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
Greenland ice flow likely to speed up: New data assert glaciers move over sediment, which gets more slippery as it gets wetter
17.08.2017 | Swansea University
Climate change: In their old age, trees still accumulate large quantities of carbon
17.08.2017 | Universität Hamburg
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences