UCSB Geologist Discovers Pattern in Earth's Long-Term Climate Record

UCSB Geologist Discovers Pattern in Earth's Long-Term Climate Record

April 6, 2010

(Santa Barbara, Calif.) –– In an analysis of the past 1.2 million years, UC Santa Barbara geologist Lorraine Lisiecki discovered a pattern that connects the regular changes of the Earth's orbital cycle to changes in the Earth's climate. The finding is reported in this week's issue of the scientific journal Nature Geoscience.

Lisiecki performed her analysis of climate by examining ocean sediment cores. These cores come from 57 locations around the world. By analyzing sediments, scientists are able to chart the Earth's climate for millions of years in the past. Lisiecki's contribution is the linking of the climate record to the history of the Earth's orbit.

It is known that the Earth's orbit around the sun changes shape every 100,000 years. The orbit becomes either more round or more elliptical at these intervals. The shape of the orbit is known as its "eccentricity." A related aspect is the 41,000-year cycle in the tilt of the Earth's axis.

Glaciation of the Earth also occurs every 100,000 years. Lisiecki found that the timing of changes in climate and eccentricity coincided. "The clear correlation between the timing of the change in orbit and the change in the Earth's climate is strong evidence of a link between the two," said Lisiecki. "It is unlikely that these events would not be related to one another."

Besides finding a link between change in the shape of the orbit and the onset of glaciation, Lisiecki found a surprising correlation. She discovered that the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth's orbit –– and vice versa. She found that the stronger changes in the Earth's orbit correlated to weaker changes in climate. "This may mean that the Earth's climate has internal instability in addition to sensitivity to changes in the orbit," said Lisiecki.

She concludes that the pattern of climate change over the past million years likely involves complicated interactions between different parts of the climate system, as well as three different orbital systems. The first two orbital systems are the orbit's eccentricity, and tilt. The third is "precession," or a change in the orientation of the rotation axis.

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Research Interests

My research focuses on computational approaches to the interpretation of paleoclimate records. I believe that the integrated analysis of widely distributed paleoclimate records will yield important information about the climate system that cannot be obtained by studying these records individually. I am particularly interested in the evolution of Plio-Pleistocene climate as it relates to Milankovitch forcing, 100-kyr glacial cycles, and deep-ocean circulation. I also develop and distribute software related to age model development and stratigraphy. The analytical techniques I use most frequently are stratigraphic correlation, simple physical models, dynamic programming, and mathematical tools such as time series analysis, principal component analysis, and computational probability and statistics.

http://www.lorraine-lisiecki.com/simple.html">What does this mean? Simple, non-technical explanations of what I study and why. Also, PowerPoint slides for teachers.

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What causes glacial cycles?

Glaciers and ice sheets form when winter snow does not completely melt away each summer. Then the next winter's snow falls on top of this old snow, and even more snow is left behind after the next summer. After many years, this small imbalance in snowfall versus melting can create huge ice sheets. Whether or not snow melts completely away each year is primarily controlled by the amount of summer sunlight. This is known as Milankovitch theory.

The amount of sunlight received at a certain location varies with time due to cyclic changes in the Earth's orbit and tilt. These change with time due to the gravitational forces of the moon and the other planets. The three three types of change are tilt (obliquity), precession, and eccentricity. They vary in cycles of 19,000 to 400,000 years. The strongest cycle in summer sunlight in ice-sheet forming regions is 23,000 years caused by precession, but glacial cycles over the last million years are all about 100,000 years long, which is the length of one eccentricity cycle. Before that time, glacial cycles were 41,000 years long, corresponding to the length of the cycle in Earth's tilt. Why the ice sheets respond most strongly to the 41,000 and 100,000 year cycles is one of the biggest mysteries in our field. Read more about http://www.lorraine-lisiecki.com/thesis_appendix.html#1-1-Milankovitch-Theory">Milankovitch theory and http://www.lorraine-lisiecki.com/thesis_appendix.html#1-2-Orbital-Cycles">orbital cycles.

http://www.lorraine-lisiecki.com/orbital_cycles.ppt">Download Power Point slides illustrating the different orbital cycles.

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The main argument in favor of Milankovitch theory is the dominance of precession, obliquity, and eccentricity frequencies in both insolation changes and the climate record. |For opposing viewpoints, see Winograd et al., 1992; Muller and MacDonald, 1997; Wunsch, 2004|. The main challenge is that high-latitude summer insolation is dominated by 19- and 23-kyr precession cycles, but late Pleistocene glacial cycles are 100 kyr and early Pleistocene glacial cycles are 41 kyr. The many variations of Milankovitch theory created to account for this discrepancy are collectively known as theories of orbital forcing, due to their emphasis on the role that Earth's orbital configuration plays in controlling insolation. However, the specific mechanisms by which insolation changes produce observed climate responses are still poorly understood; some recent theories are presented in Section 1.3.

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Abstract

A number of records commonly described as showing control of climate change by Milankovitch insolation forcing are re-examined. The fraction of the record variance attributable to orbital changes never exceeds 20%. In no case, including a tuned core, do these forcing bands explain the overall behavior of the records. At zero order, all records are consistent with stochastic models of varying complexity with a small superimposed Milankovitch response, mainly in the obliquity band. Evidence cited to support the hypothesis that the 100 Ka glacial/interglacial cycles are controlled by the quasi-periodic insolation forcing is likely indistinguishable from chance, given the small sample size and near-integer ratios of 100 Ka to the precessional periods. At the least, the stochastic background ‘‘noise’’ is likely to be of importance.

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6. Summary

The main issue is the small sample size: seven Pleistocene ice ages with six intervals. The resulting record of myriadic climate variability in deep-sea and ice cores is dominated by processes indistinguishable from stochastic, apart from a very small amount (less than 20% and sometimes less than 1%) of the variance attributable to insolation forcing. Climate variability in this range of periods is difficult to distinguish from a form of random walk with small superimposed deterministic elements. Evidence that Milankovitch forcing ‘‘controls’’ the records, in particular the 100 ka glacial/interglacial, is very thin and somewhat implausible, given that most of the high frequency variability lies elsewhere. These results are not a proof of stochastic control of the Pleistocene glaciations, nor that deterministic elements are not in part a factor. But the stochastic behavior hypothesis should not be set aside arbitrarily—as it has at least as strong a foundation as does that of orbital control.

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Black Carbon a Significant Factor in Melting of Himalayan Glaciers

February 03, 2010
Julie Chao 510-486-6491 JHChao@lbl.gov
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The fact that glaciers in the Himalayan mountains are thinning is not disputed. However, few researchers have attempted to rigorously examine and quantify the causes. Lawrence Berkeley National Laboratory scientist Surabi Menon set out to isolate the impacts of the most commonly blamed culprit—greenhouse gases, such as carbon dioxide—from other particles in the air that may be causing the melting. Menon and her collaborators found that airborne black carbon aerosols, or soot, from India is a major contributor to the decline in snow and ice cover on the glaciers.

“Our simulations showed greenhouse gases alone are not nearly enough to be responsible for the snow melt,” says Menon, a physicist and staff scientist in Berkeley Lab’s Environmental Energy Technologies Division. “Most of the change in snow and ice cover—about 90 percent—is from aerosols. Black carbon alone contributes at least 30 percent of this sum.”

Menon and her collaborators used two sets of aerosol inventories by Indian researchers to run their simulations; their results were published online in the journal Atmospheric Chemistry and Physics.

The actual contribution of black carbon, emitted largely as a result of burning fossil fuels and biomass, may be even higher than 30 percent because the inventories report less black carbon than what has been measured by observations at several stations in India. (However, these observations are too incomplete to be used in climate models.) “We may be underestimating the amount of black carbon by as much as a factor of four,” she says.

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