AGW Observer

Observations of anthropogenic global warming

Papers on permanent El Niño

Posted by Ari Jokimäki on August 31, 2011

This is a list of papers on permanent El Niño-like conditions. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Pliocene (5-3 Ma)

Implications of the permanent El Niño teleconnection “blueprint” for past global and North American hydroclimatology – Goldner et al. (2011) “Substantial evidence exists for wetter-than-modern continental conditions in North America during the pre-Quaternary warm climate intervals. This is in apparent conflict with the robust global prediction for future climate change of a northward expansion of the subtropical dry zones that should drive aridification of many semiarid regions. Indeed, areas of expected future aridification include much of western North America, where extensive paleoenvironmental records are documented to have been much wetter before the onset of Quaternary ice ages. It has also been proposed that climates previous to the Quaternary may have been characterized as being in a state with warmer-than-modern eastern equatorial sea surface temperatures (SSTs). Because equatorial Pacific SSTs exert strong controls on midlatitude atmospheric circulation and the global hydrologic cycle, the teleconnected response from this permanent El Niño-like mean state has been proposed as a useful analogue model, or “blueprint”, for understanding global climatological anomalies in the past. The present study quantitatively explores the implications of this blueprint for past climates with a specific focus on the Miocene and Pliocene, using a global climate model (CAM3.0) and a nested high-resolution climate model (RegCM3) to study the hydrologic impacts on global and North American climate of a change in mean SSTs resembling that which occurs during modern El Niño events. We find that the global circulation response to a permanent El Niño resembles a large, long El Niño event. This state also exhibits equatorial super-rotation, which would represent a fundamental change to the tropical circulations. We also find a southward shift in winter storm tracks in the Pacific and Atlantic, which affects precipitation and temperature over the mid-latitudes. In addition, summertime precipitation increases over the majority of the continental United States. These increases in precipitation are controlled by shifts in the subtropical jet and secondary atmospheric feedbacks. Based on these results and the data proxy comparison, we conclude that a permanent El Niño like state is one potential explanation of wetter-than-modern conditions observed in paleoclimate-proxy records, particularly over the western United States.” Goldner, A., Huber, M., Diffenbaugh, N., and Caballero, R.: Clim. Past, 7, 723-743, doi:10.5194/cp-7-723-2011, 2011. [Full text]

Teleconnections in a warmer climate: the pliocene perspective – Shukla et al. (2011) “Migrations toward altered sea surface temperature (SST) patterns in the Indo-Pacific region are present in the recent observational record and in future global warming projections. These SSTs are in the form of “permanent” El Niño-like (herein termed “El Padre”) and Indian Ocean Dipole (IOD)-like patterns. The Early Pliocene Warm Period, which bears similarity to future warming projections, may have also exhibited these Indo-Pacific SST patterns, as suggested by regional terrestrial paleo-climatic data and general circulation model studies. The ability to corroborate this assessment with paleo-data reconstructions is an advantage of the warm Pliocene period that is not afforded by future warming scenarios. Thus, the Pliocene period provides us with a warm-climate perspective and test bed for understanding potential changes to future atmospheric interactions given these altered SST states. This study specifically assesses how atmospheric teleconnections from El Padre/IOD SST patterns are generated and propagate to create the regional climate signals of the Pliocene period, as these signals may be representative of future regional climatic changes as well. To do this, we construct a holistic diagnostic rubric that allows us to examine atmospheric teleconnections, both energetically and dynamically, as produced by a general circulation model. We incorporate KE′, a diagnostic adapted from the eddy kinetic energy generation field, to assess the available energy transferred to these teleconnections. Using this methodology, we found that relative to our Modern Control experiments, weaker atmospheric teleconnections prevail under warm Pliocene conditions, although pathways of propagation still appear directed toward the southwestern United States from our tropical Pacific sector forcing. Propagation directly emanating from the Indian Ocean forcing sector appears to be largely blocked, although indirect teleconnective pathways appear traversing the Asian continent toward the North Pacific. The changes in the atmospheric circulation of Indian Ocean region in response to the underlying specified SST forcing (and indicated by Pliocene paleo-data) may have a host of implications for energy transfer out of and into the region, including interactions with the Asian jet stream and changes to the seasonal monsoon cycle. These interactions warrant further study in both past and future warm climate scenarios.” Sonali P. Shukla, Mark A. Chandler, David Rind, Linda E. Sohl, Jeff Jonas and Jean Lerner, Climate Dynamics, DOI: 10.1007/s00382-010-0976-y.

Permanent El Niño and the onset of Northern Hemisphere glaciations: Mechanism and comparison with other hypotheses – Vizcaíno et al. (2010) “The tropical Pacific transitioned from a “permanent El Niño” state, that is, without the current equatorial zonal gradient of sea surface temperatures, to one with an equatorial cold tongue in a process that started ∼4 Ma, during the early Pliocene. The latter stages of this transition, around ∼2.75 Ma, marked the onset of Northern Hemisphere glaciations. We explore the hypothesis that this onset of glaciation is causally linked to the development of the cold tongue guided by atmosphere general circulation model (AGCM) simulations forced by various hypothesized climate influences. A unique feature of our simulations is imposing permanent El Niño conditions not by imposing sea surface temperatures anomalies directly but rather through changing the implied ocean heat transport in the slab ocean component of the AGCM, done in such a way as to maintain global ocean heat balance. Similar to previous studies, we find increased near-surface temperature conditions occur during simulated permanent El Niño conditions at the locations of known ice sheet growth during glacial periods. We establish that this tropical-extratropical connection is mediated through atmospheric stationary waves, a well-known atmospheric pathway for today’s El Niño influence on North America. The influence of the permanent El Niño condition is compared, through model simulations, to other mechanisms proposed to date to explain the onset of glaciations at ∼2.75 Ma: changes in atmospheric carbon dioxide (CO2) concentrations, closure of the Panama seaway, and changes in North Pacific seasonality. The exact comparison is done by calculating differences in the equilibrium line altitude at the known locations of ice sheet growth, an approach that permits the translation of climate anomalies into a measurement of glaciation trends in terms of glacier mass balance. We find that permanent El Niño and atmospheric CO2 are the leading influences in this comparison, leading us to conjecture that the two influences combined determined the long-term background conditions governing ice sheet growth. Within this long-term background evolution, however, we additionally find that the exact timing of Northern Hemisphere glaciations is likely to have come from favorable orbital conditions. Our results regarding permanent El Niño on Northern Hemisphere glaciations is, however, conditioned on a strong sensitivity of Northern Hemisphere climate changes to how the oceanic heat compensation to the permanent El Niño is achieved.” Vizcaíno, M., S. Rupper, and J. C. H. Chiang (2010), Paleoceanography, 25, PA2205, doi:10.1029/2009PA001733. [Full text]

Tropical cyclones and permanent El Niño in the early Pliocene epoch – Fedorov et al. (2010) “Tropical cyclones (also known as hurricanes and typhoons) are now believed to be an important component of the Earth’s climate system. In particular, by vigorously mixing the upper ocean, they can affect the ocean’s heat uptake, poleward heat transport, and hence global temperatures. Changes in the distribution and frequency of tropical cyclones could therefore become an important element of the climate response to global warming. A potential analogue to modern greenhouse conditions, the climate of the early Pliocene epoch (approximately 5 to 3 million years ago) can provide important clues to this response. Here we describe a positive feedback between hurricanes and the upper-ocean circulation in the tropical Pacific Ocean that may have been essential for maintaining warm, El Niño-like conditions during the early Pliocene. This feedback is based on the ability of hurricanes to warm water parcels that travel towards the Equator at shallow depths and then resurface in the eastern equatorial Pacific as part of the ocean’s wind-driven circulation. In the present climate, very few hurricane tracks intersect the parcel trajectories; consequently, there is little heat exchange between waters at such depths and the surface. More frequent and/or stronger hurricanes in the central Pacific imply greater heating of the parcels, warmer temperatures in the eastern equatorial Pacific, warmer tropics and, in turn, even more hurricanes. Using a downscaling hurricane model, we show dramatic shifts in the tropical cyclone distribution for the early Pliocene that favour this feedback. Further calculations with a coupled climate model support our conclusions. The proposed feedback should be relevant to past equable climates and potentially to contemporary climate change.” Alexey V. Fedorov, Christopher M. Brierley & Kerry Emanuel, Nature 463, 1066-1070 (25 February 2010) | doi:10.1038/nature08831. [Full text]

Impact of a permanent El Niño (El Padre) and Indian Ocean Dipole in warm Pliocene climates – Shukla et al. (2009) “Pliocene sea surface temperature data, as well as terrestrial precipitation and temperature proxies, indicate warmer than modern conditions in the eastern equatorial Pacific and imply permanent El Niño–like conditions with impacts similar to those of the 1997/1998 El Niño event. Here we use a general circulation model to examine the global-scale effects that result from imposing warm tropical sea surface temperature (SST) anomalies in both modern and Pliocene simulations. Observed SSTs from the 1997/1998 El Niño event were used for the anomalies and incorporate Pacific warming as well as a prominent Indian Ocean Dipole event. Both the permanent El Niño (also called El Padre) and Indian Ocean Dipole (IOD) conditions are necessary to reproduce temperature and precipitation patterns consistent with the global distribution of Pliocene proxy data. These patterns may result from the poleward propagation of planetary waves from the strong convection centers associated with the El Niño and IOD.” Shukla, S. P., M. A. Chandler, J. Jonas, L. E. Sohl, K. Mankoff, and H. Dowsett (2009), Paleoceanography, 24, PA2221, doi:10.1029/2008PA001682. [Full text]

Greatly Expanded Tropical Warm Pool and Weakened Hadley Circulation in the Early Pliocene – Brierley et al. (2009) “The Pliocene warm interval has been difficult to explain. We reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago, during the early Pliocene. Our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced, implying a vast poleward expansion of the ocean tropical warm pool. Corroborating evidence indicates that the Pacific temperature contrast between the equator and 32°N has evolved from ∼2°C 4 million years ago to ∼8°C today. The meridional warm pool expansion evidently had enormous impacts on the Pliocene climate, including a slowdown of the atmospheric Hadley circulation and El Niño–like conditions in the equatorial region. Ultimately, sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake (such as enhanced ocean vertical mixing).” Chris M. Brierley, Alexey V. Fedorov, Zhonghui Liu, Timothy D. Herbert, Kira T. Lawrence and Jonathan P. LaRiviere, Science 27 March 2009: Vol. 323 no. 5922 pp. 1714-1718, DOI: 10.1126/science.1167625. [Full text]

Warm-water mollusc assemblages from northern Chile (Mejillones Peninsula): new evidence for permanent El Niño-like conditions during Pliocene warmth? – Ragaini et al. (2008) “Although results have been controversial, understanding the tropical Pacific climatic state during the Pliocene warm interval (c. 4.5–3.0 Ma) is crucial if insight is to be gained into the dynamic processes of present and future global warming. In the multi-proxy effort to reconstruct ancient climates, a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature-sensitive marine molluscs. Shallow-water strata of the Mejillones Peninsula, northern Chile (23°S), contain dense faunal assemblages in which molluscs exclusive to, or characteristic of, Pliocene deposits (Chlamys simpsoni, Chlamys vidali, Chorus blainvillei, Concholepas nodosa, Fusinus remondi, Herminespina mirabilis) coexist with surprisingly abundant and varied populations of extant warm-water species (Bulla punctulata, Cerithium stercusmuscarum, Olivella sp., Turbo cf. fluctuosus, Anomia peruviana, Argopecten ventricosus, Donax peruvianus, Dosinia ponderosa, Mexicardia procera, Undulostrea megodon), most of which have their current southern zoogeographical limit at 6°S. These tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that sea surface temperatures (SST) along the northern Chile coast were at least 2 °C warmer in the mid-Pliocene than at present, and that these very different conditions lasted long enough to allow stable colonization of the area. Such a significantly warmer SST pattern strongly resembles general climatic conditions accompanying modern El Niño events, when warm tropical waters propagate southward along the western margin of South America; this supports the existence in this area of persistently El Niño-like conditions during the mid-Pliocene.” Luca Ragaini, Claudio Di Celma and Gino Cantalamessa, Journal of the Geological Society; December 2008; v. 165; no. 6; p. 1075-1084; DOI: 10.1144/0016-76492007-039.

A permanent El Niño–like state during the Pliocene? – Haywood et al. (2007) “The Pliocene may have been characterized by permanent El Niño–like conditions. Initial modeling studies suggest that this may have contributed to Pliocene warmth. The termination of this state may have influenced Northern Hemisphere glaciation (NHG). We use the Hadley Centre Coupled Model version 3 to examine the role of the oceans and ocean structure on Pliocene warmth. A permanent El Niño–like state is not predicted. Annual mean sea surface temperatures in the eastern equatorial Pacific at Ocean Drilling Program Sites 847 and 851 increase by 1.71°C and 1.15°C, respectively. However, El Niño Southern Oscillation events are clearly expressed by the model. Sensitivity tests indicate that a prescribed permanent El Niño–like condition increases annual global mean surface temperatures by a maximum of 0.6°C. If the Pliocene was characterized by such a condition, it is questionable that it provided a major contribution to global warmth and therefore unlikely that the termination of this state contributed significantly to the onset of NHG.” Haywood, A. M., P. J. Valdes, and V. L. Peck (2007), Paleoceanography, 22, PA1213, doi:10.1029/2006PA001323. [Full text]

Early Pliocene (pre–Ice Age) El Niño–like global climate: Which El Niño? – Molnar & Cane (2011) “Paleoceanographic data from sites near the equator in the eastern and western Pacific Ocean show that sea-surface temperatures, and apparently also the depth and temperature distribution in the thermocline, have changed markedly over the past ∼4 m.y., from those resembling an El Niño state before ice sheets formed in the Northern Hemisphere to the present-day marked contrast between the eastern and western tropical Pacific. In addition, differences between late Miocene to early Pliocene (pre–Ice Age) paleoclimates and present-day average climates, particularly in the Western Hemisphere, resemble those associated with teleconnections from El Niño events, consistent with the image of a permanent El Niño state. Agreement is imperfect in that many differences between early Pliocene and present-day climates of parts of Africa, Asia, and Australia do not resemble the anomalies associated with canonical El Niño teleconnections. The teleconnections associated with the largest El Niño event in the past 100 yr, that in 1997–1998, do, however, reveal similar patterns of warming and the same sense, if not magnitude, of precipitation anomalies shown by differences between late Miocene-early Pliocene paleoclimates and present-day mean climates in these regions. If less consistent than those for the 1997–1998 event, temperature and precipitation anomalies correlated with the Pacific Decadal Oscillation also mimic many differences between early Pliocene and present-day climates. These similarities suggest that the sea-surface temperature distribution in the Pacific Ocean before Ice Age time resembled most that of the 1997–1998 El Niño, with the warmest region extending into the easternmost Pacific Ocean, not near the dateline as occurs in most El Niño events. This inference is consistent with equatorial Pacific proxy data indicating that at most a small east-west gradient in sea-surface temperature seems to have existed along the equator in late Miocene to early Pliocene time. Accordingly, such a difference in sea-surface temperatures may account for the large global differences in climate that characterized the earth before ice sheets became frequent visitors to the Northern Hemisphere.” Peter Molnar and Mark A. Cane, Geosphere, v. 3 no. 5 p. 337-365, doi: 10.1130/GES00103.1.

Warm upwelling regions in the Pliocene warm period – Dekens et al. (2007) “Given the importance of upwelling processes to coastal productivity and regional climate, it is critical to study the role of upwelling regions within the context of global climate change. We generated sea surface temperature (SST) records for the last 5 million years in three important upwelling regions: the eastern equatorial Pacific, the California margin, and the Peru margin. Prior to ∼3.0 Ma, SSTs at all sites were significantly warmer than today (by 3–9°C), indicating that cold upwelling regions that characterize the modern Pacific Ocean did not exist in the early Pliocene warm period (4.6 to 3.1 Ma), Earth’s most recent period of sustained global warmth. Alkenone, phosphorus, and organic carbon mass accumulation rate records indicate that changes in productivity and SST were decoupled and that upwelling of nutrient enriched water occurred even when SSTs were warm during the early Pliocene. Thus the long-term trends in SST are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling-favorable winds alone. The fact that gradual cooling of upwelling regions began before the onset of significant Northern Hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions. Our results suggest that the long-term average SSTs of upwelling regions are influenced by global changes in the depth and/or temperature of the ventilated thermocline.” Dekens, P. S., A. C. Ravelo, and M. D. McCarthy (2007), Paleoceanography, 22, PA3211, doi:10.1029/2006PA001394.

The Pliocene Paradox (Mechanisms for a Permanent El Niño) – Fedorov et al. (2006) “During the early Pliocene, 5 to 3 million years ago, globally averaged temperatures were substantially higher than they are today, even though the external factors that determine climate were essentially the same. In the tropics, El Niño was continual (or “permanent”) rather than intermittent. The appearance of northern continental glaciers, and of cold surface waters in oceanic upwelling zones in low latitudes (both coastal and equatorial), signaled the termination of those warm climate conditions and the end of permanent El Niño. This led to the amplification of obliquity (but not precession) cycles in equatorial sea surface temperatures and in global ice volume, with the former leading the latter by several thousand years. A possible explanation is that the gradual shoaling of the oceanic thermocline reached a threshold around 3 million years ago, when the winds started bringing cold waters to the surface in low latitudes. This introduced feedbacks involving ocean-atmosphere interactions that, along with ice-albedo feedbacks, amplified obliquity cycles. A future melting of glaciers, changes in the hydrological cycle, and a deepening of the thermocline could restore the warm conditions of the early Pliocene.” A. V. Fedorov, P. S. Dekens, M. McCarthy, A. C. Ravelo, P. B. deMenocal, M. Barreiro, R. C. Pacanowski and S. G. Philander, Science 9 June 2006: Vol. 312 no. 5779 pp. 1485-1489, DOI: 10.1126/science.1122666.

Cool La Niña During the Warmth of the Pliocene? – Rickaby & Halloran (2005) “The role of El Niño–Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niña–like state, rather than the proposed persistent warm El Niño–like conditions. Our Pliocene paleothermometer supports the idea of a dynamic “ocean thermostat” in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Niña–like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.” R. E. M. Rickaby and P. Halloran, Science 25 March 2005: Vol. 307 no. 5717 pp. 1948-1952, DOI: 10.1126/science.1104666. [Full text]

Permanent El Niño-Like Conditions During the Pliocene Warm Period – Wara et al. (2005) “During the warm early Pliocene (∼4.5 to 3.0 million years ago), the most recent interval with a climate warmer than today, the eastern Pacific thermocline was deep and the average west-to-east sea surface temperature difference across the equatorial Pacific was only 1.5 ± 0.9°C, much like it is during a modern El Niño event. Thus, the modern strong sea surface temperature gradient across the equatorial Pacific is not a stable and permanent feature. Sustained El Niño-like conditions, including relatively weak zonal atmospheric (Walker) circulation, could be a consequence of, and play an important role in determining, global warmth.” Michael W. Wara, Ana Christina Ravelo and Margaret L. Delaney, Science 29 July 2005: Vol. 309 no. 5735 pp. 758-761, DOI: 10.1126/science.1112596. [Full text]

Regional climate shifts caused by gradual global cooling in the Pliocene epoch – Ravelo et al. (2004) “The Earth’s climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 °C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. Tectonic changes and their influence on ocean heat transport have been suggested as forcing factors for that transition, including the onset of significant Northern Hemisphere glaciation ~2.75 million years ago, but the ultimate causes for the climatic changes are still under debate. Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago. Our results suggest that mean low-latitude climate conditions can significantly influence global climate feedbacks.” Ana Christina Ravelo, Dyke H. Andreasen, Mitchell Lyle, Annette Olivarez Lyle & Michael W. Wara, Nature 429, 263-267 (20 May 2004) | doi:10.1038/nature02567. [Full text]

Role of tropics in changing the response to Milankovich forcing some three million years ago – Philander & Fedorov (2003) “Throughout the Cenozoic the Earth experienced global cooling that led to the appearance of continental glaciers in high northern latitudes around 3 Ma ago. At approximately the same time, cold surface waters first appeared in regions that today have intense oceanic upwelling: the eastern equatorial Pacific and the coastal zones of southwestern Africa and California. There was furthermore a significant change in the Earth’s response to Milankovich forcing: obliquity signals became large, but those associated with precession and eccentricity remained the same. The latter change in the Earth’s response can be explained by hypothesizing that the global cooling during the Cenozoic affected the thermal structure of the ocean; it caused a gradual shoaling of the thermocline. Around 3 Ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions. This brought into play feedbacks involving ocean-atmosphere interactions of the type associated with El Niño and also mechanisms by which high-latitude surface conditions can influence the depth of the tropical thermocline. Those feedbacks and mechanisms can account for the amplification of the Earth’s response to periodic variations in obliquity (at a period of 41K) without altering the response to Milankovich forcing at periods of 100,000 and 23,000 years. This hypothesis is testable. If correct, then in the tropics and subtropics the response to obliquity variations is in phase with, and corresponds to, El Niño conditions when tilt is large and La Niña conditions when tilt is small.” Philander, S. G., and A. V. Fedorov (2003), Paleoceanography, 18(2), 1045, doi:10.1029/2002PA000837. [Full text]

Eocene (55-35 Ma)

El Niño in the Eocene greenhouse recorded by fossil bivalves and wood from Antarctica – Ivany et al. (2011) “Quasi-periodic variation in sea-surface temperature, precipitation, and sea-level pressure in the equatorial Pacific known as the El Niño – Southern Oscillation (ENSO) is an important mode of interannual variability in global climate. A collapse of the tropical Pacific onto a state resembling a so-called ‘permanent El Niño’, with a preferentially warmed eastern equatorial Pacific, flatter thermocline, and reduced interannual variability, in a warmer world is predicted by prevailing ENSO theory. If correct, future warming will be accompanied by a shift toward persistent conditions resembling El Niño years today, with major implications for global hydrological cycles and consequent impacts on socioeconomic and ecological systems. However, much uncertainty remains about how interannual variability will be affected. Here, we present multi-annual records of climate derived from growth increment widths in fossil bivalves and co-occurring driftwood from the Antarctic peninsula that demonstrate significant variability in the quasi-biennial and 3–6 year bands consistent with ENSO, despite early Eocene (∼50 Mya) greenhouse conditions with global average temperature ∼10 degrees higher than today. A coupled climate model suggests an ENSO signal and teleconnections to this region during the Eocene, much like today. The presence of ENSO variation during this markedly warmer interval argues for the persistence of robust interannual variability in our future greenhouse world.” Ivany, L. C., T. Brey, M. Huber, D. P. Buick, and B. R. Schöne (2011), Geophys. Res. Lett., 38, L16709, doi:10.1029/2011GL048635.

Eocene El Niño: Evidence for Robust Tropical Dynamics in the “Hothouse” – Huber & Caballero (2003) “Much uncertainty surrounds the interactions between the El Niño–Southern Oscillation (ENSO) and long-term global change. Past periods of extreme global warmth, exemplified by the Eocene (55 to 35 million years ago), provide a good testing ground for theories for this interaction. Here, we compare Eocene coupled climate model simulations with annually resolved variability records preserved in lake sediments. The simulations show Pacific deep-ocean and high-latitude surface warming of ∼10°C but little change in the tropical thermocline structure, atmosphere-ocean dynamics, and ENSO, in agreement with proxies. This result contrasts with theories linking past and future “hothouse” climates with a shift toward a permanent El Niño–like state.” Matthew Huber and Rodrigo Caballero, Science 7 February 2003: Vol. 299 no. 5608 pp. 877-881, DOI: 10.1126/science.1078766. [Full text]

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