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 Research icebreaker Polarstern begins the Antarctic season
09.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

nachricht Far fewer lakes below the East Antarctic Ice Sheet than previously believed
08.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A Chip with Blood Vessels

Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.

Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...

Im Focus: A Leap Into Quantum Technology

Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.

In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...

Im Focus: Research icebreaker Polarstern begins the Antarctic season

What does it look like below the ice shelf of the calved massive iceberg A68?

On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.

Im Focus: Penn engineers develop ultrathin, ultralight 'nanocardboard'

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure

Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...

Im Focus: Coping with errors in the quantum age

Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly

The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

“3rd Conference on Laser Polishing – LaP 2018” Attracts International Experts and Users

09.11.2018 | Event News

On the brain’s ability to find the right direction

06.11.2018 | Event News

European Space Talks: Weltraumschrott – eine Gefahr für die Gesellschaft?

23.10.2018 | Event News

 
Latest News

The dawn of a new era for genebanks - molecular characterisation of an entire genebank collection

13.11.2018 | Life Sciences

Fish recognize their prey by electric colors

13.11.2018 | Life Sciences

Ultrasound Connects

13.11.2018 | Awards Funding

VideoLinks
Science & Research
Overview of more VideoLinks >>>