Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
ABSTRACT: Successful prediction of future global climate is critically dependent on understanding its complex history, some of which is displayed in paleoclimate time series extracted from deep-sea sediment and ice cores. These recordings exhibit frequent episodes of abrupt climate change believed to be the result of nonlinear response of the climate system to internal or external forcing, yet, neither the physical mechanisms nor the nature of the nonlinearities involved are well understood. At the orbital (104 –105 years) and millennial scales, abrupt climate change appears as sudden, rapid warming events, each followed by periods of slow cooling. The sequence often forms a distinctive saw-tooth shaped time series, epitomized by the deep-sea records of the last million years and the Dansgaard–Oeschger (D/O) oscillations of the last glacial. Here I introduce a simplified mathematical model consisting of a novel arrangement of coupled nonlinear differential equations that appears to capture some important physics of climate change at Milankovitch and millennial scales, closely reproducing the saw-tooth shape of the deep-sea sediment and ice core time series, the relatively abrupt mid-Pleistocene climate switch, and the intriguing D/O oscillations. Named LODE for its use of the logistic-delayed differential equation, the model combines simplicity in the formulation (two equations, small number of adjustable parameters) and sufficient complexity in the dynamics (infinite-dimensional nonlinear delay differential equation) to accurately simulate details of climate change other simplified models cannot. Close agreement with available data suggests that the D/O oscillations are frequency modulated by the third harmonic of the precession forcing, and by the precession itself, but the entrained response is intermittent, mixed with intervals of noise, which corresponds well with the idea that the climate operates at the edge between chaos and order. LODE also predicts a persistent ~1.5 ky oscillation that results from the frequency modulated regional climate oscillation.
ABSTRACT: Most paleoclimate researchers would probably agree that variations in Earth's axial tilt and precession parameters have influenced past climate change. However, claims of connections between orbital eccentricity and ice age climate are more difficult to demonstrate or accept, especially since the amplitude of the strongest component of eccentricity-induced insolation, the 413-ky signal, is conspicuously small or absent from the power spectra of the last million years of paleoclimate data, and climate models without external forcing can easily reproduce the main ~100-ky cycles of the late Pleistocene and Holocene. Here I show that it is possible to tease out the 413-ky component of eccentricity directly from orbitally untuned deep-sead18 O time series, and that the signal is strong, albeit buried deep in thed18 O time series, concealed by frequency modulation (FM). To extract the 413-ky signal, the data is frequency and phase demodulated numerically, while synthetic surrogate time series with properties believed similar to the actual data are used to test the nature of the modulator and the accuracy of each step in the inversion.
ABSTRACT: The cause of the 100 kyr glacial–interglacial cycles during the past 800 kyr is one of the fundamental puzzles in paleoclimatology. The widely accepted Milankovitch theory, relating earth's climate cycles to variations in insolation caused by periodic changes in orbital parameters, has difficulties to explain the predominant 100 kyr rhythm. Although earth's eccentricity varies with a period of 100 kyr, the resulting change in insolation is too small to produce the corresponding climate cycle by direct forcing (Imbrie et al., Paleoceanography 8 (1993) 699). In order to solve the 100 kyr problem', Muller and MacDonald (Nature 377 (1995) 107; Science 277 (1997a) 215; Proc. Nat. Acad. Sci. USA 94 (1997b) 8329) proposed an alternative orbital but non-Milankovitch mechanism attributing the glacial cycles to regular variations in the accretion of interplanetary dust particles (IDP) caused by 100 kyr cycles in the orbital inclination of the earth. To test this controversial hypothesis, we study the IDP accumulation in deep-sea sediments from a period in the early Pleistocene. We find apparent 41 kyr cycles but no 100 kyr periodicity in the IDP accumulation rate. As there is no known mechanism to produce 41 kyr cycles in IDP supply from space, we conclude that the 41 kyr cycles are caused by the dynamics of sediment accumulation, and that changes in the IDP flux do not drive the Pleistocene glacial cycles.
ABSTRACT: The late Paleocene thermal maximum (LPTM) is associated with a brief, but intense, interval of global warming and a massive perturbation of the global carbon cycle. We have developed a new orbital chronology for Ocean Drilling Program (ODP) Site 690 (Weddell Sea, Southern Ocean) by using spectral analysis of high-resolution geochemical records. The LPTM interval spans 11 precessional cycles yielding a duration of 210 to 220 k.y. Thed13 C anomaly associated with the LPTM has a magnitude of about -2.5‰ to -3‰; we show that about -2‰ of the excursion occurs within two steps that each were less than 1000 yr in duration. The remainder developed through a series of steps over 52 k.y. The timing of these steps is consistent with a series of nearly catastrophic releases of methane from gas hydrates, punctuated by intervals of relative equilibria between hydrate dissociation and carbon burial. Further, we are able to correlate the records between ODP Sites 690 and 1051 (western North Atlantic) on the scale of 21 k.y. cycles, which demonstrates that the details of thed13 C excursion are recognizable between distant sites. Comparison of cycle records at Sites 690 and 1051 suggests that sediment representing the interval 30 k.y. just prior to and at the onset of the LPTM are missing in the latter location. This unconformity probably resulted from slope failure accompanying methane hydrate dissociation within 10 k.y. of the start of the LPTM.
N. G. Pisias, A. C. Mix, L. Heusser (2001). Millennial scale climate variability of the northeast Pacific Ocean and northwest North America based on radiolaria and pollen. Quaternary Science Reviews 20 (14): 1561-1576
ABSTRACT: Radiolaria and pollen abundances in marine sediment cores from the northeast Pacific are used to reconstruct oceanographic and continental climate change during the past glacial cycle (0–150 kyr). These data allow direct comparison of the climate response of continental and oceanic systems. Detailedd18 O and AMS-14 C measurements provide a link into global stratigraphic frameworks. Canonical correlation analysis extracts two modes of variation common to both the Radiolaria and pollen records. The first mode of variation correlates an assemblage of Radiolaria associated with coastal upwelling with increased redwood, western hemlock, and alder pollen. This association is consistent with the modern relationship between coastal upwelling, coastal fog and redwood forests. A second canonical mode relates an oceanic fauna now found in highest abundance in the far North Pacific with reduced pine and western hemlock pollen abundance.
Comparison of these records to an ice cored18 O record suggests that at wavelengths >3000 years, warm events in Greenland are correlated to intervals of increased coastal upwelling off Oregon, decreases in importance of very cold North Pacific fauna (suggesting warming), and increases in pollen associated with wetter coastal environments. Radiolarian based sea-surface temperature estimates suggest that the variability of the northeast Pacific on this time scale is about 2°C. Warming in the coastal regions reflects reduced advection of the California Current, but is moderated by increases in cool coastal upwelling. We infer that the response of the northeast Pacific to millennial scale climate changes is related to changes in atmospheric circulation at mid- to high latitudes.
Preliminary analysis suggests that oceanic variability off Oregon at wavelengths <3000 years is similar to the Dansgaard–Oeschger cycles of the ice cored18 O records. This variability is associated with changes in subtropical faunal elements without similar changes in other faunal elements. This finding suggests that, unlike longer-period millennial scale events, the propagation of the shorter wavelength events to the Northeast Pacific is through subtropical or tropical teleconnections.
Bond, G., W. Showers, M. Chaseby, R. Lotti, P. Almasi, P. deMinocal, P. Priore, H. Cullen, I. Hajdas, G. Bonani (1997). Pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science 278 (5341): 1257-1266
INTRODUCTION: Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what is conventionally thought to have been a relatively stable Holocene climate. During each of these episodes, cool, ice-bearing waters from north of Iceland were advected as far south as the latitude of Britain. At about the same times, the atmospheric circulation above Greenland changed abruptly. Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together, they make up a series of climate shifts with a cyclicity close to 1470 ± 500 years. The Holocene events, therefore, appear to be the most recent manifestation of a pervasive millennial-scale climate cycle operating independently of the glacial-interglacial climate state. Amplification of the cycle during the last glaciation may have been linked to the North Atlantic's thermohaline circulation.
Cortese, G., A. Abelmann, R. Gersonde (2007). The last five glacial-interglacial transitions: A high-resolution 450,000-year record from the subantarctic Atlantic. Paleoceanography 22 (PA4203): doi:10.1029/2007PA001457
ABSTRACT: A submillennial resolution, radiolarian-based record of summer sea surface temperature (SST) documents the last five glacial to interglacial transitions at the subtropical front, southern Atlantic Ocean. Rapid fluctuations occur both during glacial and interglacial intervals, and sudden cooling episodes at glacial terminations are recurrent. Surface hydrography and global ice volume proxies from the same core suggest that summer SST increases prior to terminations lead global ice-volume decreases by 4.7 ± 3.7 ka (in the eccentricity band), 6.9 ± 2.5 ka (obliquity), and 2.7 ± 0.9 ka (precession). A comparison between SST and benthicd13 C suggests a decoupling in the response of northern subantarctic surface, intermediate, and deep water masses to cold events in the North Atlantic. The matching features between our SST record and the one from core MD97-2120 (southwest Pacific) suggests that the super-regional expression of climatic events is substantially affected by a single climatic agent: the Subtropical Front, amplifier and vehicle for the transfer of climatic change. The direct correlation between warmerDTsite at Vostok and warmer SST at ODP Site 1089 suggests that warmer oceanic/atmospheric conditions imply a more southward placed frontal system, weaker gradients, and therefore stronger Agulhas input to the Atlantic Ocean.