regime. Ravelo’s findings, however, point toward a gradual process in which shifts in major components of the climate system occurred at different times in different regions.

"We found evidence of regional responses that can’t be explained by a domino effect. The transition took about 2 million years, and there is no way one event could have led to that," Ravelo said.

Added Amos Winter, program director in the National Science Foundation (NSF)’s marine geology and geophysics program, which funded the research, "There is a big debate regarding the mechanisms and rates of climate change from the warm Pliocene to the cool Pleistocene. Using deep-sea sediment cores to reconstruct climate over the last 5 million years, Ravelo and colleagues demonstrate that the transition can’t be explained by a single event, as previously had been thought."

The researchers analyzed sediment cores from the ocean floor for evidence of climate conditions during the Pliocene. Fossils of microscopic plankton preserved in the sediments hold records of ocean temperatures and seasonal variability. Even the extent of glaciation on land can be determined from oxygen isotope ratios in the calcite shells of marine plankton.

When they compared climate trends at different latitudes, the researchers found that tropical conditions remained stable while a major shift took place at higher latitudes. The onset of significant glaciation in the Northern Hemisphere took place about 2.75 million years ago, accompanied by cooling in subtropical regions. Significant changes in the tropics were not seen until a million years later, when conditions in the tropics and subtropics switched to the patterns of ocean temperatures and atmospheric circulation that persist today.

With this transition to the modern mode of circulation in the tropics and subtropics, the global climate system seems to have become much more sensitive to small perturbations. On short timescales, for example, dramatic swings in climate known as El Niño and La Niña are triggered by periodic changes in the equatorial waters of the Pacific.

On longer timescales, the comings and goings of the glacial ice sheets over hundreds of thousands of years during the Pleistocene correlate with cyclical changes in solar heating of the planet related to cycles in Earth’s orbit around the Sun. Climatologists refer to such effects as "solar forcing." But during the Pliocene, the same cyclic changes in solar heating took place without corresponding swings in the global climate.

"Small changes in the solar budget gave large climate responses during the Pleistocene, which we now think is related to conditions in tropical regions that create strong feedbacks between the ocean and the atmosphere," Ravelo said. "During the Pliocene, the system didn’t respond very strongly to small perturbations, because there weren’t these feedback mechanisms embedded in the atmospheric and oceanic circulation patterns."

The ultimate cause of the transition from Pliocene to Pleistocene climate regimes is still unknown. A likely candidate, however, is a gradual decline in the concentration of greenhouse gases in the atmosphere, Ravelo said.

"The forcing must have been gradual, and different places went through this major transition in the climate at different times because of distinct regional responses to the global forcing.

"If we use that time period as an analogy for the future, we need to understand that we are looking at a climate system that is really quite different than today," she said. "And whatever happens in the future, if there are significant changes in the lower latitudes, that could have major effects on the global climate system."

Ravelo’s coauthors include Dyke Andreason, formerly a graduate student at UCSC and now at Rutgers University; Mitchell Lyle and Annette Olivarez Lyle of Boise State University; and UCSC graduate student Michael Wara.

NSF Program Contact: Amos Winter, awinter@nsf.gov, 703/292-8580

Tim Stephens | NSF
Further information:
http://www.nsf.gov

More articles from Earth Sciences:

nachricht Tracking down climate change with radar eyes
17.07.2019 | Technical University of Munich (TUM)

nachricht New sensor could shake up earthquake response efforts
11.07.2019 | DOE/Lawrence Berkeley National Laboratory

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Megakaryocytes act as „bouncers“ restraining cell migration in the bone marrow

Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.

Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...

Im Focus: Artificial neural network resolves puzzles from condensed matter physics: Which is the perfect quantum theory?

For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.

Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...

Im Focus: Extremely hard yet metallically conductive: Bayreuth researchers develop novel material with high-tech prospects

An international research group led by scientists from the University of Bayreuth has produced a previously unknown material: Rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications. Indeed, it is a super-hard metallic conductor that can withstand extremely high pressures like a diamond. A process now developed in Bayreuth opens up the possibility of producing rhenium nitride pernitride and other technologically interesting materials in sufficiently large quantity for their properties characterisation. The new findings are presented in "Nature Communications".

The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was...

Im Focus: Modelling leads to the optimum size for platinum fuel cell catalysts: Activity of fuel cell catalysts doubled

An interdisciplinary research team at the Technical University of Munich (TUM) has built platinum nanoparticles for catalysis in fuel cells: The new size-optimized catalysts are twice as good as the best process commercially available today.

Fuel cells may well replace batteries as the power source for electric cars. They consume hydrogen, a gas which could be produced for example using surplus...

Im Focus: The secret of mushroom colors

Mushrooms: Darker fruiting bodies in cold climates

The fly agaric with its red hat is perhaps the most evocative of the diverse and variously colored mushroom species. Hitherto, the purpose of these colors was...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Tracking down climate change with radar eyes

17.07.2019 | Earth Sciences

Researchers build transistor-like gate for quantum information processing -- with qudits

17.07.2019 | Information Technology

A new material for the battery of the future, made in UCLouvain

17.07.2019 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>