Climate variability

Climate and subsurface sea temperature in Bahía Culebra, Costa Rica

by Eric Alfaro

Alfaro, E., J. Cortés, J. Alvarado, C. Jiménez, C. Sánchez, J. Nivia, A. León y E. Ruiz, 2012. Clima y temperatura sub-superfical del mar en Bahía Culebra, Golfo de Papagayo, Costa Rica. Revista de Biología Tropical, 60(Supl. 2), 159-171.

Bahía Culebra, Golfo de
Papagayo, Costa Rica is a seasonal upwelling area. To determine the relationship of... more Bahía Culebra, Golfo de
Papagayo, Costa Rica is a seasonal upwelling area. To determine the relationship of climate and the subsurface
temperature variability at Bahía Culebra, we analyzed nine records of sea subsurface temperature from the Bay,
continuously recorded from 1998 to 2010. The analysis characterized the annual cycle and explored the influ-
ence of different climate variability sources on the subsurface sea temperature and air temperature recorded in
Bahía Culebra. Data from an automatic meteorological station in the bay were studied, obtaining the annual and
daily cycle for air surface temperature and wind speed. Sea surface temperature (SST) trend from 1854 to 2011
was calculated from reanalysis for the region that coverts 9-11°N, 85-87°W. Because of the positive SST trend
identified in this region, results showed that annual and daily cycles in Bahía Culebra should be studied under
a warming scenario since 1854, that is coherent with the global warming results and its climate variability is
influenced by El Niño-Southern Oscillation (ENSO) in the Equatorial Pacific and by atmospheric forcing trig-
gered by climate variability with Atlantic Ocean origin, because warm (cold) events in Bahía Culebra tend to
occur in concordance with positive & negative (negative & positive) anomalies in Niño 3.4 (NAO) index. Rev.
Biol. Trop. 60 (Suppl. 2): 159-171.

Wildfire activity in rainforests in western Patagonia linked to the Southern Annular Mode

by Andrés Holz

Fire history in western Patagonia from paired tree-ring fire-scar and charcoal records

by Andrés Holz

Non-linear cyclic regimes of short-term climate variability

by Perry Sih

Empirical assessment of state-and-transition models with a long-term vegetation record from the Sonoran Desert

by Sumanta Bagchi

Bagchi, Sumanta, David D. Briske, Xinyuan Ben Wu, Mitchel McClaran, Brandon Bestelmeyer, and Maria E. Fernandez-Gimenez. In press. Empirical assessment of state-and-transition models with a long-term vegetation record from the Sonoran Desert. Ecological Applications. [doi:10.1890/11-0704.1]

Resilience-based frameworks, including state-and-transition models (STM), are being increasingly called upon to inform... more Resilience-based frameworks, including state-and-transition models (STM), are being increasingly called upon to inform policy and guide ecosystem management, particularly in rangelands. Yet, multiple challenges impede their effective implementation – (1) paucity of empirical tests of resilience-concepts, such as alternative states and thresholds, and (2) heavy reliance on expert models, which are seldom tested against empirical data. We developed an analytical protocol to identify unique plant communities and their transitions, and applied it to a long-term vegetation record from the Sonoran Desert (1953-2009). We assessed whether empirical trends were consistent with resilience concepts, and evaluated how they may inform the construction and interpretation of expert STMs. Seven statistically distinct plant communities were identified based on the cover of 22 plant species in 68 permanent transects. We recorded 253 instances of community transitions, associated with changes in species composition between successive samplings. Expectedly, transitions were more frequent among proximate communities with similar species pools than among distant communities. But unexpectedly, communities and transitions were not strongly constrained by soil type and topography. Only 18 transitions featured disproportionately large compositional turnover (species dissimilarity between 0.54 and 0.68), and these were closely associated with communities that were dominated by the common shrub (burroweed, Haplopappus tenuisecta); indicating that only some, and not all, communities may be prone to large compositional change. Temporal dynamics in individual transects illustrated four general trajectories – stability, non-directional drift, reversibility, and directional shifts that were not reversed even after 2-3 decades. The frequency of transitions and the accompanying species dissimilarity were both positively correlated with fluctuation in precipitation, indicating that climatic drivers require more attention in STMs. Many features of the expert models, including the number of communities and participant species, were consistent with empirical trends, but expert models under-represented recent increases in cacti while over-emphasizing the introduced Lehmann’s lovegrass (Eragrostis lehmanniana). Quantification of communities and transitions within long-term vegetation records presents several quantitative metrics such as transition frequency, magnitude of accompanying compositional change, presence of uni-directional trajectories, and lack of reversibility within various time-scales, which can clarify resilience concepts and inform the construction and interpretation of STMs.

A global dynamic model for the Neolithic transition

by Carsten Lemmen

Co-authored with Kai W. Wirtz, published in Climatic Change 59, 333–367, 2003.

During the Holocene strong gradients in the distribution of technology including subsistence ways emerged on a global... more During the Holocene strong gradients in the distribution of technology including subsistence ways emerged on a global scale. These patterns were further amplified in historic times and are still visible through worldwide differences in national wealth. In order to evaluate major factors responsible for the shift from foraging to food production we here employ quantitative methods by developing a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP the inhabited world is split into 197 regions with homogeneous environmental conditions. Suitable variables for the macro-economic and cultural development in the Neolithic period are found to be farming to hunting-gathering ratio, number of agricultural economies and a technological development index. The model explicitly describes economic adaptation, growth and migration of human populations together with the spread of their cultural characteristics; it accounts for over- exploitation of natural resources, crowding mortality and the climate variability on a millennium scale. In a thorough model validation region specific trajectories are compared to archaeological evidence revealing a high correspondence. Major parts of the known sequence of Neolithic centers including the timing differences are robustly reproduced. A series of known problems in prehistory is discussed comprising the lag between domestication and full scale farming, the off-leveling of the technological boost following the transition, the emergence of distinct migration waves and sensitiv- ity to climate fluctuations. Not mere population pressure but continuous innovation and competition between subsistence strategies is identified as a prime mover of agricultural development. The results suggest that few aspects of biogeography may have determined the observed continental gradients in the number of domesticable species ultimately leading to an increasing differentiation in technology and demography.

An analysis of observed daily maximum wind gusts in the UK

by Richard Hewston

The greatest attention to the UK wind climatology has focused upon mean windspeeds, despite a knowledge of gust speeds... more The greatest attention to the UK wind climatology has focused upon mean windspeeds, despite a knowledge of gust speeds being essential to a variety of users. This paper goes some way to redressing this imbalance by analysing observed daily maximum gust speeds from a 43-station network over the period 1980–2005. Complementing these data are dynamically downscaled reanalysis data, generated using the PRECIS Regional Climate Modelling system, for the period 1959–2001. Inter-annual variations in both the observed and downscaled reanalysis gust speeds are presented, with a statistically significant (at the 95% confidence interval) 5% increase across the network in daily maximum gust speeds between 1959 and the early 1990s, followed by an apparent decrease. The benefit of incorporating dynamically downscaled reanalysis data is revealed by the fact that the decrease in gust speeds since 1993 may be placed in the context of a very slight increase displayed over the longer 1959–2001 period. Furthermore, the severity of individual windstorm events is considered, with high profile recent events placed into the context of the long term record. A daily cycle is identified from the station observations in the timing of the daily maximum gust speeds, with an afternoon peak occurring between 12:00–15:00, exhibiting spatial and intra-annual variations.

Modeling density dependence and climatic disturbances in caribou: a case study from the Bathurst Island complex, Canadian High Arctic

by Mike Ferguson

Tews J, Ferguson MAD, Fahrig L. 2007. Modeling density dependence and climatic disturbances in caribou: A case study from the Bathurst Island complex, Canadian high arctic. Journal of Zoology 272(2): 209-217.

Keywords: climate change; density independence; environmental stochasticity; Peary caribou; population dynamics; population viability analysis; simulation model

Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the... more Peary caribou Rangifer tarandus pearyi is the northernmost subspecies of Rangifer in North America and endemic to the Canadian High Arctic. Because of severe population declines following years of unfavorable winter weather with ice coating on the ground or thicker snow cover, it is believed that density-independent disturbance events are the primary driver for Peary caribou population dynamics. However, it is unclear to what extent density dependence may affect population dynamics of this species. Here, we test for different levels of density dependence in a stochastic, single-stage population model, based on available empirical information for the Bathurst Island complex (BIC) population in the Canadian High Arctic. We compare predicted densities with observed densities during 1961–2001 under various assumptions of the strength of density dependence. On the basis of our model, we found that scenarios with no or very low density dependence led to population densities far above observed densities. For average observed disturbance regimes, a carrying capacity of 0.1 caribou km−2 generated an average caribou density similar to that estimated for the BIC population over the past four decades. With our model we also tested the potential effects of climate change-related increases in the probability and severity of disturbance years, that is unusually poor winter conditions. On the basis of our simulation results, we found that, in particular, potential increases in disturbance severity (as opposed to disturbance frequency) may pose a considerable threat to the persistence of this species.

Analysis of evapotranspiration variability and trends in the Arabian Peninsula.

by Mohammad ElNesr

El-Nesr,M., A. Alazba and M. Abu-Zreig, 2010. Analysis of evapotranspiration variability and trends in the Arabian Peninsula. Am. J. Environ Sci., 6: 535-547. DOI: 10.3844/ajessp.2010.535.547

Problem statement: Climate variability is receiving much attention recently because it has significant effects on... more Problem statement: Climate variability is receiving much attention recently because it has significant effects on water resources and therefore on the livelihood of society especially in water scarce countries such the Kingdom of Saudi Arabia (KSA). Approach: The aim of this study was to explore changes in the reference evapotranspiration (ETo) using data from 27 weather stations through years 1980-2008 and to identify trend directions in the ETo as an indicator to climate variability in the region. ETo was calculated using FAO-56 Penman Monteith method and trends analyses were performed with non-parametric statistics proposed by Mann-Kendall and Sen slope estimator. Results: Results indicated that the average ETo varied from 5 mm day −1 in January to more than 15 mm day −1 in July with extreme average values ranged from 4 mm day−1 in January to 18 mm day−1 in July. The trend analyses indicated that the average annual maximum and minimum daily ETo steadily increased over the study period. The ETo annual daily average had increased from about 9.6 mm day−1 in 1980 to 10.5 mm day−1 in 2008. Trend analysis with Mann-Kendall and Sen Slope gave consistent results and were able to detect trend direction and its significant level for each month and for each station. In general, most of stations showed an increasing trend especially in the Northern parts of KSA and along the longitudinal line of 45°. ‘Yenbo’ station showed a significant increasing trend in ETo for the entire year. The increasing trends prevailed during most of the year except in the winter months from October to January. Even during these winter months, significant decreasing trends were observed for only four stations. Conclusion: It is recommended to perform similar studies on other parts of the Arabian Peninsula using wider databases, and to consider the increasing trend of ETo in the planning for agricultural and water resources projects.

Arctic tundra caribou and climatic change: Questions of temporal and spatial scales

by Mike Ferguson

Ferguson, M.A.D. 1996. Arctic tundra caribou and climatic change: Questions of temporal and spatial scales. Geoscience Canada 23: 245-252.

Climatic changes have affected populations of caribou and reindeer (Rangifer tarandus) at scales ranging from a single... more Climatic changes have affected populations of caribou and reindeer (Rangifer tarandus) at scales ranging from a single winter to tens of thousands of years, and from micro-habitats to entire continents. Individuals, populations and the species have adapted to these climatic changes, however, producing complex evolutionary and ecological issues requiring multi-scale, interdisciplinary research. Caribou populations wintering on arctic tundra may be most susceptible to the impacts of anthropogenic climatic change, given the low productivity of their forage, the severity and duration of the winters, and the physical barriers that limit dispersal.

Sub-speciation of Rangifer tarandus hypotheticaly occurred during the Wisconsin glaciation. Recent genetic analyses support the current classification of subspecies, except that Baffin Island caribou may be distinct from barren-ground caribou, R. t. groenlandicus, on mainland Northwest Territories. Baffin caribou may have originated from a small ancestral population in a refugium on Baffin Island during the Wisconsin glaciation; or, they may have originated from immigrants after the Wisconsin glaciation, later experiencing a severe population bottleneck.

On a shorter time scale, recent research has suggested that density-independent climatic events occurring over a single winter have caused at least one major population decline among Peary caribou on the Queen Elizabeth Islands. Dramatic fluctuations of Greenland populations over the past 200 years have been attributed to climatic changes. However, the onset of some population changes on western Greenland have been inconsistent with the timing of climatic changes. Inuit knowledge of Baffin caribou and studies of tundra caribou on Svalbard, Coats and Southampton islands, South Georgia, and Norway suggest that caribou populations are affected primarily by density-dependent grazing impacts on forage that can last several decades. The discrepancy between these views may be caused by differences in the temporal and spatial scales over which scientific investigations have been conducted, and the measurement of only some ecological factors. Arctic ecological studies require extensive spatial and temporal data before impacts of anthropogenic climate change can be assessed. This will require a long-term interdisciplinary study integrating scientific data from several disciplines, as well as Inuit knowledge.

Between Warm and Cold: Impact of the Younger Dryas on Human Behavior in Central Europe

by Sonja B. Grimm

Weber, M.-J., Grimm, S. B. & Baales, M. (2011): Between warm and cold - Impact of Dryas III on human behavior in Central Europe. Quaternary International 242, 277-301. (special issue: Straus, L. G. & Goebel, T. (eds.): Humans and Younger Dryas: Dead end, short detour, or open road to the Holocene? Proceedings of the symposium on Human Responses to Younger Dryas in the Northern Hemisphere at the 75th SAA annual meeting, April, 17th, St. Louis)

A PDF-copy of the article can be requested via email

Following a thorough review of high-resolution environmental archives, this paper aims at discriminating the factors... more Following a thorough review of high-resolution environmental archives, this paper aims at discriminating the factors determining the heterogeneous repercussion of the Lateglacial Younger Dryas in Central Europe. When examining the archaeological implications of human adaptation to the subsequent changes in the natural environment two divergent biotic regions are of special interest: the North European Plain and adjacent areas; and the Alpine foothills and surrounding mountain ranges. In these regions, two different archaeological technocomplexes (traditions) are found: the Tanged Point Complex and the Curve-Backed Point Groups. Considering the distribution of the archaeological sites witnessing changes in the material culture and subsistence pattern, the intensity of the environmental changes caused by the Younger Dryas is a decisive element. Settlement discontinuity during the Younger Dryas is questioned. Moreover, the potential existence of established social networks between the two regions expressed by comparable developments such as microlithization is considered. Finally, the authors assess whether the Younger Dryas acted as an accelerator or a brake in the process of regional diversification prior to the Early Mesolithic.

Impactos socio-ambientales de la variabilidad climática. Las sequías en Venezuela

by KARENIA CÓRDOVA SÁEZ

Resumen:
El impacto de la variabilidad climática sobre los factores socio-
ambientales; como el desarrollo... more Resumen:
El impacto de la variabilidad climática sobre los factores socio-
ambientales; como el desarrollo económico, el abastecimiento de agua potable,la salud y el bienestar social de la población en general, han ido en aumento en las últimas décadas del siglo XX y en el temprano siglo XXI, producto de la incertidumbre climática y el estado de emergencia ambiental, que las alteraciones climáticas han desencadenado en diversas regiones del globo. Estas evidencias son consecuencia de un proceso de cambio climático global agravado por el
aumento de las emisiones de gases de efecto invernadero, así como por la falta de compromiso en el control de estas emisiones por parte de los principales
responsables. Las expectativas socio-ambientales frente a estos escenarios de incertidumbre y riesgo, no son muy alentadoras. La gestión de los recursos prioritarios como el agua, tanto para el abastecimiento a centros poblados y sus
distintas actividades económicas; así como, para la generación hidroeléctrica, puede verse seriamente amenazada sino se administran estos recursos esenciales
con prudencia y equidad. Tomar las previsiones para evitar desastres socio-ambientales es responsabilidad de los gobiernos, a quienes compete la administración cuidadosa de un recurso vital en situación de riesgo potencial. El
monitoreo ambiental y los estudios climáticos de predicción se tornan en herramientas indispensables en estas circunstancias. En este artículo se analizala variabilidad climática en Venezuela y la vulnerabilidad a estos cambios durante el año 2003, tomando como base los mapas producidos por los modelos
matemáticos de predicción climática del Instituto Internacional de Investigación para la Predicción Climática, IRI, de la Universidad de Columbia y los mapas de los estudios climáticos regionales procesados por la National Oceanic and
Atmosferic Administration NOAA, U.S Departament of Commerce, que puedan contribuir a servir de alerta temprana para prevenir situaciones de excesos hídricos
o escasez, causantes potenciales de desastres y conflictividad social.
Palabras claves:
Variabilidad climática, alteración régimen hídrico, vulnerabilidad socio-
ambienta

ANALISIS DE PATRONES CLIMATICOS DE EVENTOS ENSO MEDIANTE CADENAS DE MARKOV Y MODELOS DE GRAFOS

by KARENIA CÓRDOVA SÁEZ

Resumen. El estudio de la variabilidad climática es uno de los elementos más relevantes de los estudios climatológicos... more Resumen. El estudio de la variabilidad climática es uno de los elementos más relevantes de los estudios climatológicos en
los últimos tiempos. La variabilidad del clima se refiere a variaciones en las condiciones climáticas medias y otras estadísticas
del clima (como las desviaciones típicas, los fenómenos extremos, etc.) que se extienden más allá de la escala de un fenómeno
meteorológico en particular. Esta puede deberse a procesos naturales internos, o al forzamiento externo natural o antropogénico.
Debido a la aceleración en los cambios macro-climáticos y ambientales, estos estudios de variabilidad han tomado mayor
énfasis. Uno de los procedimientos que permiten aproximarnos, a la evaluación de estos fenómenos, son las cadenas de
Markov y la teoría de grafos. El fenómeno ENSO (El Niño Southern Oscillation) se puede pensar como una cadena de Markov
que fluctúa entre tres estados, frío, neutro y caliente, de acuerdo a ciertas probabilidades de transición entre los estados. En
este artículo se presentan los grafos y los valores de las probabilidades de transición del índice BEST ENSO, para cada una de
las últimas cinco décadas consideradas 1950-2006. Se hace un breve análisis de las posibles causas de las discrepancias
entre los cinco grafos obtenidos. Palabras claves: variabilidad climática, ENSO, Cadenas de Markov

Heat-Related Calls To Nhs Direct: What Relevance To the Uk Heat Wave Plan?

by Giovanni Leonardi

Djamali, M., F. Biglari, K. Abdi, V. Andrieu-Ponel, J-L. de Beaulieu, M. Mashkour and Ph. Ponel (2011) Pollen analysis of coprolites from a late Pleistocene-Holocene cave deposit (Wezmeh Cave, west Iran): insights into the late Pleistocene and late Holocene vegetation and flora of the central Zagros Mountains, Journal of Archaeological Sceince, doi:10.1016/j.jas.2011.08.001

by Fereidoun Biglari

Coprolite pollen analysis is increasingly used by palynologists to reconstruct the palaeovegetation especially in the... more Coprolite pollen analysis is increasingly used by palynologists to reconstruct the palaeovegetation especially in the arid to semi-arid regions where lakes and peat bogs are scarce. This study is the first palynological analysis of coprolites in Iran to examine their potential in palaeoenvironmental reconstructions. Four pollen-rich coprolite samples were studied from the Wezmeh Cave in western Iran with a recently discovered late Quaternary (70 ka to sub-recent) faunal assemblage dominated by carnivore remains. Pollen analysis of coprolites shows that a mountain steppe dominated the glacial landscapes of the area. Only one sub-recent sample indicates the presence of dispersed tree stands. One sample was rich in Tulipa pollen suggesting that tulips were relatively abundant during the glacial periods. Cousinia (Asteraceae) pollen was found in all samples with considerable values in one sample indicating its importance in the glacial landscapes of the Zagros Mountains. This study revealed that coprolite pollen analysis can provide an invaluable source of information to understand the floristic composition of palaeolandscapes of the Irano-Turanian region.

Spatial and Temporal Connections in Groundwater Contribution to Evaporation

by Arien Lam

Citation: Lam, A., Karssenberg, D., van den Hurk, B. J. J. M., and Bierkens, M. F. P.: Spatial and temporal connections in groundwater contribution to evaporation, Hydrol. Earth Syst. Sci., 15, 2621-2630, doi:10.5194/hess-15-2621-2011, 2011.

In climate models, lateral terrestrial water fluxes are usually neglected. We estimated the contribution of vertical... more In climate models, lateral terrestrial water fluxes are usually neglected. We estimated the contribution of vertical and lateral groundwater fluxes to the land surface water budget at a subcontinental scale, by modeling convergence of groundwater and surfacewater fluxes. We present a hydrological model of the entire Danube Basin at 5 km resolution, and use it to show the importance of groundwater for the surface climate.

Results show that the contribution of groundwater to evaporation is significant, and can locally be higher than 30 % in summer. We demonstrate through the same model that this contribution also has important temporal characteristics. A wet episode can influence groundwater contribution to summer evaporation for several years afterwards. This indicates that modeling groundwater flow has the potential to augment the multi-year memory of climate models. We also show that the groundwater contribution to evaporation is local by presenting the groundwater travel times and the magnitude of groundwater convergence. Throughout the Danube Basin the lateral fluxes of groundwater are negligible when modeling at this scale and resolution. This suggests that groundwater can be adequately added in land surface models by including a lower closed groundwater reservoir of sufficient size with two-way interaction with surface water and the overlying soil layers.

Potential net effects of climate change on High Arctic Peary caribou: lessons from a spatially explicit simulation model

by Mike Ferguson

Tews, J., M.A.D. Ferguson and L. Fahrig. 2007. Potential net effects of climate change on High Arctic Peary caribou: Lessons from a spatially explicit simulation model. Ecological Modelling 207: 85-98.

It is anticipated that climate change will have a major impact on High Arctic ecosystems. Peary caribou (Rangifer... more It is anticipated that climate change will have a major impact on High Arctic ecosystems. Peary caribou (Rangifer tarandus pearyi) is a caribou subspecies endemic to the Canadian High Arctic. In the past four decades, population dynamics of Peary caribou have been subject to several population die-offs due to unfavorable winter weather with ice coating on the ground or thicker-than-usual snow cover. There is general consensus that such disturbance years may increase in frequency and severity as a result of climate change. However, there is also evidence that available forage may increase due to a longer and warmer growing season. In this study we assess the net effects of climate change with a spatially explicit simulation model calibrated with data from the Bathurst Island complex (BIC) in the Canadian High Arctic. In particular, we ask under which climate change scenarios populations depart fromthe current conditions and either suffer or benefit fromchanges in the climate. Themodel incorporatesmovement of caribou groups and annual primary productivity over 100 years. Based on the model we suggest that Peary caribou may experience significantly lower population die-offs during disturbance years if biomass increases by 50% as projected within the next 100 years and if the currently estimated proportion of inaccessible caribou forage during such disturbance events does not change with climate change. However, if forage inaccessibility in poor winters increases by more than 30% over the next 100 years, caribou may experience negative net effects of climate change. This is the first comprehensive modeling study on this species and therefore of particular importance for wildlife management and local Inuit who rely on caribou as part of their culture, identity, and diet.

Comment on 'How Plausible Are High-Frequency Sediment Supply-Driven Cycles In the Stratigraphic Record?'by S. Castelltort and J. Van Den Driessche ( …

by Jasper Knight

Sedimentary Geology, 2004, v 164 (3-4), 327-329.

The paper by Castelltort and Van Den Driessche
(2003) (hereafter termed C and VDD) provides an
interesting... more The paper by Castelltort and Van Den Driessche
(2003) (hereafter termed C and VDD) provides an
interesting perspective on the relationship between
allogenic forcing and sediment supply within river
systems. It considers these systems to comprise of
three zones (net erosion, sediment transfer, and net
deposition) with the length of the transfer zone
determining the response time of the river to allogenic
forcing (by climate, tectonics or base-level changes).
The paper by C and VDD, however, has a simple view
of the operation of river systems, is narrow in approach
and outlook, and does not consider many welldocumented
studies of fluvial sediment systems which
show complexity across many spatial and temporal
scales. This comment highlights conceptual weaknesses
in C and VDD’s paper and considers some
alternative ways at looking at the operation of river
sediment systems.

Significance of Solar Variability and Milanković Cycles in the Current Global Temperature Trends (draft)

by Emmanuel Rodulfo

We re-examine the importance of solar variability and Milanković cycles in the current global temperature trends. On... more We re-examine the importance of solar variability and Milanković cycles in the current global temperature trends. On millennial time scales, Milanković’s theory attributes climatic patterns on Earth to cycles in its obliquity (~41ka), apsidal precession (~22ka) and orbital eccentricity (~100ka). On shorter time scales, solar variability is believed to be more significant with its irradiance pulsating roughly every 10.7 years, modulated by a longer quasi-periodic cycle marked by the Oort, Wolf, Sporer, Maunder, and Dalton Minima which appear to have a mean return period of about 186 years. The most severe of these, the Maunder Minimum (1645-1715) when the Sun slumbered for over four decades, has been linked to the occurrence of the Little Ice Age (1350-1850). If this 186-year interval manifests as some grand cycle of the sun, then we could already be overdue for the next grand solar minimum which might explain why current solar activity is at its lowest level in decades. But whether or not the current Modern Maximum will be terminated by the next glacial period will depend upon the evolving superposition of Milanković parameters and solar variability, as well as other factors beyond the scope of this review. The current interglacial has already lingered more than a thousand years beyond its average duration and should soon be terminated by the next glacial period if all Milanković parameters, intrinsic solar variability, volcanic activity and possibly other factors beyond the scope of this review come into some critical superposition.

UWARUNKOWANIA KLIMATYCZNE AKTYWNOŚCI GEOMORFICZNEJ, WYSPA KRÓLA JERZEGO, SZETLANDY POŁUDNIOWE

by Zbigniew Zwolinski

Problemy Klimatologii Polarnej, 12: 33-63.

The paper presents the proposal of a method for an indirect evaluation of geomorphic activity on ice-free areas on... more The paper presents the proposal of a method for an indirect evaluation of geomorphic activity on ice-free areas on King George Island (South Shetlands, West Antarctica) through analysis of climatic conditions affecting the mobility of mineral matter. It was assumed that weather conditions affected the movement of mineral matter, which in turn determined geomorphic activity on ice-free areas, which currently occupy over 25 km2 of Admiralty Bay. On the basis of encoded values of six variables: air temperature, wind speed, rainfall, sunshine, ground temperature, and thickness of snow cover, diurnal types of the efficiency of mineral matter circulation were determined which were then clustered using the k-means method. After the cumulation of results for 7-day periods, a total of 59 homogeneous periods were obtained characterised by diurnal types of geomorphic activity (1, 2 and 3) in the observation period from April 10, 1990 to January 13, 1994. The summer season is a period with a high efficiency of mineral matter circulation and geomorphic activity, while winter time is one with a low efficiency of mineral matter circulation and geomorphic activity. Periods with an average efficiency of mineral matter circulation and geomorphic activity correspond to ascending and descending transition times. It is possible to associate the descending period with the autumn season in the temperate zone, while the ascending period, with spring-time.