Earths 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. Todays 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 Earths 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. Ravelos 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 cant 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 cant 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 Earths 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 didnt respond very strongly to small perturbations, because there werent 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."
Ravelos 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, firstname.lastname@example.org, 703/292-8580
Tim Stephens | NSF
NASA examines newly formed Tropical Depression 3W in 3-D
26.04.2017 | NASA/Goddard Space Flight Center
Early organic carbon got deep burial in mantle
25.04.2017 | Rice University
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
26.04.2017 | Materials Sciences
26.04.2017 | Agricultural and Forestry Science
26.04.2017 | Physics and Astronomy