Environmental information in the isotopic record in trees

1990 ◽  
Vol 330 (1615) ◽  
pp. 427-439 ◽  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Environmental Information ◽  
Anthropogenic Effect ◽  
Geographic Locations ◽  
The Past ◽  
Past 1000 Years

Twenty-three trees from widely different geographic locations and different environments were analysed for the 8D and 8 13 C records. The 8D values suggested that the temperature of the Earth’s surface rose over the past 100 years and probably for the past 1000 years. The rate of warming appears to be latitude dependent, greatest in the cooler areas. The 8 13 C record, obtained for seven of the 23 trees, contain the 8 13 C decrease due to the anthropogenic effect, the addition of CO 2 from coal and petroleum burning. This effect appears to be twice as high in the Northern Hemisphere as in the Southern Hemisphere.

Extra-tropical Northern Hemisphere land temperature variability over the past 1000 years

2004 ◽  
Vol 23 (20-22) ◽  
pp. 2063-2074 ◽  
Author(s):  
Edward R. Cook ◽  
Jan Esper ◽  
Rosanne D. D’Arrigo
Keyword(s):  
Northern Hemisphere ◽  
Temperature Variability ◽  
The Past ◽  
Past 1000 Years

scholarly journals Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

2017 ◽  
Vol 17 (21) ◽  
pp. 13373-13389 ◽  
Author(s):  
Margarita Yela ◽  
Manuel Gil-Ojeda ◽  
Mónica Navarro-Comas ◽  
David Gonzalez-Bartolomé ◽  
Olga Puentedura ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Hemispheric Asymmetry ◽  
Polar Vortex ◽  
N2o Decomposition ◽  
Atmospheric Composition ◽  
Vertical Column ◽  
The Past ◽  
Vertical Column Density ◽  
Decadal Trend

Abstract. Over 20 years of stratospheric NO2 vertical column density (VCD) data from ground-based zenith DOAS spectrometers were used for trend analysis, specifically, via multiple linear regression. Spectrometers from the Network for the Detection of Atmospheric Composition Change (NDACC) cover the subtropical latitudes in the Northern Hemisphere (Izaña, 28° N), the southern Subantarctic (Ushuaia, 55° S) and Antarctica (Marambio, 64° S, and Belgrano, 78° S). The results show that for the period 1993–2014, a mean positive decadal trend of +8.7 % was found in the subtropical Northern Hemisphere stations, and negative decadal trends of −8.7 and −13.8 % were found in the Southern Hemisphere at Ushuaia and Marambio, respectively; all trends are statistically significant at 95 %. Belgrano only shows a significant decadal trend of −11.3 % in the summer/autumn period. Most of the trends result from variations after 2005. The trend in the diurnal build-up per hour (DBU) was used to estimate the change in the rate of N2O5 conversion to NO2 during the day. With minor differences, the results reproduce those obtained for NO2. The trends computed for individual months show large month-to-month variability. At Izaña, the maximum occurs in December (+13.1 %), dropping abruptly to lower values in the first part of the year. In the Southern Hemisphere, the polar vortex dominates the monthly distributions of the trends. At Marambio, the maximum occurs in mid-winter (−21 %), whereas at the same time, the Ushuaia trend is close to its annual minimum (−7 %). The large difference in the trends at these two relatively close stations suggests a vortex shift towards the Atlantic/South American area over the past few years. Finally, the hemispheric asymmetry obtained in this work is discussed in the framework of the results obtained by previous works that considered tracer analysis and Brewer–Dobson circulation. The results obtained here provide evidence that the NO2 produced by N2O decomposition is not the only cause of the observed trend in the stratosphere and support recent publications pointing to a dynamical redistribution starting in the past decade.

Recent Stratospheric Climate Trends as Evidenced in Radiosonde Data: Global Structure and Tropospheric Linkages

2005 ◽  
Vol 18 (22) ◽  
pp. 4785-4795 ◽  
Author(s):  
David W. J. Thompson ◽  
Susan Solomon
Keyword(s):  
Radiative Transfer ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Global Structure ◽  
Current Understanding ◽  
Radiosonde Data ◽  
Climate Trends ◽  
The Past ◽  
Stratospheric Temperature ◽  
Temperature Trends

Abstract The global structure of recent stratospheric climate trends is examined in radiosonde data. In contrast to conclusions published in previous assessments of stratospheric temperature trends, it is demonstrated that in the annual mean the tropical stratosphere has cooled substantially over the past few decades. The cooling of the tropical stratosphere is apparent in both nighttime and adjusted radiosonde data, and seems to be robust to changes in radiosonde instrumentation. The meridional structure of the annual-mean stratospheric trends is not consistent with our current understanding of radiative transfer and constituent trends but is consistent with increased upwelling in the tropical stratosphere. The annual-mean cooling of the tropical stratosphere is juxtaposed against seasonally varying trends in the extratropical stratosphere dominated by the well-known springtime cooling at polar latitudes. The polar stratospheric trends are accompanied by similarly signed trends at tropospheric levels in the Southern Hemisphere but not in the Northern Hemisphere.

scholarly journals Observations of the anisotropy of cosmic rays at TeV&#8211;PeV

2014 ◽  
Vol 1 ◽  
pp. 33-37 ◽  
Author(s):  
S. BenZvi
Keyword(s):  
Cosmic Rays ◽  
High Altitude ◽  
Southern Hemisphere ◽  
Energy Dependence ◽  
Northern Hemisphere ◽  
Energy Band ◽  
The Past ◽  
Small Scales ◽  
Northern And Southern Hemispheres

Abstract. During the past decade, multiple observatories have reported significant observations of the anisotropy of cosmic rays in the TeV energy band. The anisotropy has been observed at large scales and small scales in both the Northern and Southern Hemispheres. The source of the anisotropy is not well-understood, though both a galactic and a heliospheric origin have been suggested. We discuss recent observations of the shape and energy dependence of the anisotropy, with particular attention to measurements by the IceCube Neutrino Observatory in the Southern Hemisphere and the Milagro and High-Altitude Water Cherenkov (HAWC) observatories in the Northern Hemisphere.

scholarly journals Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years 

2021 ◽  
Author(s):  
Aleix Cortina-Guerra ◽  
Juan José Gomez-Navarro ◽  
Belen Martrat ◽  
Juan Pedro Montávez ◽  
Alessandro Incarbona ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
Sea Surface ◽  
The West ◽  
The Past ◽  
Main Driver ◽  
Climate Model Simulations ◽  
Past 1000 Years

Abstract. High resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lions was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mb in the Northern Hemisphere (200 N-900 N and 1000 W-800 E). Correlations revealed a pattern similar to the Eastern Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 yr of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone Sea Surface Temperature (SST) reconstructions that documented an increase in the west-east basin gradients during EMT-type events.

scholarly journals Absence of a Medieval Climate Anomaly, Little Ice Age and twentieth century warming in Skarvsnes, Lützow Holm Bay, East Antarctica

2014 ◽  
Vol 26 (5) ◽  
pp. 585-598 ◽  
Author(s):  
Ines Tavernier ◽  
Elie Verleyen ◽  
Dominic A. Hodgson ◽  
Katrien Heirman ◽  
Stephen J. Roberts ◽  
...  
Keyword(s):  
Twentieth Century ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Little Ice Age ◽  
Environmental Changes ◽  
Open Water ◽  
Ice Age ◽  
Medieval Climate Anomaly ◽  
Climate Anomaly ◽  
The Past

AbstractPalaeoclimate changes, such as the Medieval Climate Anomaly and the Little Ice Age, are well-defined in the Northern Hemisphere during the past 2000 years. In contrast, these anomalies appear to be either absent, or less well-defined, in high-latitude regions of the Southern Hemisphere. Here, we inferred environmental changes during the past two millennia from proxies in a sediment core from Mago Ike, an East Antarctic lake in Skarvsnes (Lützow Holm Bay). Variations in lake primary production were inferred from fossil pigments, sedimentological and geochemical proxies and combined with absolute diatom counts to infer past diatom productivity and community changes. Three distinct stratigraphic zones were recognized, resulting from a shift from marine to lacustrine conditions with a clear transition zone in between. The presence of open-water marine diatoms indicates a coastal zone seasonally free of sea ice between c. 2120–1500 cal yr bp. Subsequently, the lake became isolated from the ocean due to isostatic uplift. Freshwater conditions were established from c. 1120 cal yr bp onwards after which the proxies are considered highly sensitive to temperature changes. There is no evidence for a Medieval Climate Anomaly, Little Ice Age or twentieth century warming in our lake sediment record suggesting that studies that have imposed Northern Hemisphere climate anomalies onto Southern Hemisphere palaeoclimate records should be treated with caution.

scholarly journals Recent warming inconsistent with natural association between temperature and atmospheric circulation over the last 2000 years

2006 ◽  
Vol 2 (3) ◽  
pp. 327-355 ◽  
Author(s):  
P. A. Mayewski ◽  
K. A. Maasch
Keyword(s):  
Climate Variability ◽  
Atmospheric Circulation ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
High Latitude ◽  
Natural Climate Variability ◽  
The Past ◽  
Past 2000 Years ◽  
Hemisphere Temperature ◽  
Natural Climate

Abstract. Comparison between proxies for atmospheric circulation and temperature reveals associations over the last few decades that are inconsistent with those of the past 2000 years. Notably, patterns of middle to high latitude atmospheric circulation in both hemispheres are still within the range of variability of the last 6–10 centuries while, as demonstrated by Mann and Jones (2003), Northern Hemisphere temperatures over recent decades are the highest of the last 2000 years. Further, recent temperature change precedes change in middle to high latitude atmospheric circulation unlike the two most notable changes in climate of the past 2000 years during which change in atmospheric circulation preceded or coincided with change in temperature. In addition, the most prominent change in Southern Hemisphere temperature and atmospheric circulation of the past 2000, and probably 9000 years, precedes change in temperature and atmospheric circulation in the Northern Hemisphere unlike the recent change in Northern Hemisphere temperature that leads. These findings provide new verification that recent rise in temperature is inconsistent with natural climate variability and is most likely related to anthropogenic activity in the form of enhanced greenhouse gases. From our investigation we conclude that the delayed warming over much of the Southern Hemisphere may be, in addition to other factors, a consequence of underpinning by natural climate variability. Further bipolar comparison of proxy records of atmospheric circulation demonstrates that change in atmospheric circulation in the Southern Hemisphere led by 400 years, the most abrupt change in Northern Hemisphere atmospheric circulation of the last 9000 years. This finding may be highly relevant to understanding a future when warming becomes more fully established in the Southern Hemisphere.

scholarly journals Aspectos de la historia de la vegetación de México con base en macrofósiles de angiospermas

2017 ◽  
pp. 99
Author(s):  
Sergio R.S. Cevallos-Ferriz ◽  
Alicia Silva-Pineda
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Phylogenetic Relationships ◽  
Endemic Plants ◽  
Vegetation Types ◽  
The Past ◽  
Long Time ◽  
History Of ◽  
Work Done ◽  
The Relationship

The history of Mexican vegetation is mainly known through extrapolations based on its extant flora and/or paleobotanical work done in other countries. While macrofossils corroborate that in the past, as in the present, the Mexican flora had relationships with those of other areas, its study reveals that during the Cretaceous it had affinities with the boreal floras, though, some of the d escribed plants have close phylogenetic relationships with plants now growing naturally in the southern hemisphere. During the Tertiary the relationship with the boreal floras continued, suggesting that if some taxa originated in Gondwana, at least some of their genera and species could differentiate and radiate in the northern hemisphere, as suggested by some Anacardiaceae and perhaps other Leguminosae. A legume, Lysiloma, suggest that endemic taxa that characterize the extant Mexican vegetation have a long history, since they are known from Oligocene sediments. Another plant of the same family, Reinweberia, also suggest that during the Tertiary there were endemic plants that became extinct, and underscores the fact that for a long time the Mexican vegetation have had a distinct composition. The macrofossils of angiosperms suggest that only recently, perhaps no more than 10 million years ago, the vegetation types recognized today were established, although, those of the past could be similar.

scholarly journals Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

2017 ◽  
Author(s):  
Margarita Yela ◽  
Manuel Gil-Ojeda ◽  
Mónica Navarro-Comas ◽  
David González-Bartolomé ◽  
Olga Puentedura ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Hemispheric Asymmetry ◽  
Polar Vortex ◽  
N2o Decomposition ◽  
Atmospheric Composition ◽  
Vertical Column ◽  
The Past ◽  
Vertical Column Density ◽  
Decadal Trend

Abstract. Over twenty years of stratospheric NO2 vertical column density (VCD) data from ground-based zenith DOAS spectrometers was used for trend analysis, specifically, via multiple linear regression. Spectrometers from the Network for the Detection of Atmospheric Composition Change (NDACC) cover the subtropical latitudes in the Northern Hemisphere (Izaña, 28° N), southern Subantarctica (Ushuaia, 55° S) and Antarctica (Marambio, 64° S and Belgrano, 78° S). The results show that for the period 1993–2014, a mean positive decadal trend of +8.7 % was found in the subtropical Northern Hemisphere stations, and negative decadal trends of −9.1 % and −13.8 % were found in the Southern Hemisphere at Ushuaia and Marambio, respectively; all trends are statistically significant at 95 %. Belgrano only shows a significant decadal trend of −11.3 % in the summer/autumn period. Most of the trends result from variations after 2005. The trend in the diurnal build up per hour (DBU) was used to estimate the change in the rate of N2O5 conversion to NO2 during the day. With minor differences, the results reproduce those obtained for NO2. The trends computed for individual months show large month-to-month variability. At Izaña, the maximum occurs in December (+13.1 %), dropping abruptly to lower values in the first part of the year. In the Southern Hemisphere, the polar vortex dominates the monthly distributions of the trends. At Marambio, the maximum occurs in the mid-winter (−21 %), whereas at the same time, the Ushuaia trend is close to its annual minimum (−7 %). The large difference in the trends at these two relatively close stations suggests a vortex shift towards the Atlantic/South American area over the past few years. Finally, the hemispheric asymmetry obtained in this work is discussed in the frame of the results obtained by previous works that considered tracer analysis and Brewer-Dobson circulation. The results obtained here provide evidence that the NO2 produced by N2O decomposition is not the only cause of the observed trend in the stratosphere and support recent publications pointing to a dynamical redistribution starting in the past decade.

scholarly journals Continental-scale temperature variability in PMIP3 simulations and PAGES 2k regional temperature reconstructions over the past millennium

2015 ◽  
Vol 11 (12) ◽  
pp. 1673-1699 ◽  
Author(s):  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Forced Response ◽  
The Arctic ◽  
Model Simulations ◽  
Continental Scale ◽  
The Past ◽  
External Forcings ◽  
Temperature Reconstructions ◽  
Past Millennium

Abstract. Estimated external radiative forcings, model results, and proxy-based climate reconstructions have been used over the past several decades to improve our understanding of the mechanisms underlying observed climate variability and change over the past millennium. Here, the recent set of temperature reconstructions at the continental-scale generated by the PAGES 2k project and a collection of state-of-the-art model simulations driven by realistic external forcings are jointly analysed. The first aim is to estimate the consistency between model results and reconstructions for each continental-scale region over the time and frequency domains. Secondly, the links between regions are investigated to determine whether reconstructed global-scale covariability patterns are similar to those identified in model simulations. The third aim is to assess the role of external forcings in the observed temperature variations. From a large set of analyses, we conclude that models are in relatively good agreement with temperature reconstructions for Northern Hemisphere regions, particularly in the Arctic. This is likely due to the relatively large amplitude of the externally forced response across northern and high-latitude regions, which results in a clearly detectable signature in both reconstructions and simulations. Conversely, models disagree strongly with the reconstructions in the Southern Hemisphere. Furthermore, the simulations are more regionally coherent than the reconstructions, perhaps due to an underestimation of the magnitude of internal variability in models or to an overestimation of the response to the external forcing in the Southern Hemisphere. Part of the disagreement might also reflect large uncertainties in the reconstructions, specifically in some Southern Hemisphere regions, which are based on fewer palaeoclimate records than in the Northern Hemisphere.

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